600+ TOP MECHANICAL Engineering Questions & Answers

MECHANICAL ENGINEERING Interview Questions for freshers experienced :-

1. What is the difference between isotropic and anisotropic materials ?
Ans: If a material exhibits same mechanical properties regardless of loading direction, it is isotropic, e.g., homogeneous cast materials. Materials lacking this property are anisotropic.

2. What are orthotropic materials?
Ans: It is a special class of anisotropic materials which can be described by giving their properties in three perpendicular directions e.g. wood; composites.

3. What is view factor ?
Ans: View factor is dependent upon geometry of the two surfaces exchanging radiation.

4. What properties need to be considered for applications calling for following requirements :
(i) rigidity
(ii) strength for no plastic deformation under static load
(iii) strength to withstand overload without fracture.
(iv) wear resistance
(v) reliability and safety.
Ans: (i) Rigidity—Elastic modulus and yield strength
(ii) Strength (for no plastic deformation under static loading)—yield point
(iii) Strength (overload)—Toughness and impact resistance
(iv) Wear resistance—Hardness
(v) Reliability and safety—Endurance limit and yield point.

5. Explain the effects of alloying chromium and nickel in stainless steel.
Ans: Addition of nickel and chromium increases the tensile strength and increase in resistance to corrosion takes place.

6. Mention two types of dislocations.
Ans: Dislocation refers to a break in the continuity of the lattice. In edge dislocation, one plane of atoms gets squeezed out. In screw dislocation the lattice atoms move fom their regular ideal positions.

7. What are the principal constituents of brass?
Ans: Principal constituents of brass are copper and zinc.

8. What is Curie point ?
Ans: Curie point is the temperature at which ferromagnetic materials can no longer be magnetised by outside forces.

9. Specific strength of materials is very high when they are in fibre size but lower when they are in bar form Why ?
Ans: Crystal structure has ordered, repeating arrangement of atoms. Fibres are liable to maintain this and thus have high specific strength. As size increases, the condition of ordered and repeating arrangements can’t be guaranteed because of several types of defects and dislocations and thus the specific strength gets lower.

10. What is the percentage of carbon in cast iron ?
Ans: 2.5%.

11. Which element is added in steel to increase resistance to corrosion ?
Ans: Chromium.

12. Whether individual components in composite materials retain their characteristics or not?
Ans: yes.

13. An elastomer is a polymer when its percentage elongation rate is ?
Ans: Greater than 100%.

14. If percentage elongation of a material is more than 200%, it is classed as ?
Ans: Rubber.

15. Why is it that the maximum value which the residual stress can reach is the elastic limit of the material ?
Ans: A stress in excess of elastic limit, with no external force to oppose it, will relieve itself by plastic deformation until it reaches the value of the yield stress.

16. Why fatigue strength decreases as size of a part increases beyond around 10 mm?
Ans: Perfection of material conditions is possible at lower sizes and as size increases, it is not possible to attain uniform structure of the material.

17. Distinguish between creep and fatigue.
Ans: Creep is low and progressive deformation of a material with time under a constant stress at high temperature applications. Fatigue is the reduced tendency of material to offer resistance to applied stress under repeated or fluctuating loading condition.

18. While normal carburising and nitriding surface treatments increase fatigue strength, excessive treatment may decrease the fatigue strength. Why ?
.Ans: Normal carburising/nitriding treatments increase volume due to phase transformation at Surface and introduce residual compressive surface stress and thus increase the fatigue strength. By excessive treatment the high compressive stresses are introduced but these are balanced by high internal tensile stresses of equal value and the subsurface fatigue cracks may develop in the regions of high tensile stress and lead to early fatigue failure.

19. List at least two factors that promote transition from ductile to brittle fracture.
Ans: Manner of loading, and the rate of loading promote transition from ductile to brittle fracture. A machine member may have ductile failure under static loading but may fail in brittle fashion when the load is fluctuating. Similarly a material may evidence ductile failure under tensile loading at ordinary testing speed but if load is applied at a high velocity then failure may be brittle.

20. Which theories of failure are used for (a) ductile materials, and (b) brittle materials ?
Ans: For ductile materials, theories of failure used are maximum shear stress theory, and maximum energy of distortion theory; while for brittle materials, theory of maximum principal stress, and maximum strain are used.

21. What does thermal diffusivity of metals signify.
Ans: Thermal diffusivity is associated with the speed of propagation of heat into solids during changes in temperature with time.

22. For conduction of heat, the instantaneous rate of heat flow is product of three factors. What are these ?
Ans:

1. Area of the section of the heat flow path, perpendicular to the direction of heat flow.
2. temperature gradient, i.e. change of temperature w.r.t. length of path.
3. Thermal conductivity of material.

23. How convective heat transfer is effected and on what factors it depends ?
Ans: Convective heat transfer is effected between a solid and fluid by a combination of molecular conduction within the fluid in combination with energy transport resulting from the motion of fluid particles. It depends on boundary layer configuration, fluid properties and temperature difference.

24. Which is the common element between brass and bronze ?
Ans: Copper.

25. What does following alloy designation indicate FG 250 ?
Ans: Grey cast iron with tensile strength of 250 MPa.

26. How is ceramic defined ?
Ans: It is a solid formed by combination of metallic and non-metallic elements.

27. Give one example of metal classified as per structure as BCC, FCC, HCP and CCP.
Ans:

• BCC (body centred cubic) structure—Molybdenum
• FCC (face centred cubic) structure—Aluminium
• HCP (hexagonal closed packed) structure—Zinc
• CCP (cubic dosed packed) structure-Copper.

28. What is the name of solid solution of carbon in alpha iron and delta iron ?
Ans: Ferrite and austenite respectively.

29. Explain the difference between pearlite and cementile ?
Ans: Pearlite is eutectoid mixture of ferrite and cementile. Cementite is chemical compound of iron and carbon.

30. Give one example each of the following proportion of materials dimensional, physical, technological and mechanical.
Ans: Roughness, enthalpy, toughness, and hardness respectively.

31. For which parts the Wahl factor and Lewis form factor used ?
Ans: For springs and gears respectively.

32. How oxygen can be removed from steel during melting? What are fully killed steels ?
Ans: Oxygen can be removed by adding elements such as manganese, silicon or aluminium which, because of their high affinity for oxygen, react with it to form non-metallic oxides which rise into the slag. Steels which have had most of their dissolved oxygen removed are called “fully killed steels”.

33. Hydrogen cannot be removed easily from molten steel. What harm hydrogen has on property of steel ?
Ans: Execessive hydrogen results in the formation of small fissures often described as hairline cracks or flakes in the steel. Large forgings in alloy steel are particularly sensitive to this phenomenon.

34. What is allotrope ? In what forms of cubic pattern, iron exists ?
Ans: Some elements exist in more than one crystalline form. Each form is known as “allotrope”. Iron exists in two forms of cubic pattern, namely body centered cubic (bcc) and face-centered cubic (fee).

35. What is the difference between alpha iron, delta iron and gamma iron ?
Ans: The bcc form of iron exists between room temperature and 910°C, and between 1400°C and the melting point at 1539°C. The lower temperature form is known as “alpha”-iron and the higher temperature form as “delta”-iron. The face-centered cubic form existing between 910°C and 1400°C is referred to as “gamma-iron”.

36. Metals, in general are of low strength and do not possess required physio-chemical and technological properties for a definite purpose. Alloys are therefore more than metals alone. Discuss the arrangement of atoms and structures of alloys.
Ans: Alloys are produced by melting or sintering two ore more metals, or metals and a non-metal, together. Alloys possess typical properties inherent in the metallic state. The chemical elements that make up an alloy are called its components. An alloy can consist of two or more components. The phase and structures of alloys describe the constitution, transformations and properties of metals and alloys. A combination of phases in a state of equilibrium is called a system. A phase is a homogeneous portion of a system having the same composition and the same state of aggregation throughout its volume, and separated from the other portions of the system by interfaces. For instance, a homogeneous pure metal or alloy is a single-phase system. A state in which a liquid alloy (or metal) coexists with its crystals is a two-phase system. Structure refers to the shape, size or the mutual arrangement of the corresponding phases in metals or alloys. The structural components of an alloy are its individual portions, each having a single structure with its characteristic features.

37. What is the difference between isotropic material and homogeneous material ?
Ans: In homogeneous material the composition is same throughout and in isotropic material the elastic constants are same in all directions.

38. Explain the difference between the points of inflexion and contraflexure.
Ans: At points of inflexion in a loaded beam the bending moment is zero and at points of contraflexure in loaded beam the bending moment changes sign from increasing to decreasing.

39. What is the difference between proof resilience and modulus of resilience ?
Ans: Proof resilience is the maximum strain energy that can be stored in a material without permanent deformation. Modulus of resilience is the maximum strain energy stored in a material per unit volume.

40. What is the difference between column and strut ?
Ans: Both column and strut carry compressive load. Column is always vertical but strut as member of structure could carry axial compressive load in any direction.

41. Explain the difference between ferrite, austenite and graphite ?
Ans: Ferrite is the solid solution of carbon and other constituents in alpha-iron. It is soft, ductile and relatively weak.
Austenite is the solid solution of carbon and other constituents in gamma-iron. It exists in ordinary steels at elevated temperatures, but it is also found at ordinary temperatures in some stainless steels.
Graphite has a hexagonal layer lattice. ‘

42. Explain the terms solid solution, eutectic, eutectoid and peritectic.
Ans:

• Solid Solution. When a homogeneous mixture of two (or more) atomic forms exists in solid state, it is known as solid solution.
• Eutectic. A mixture of two (or more) phases which solidify simultaneously from the liquid alloy is called an eutectic. Alloys in which the components solidify simultaneously at a constant temperature the lowest for the given system, are called eutectic alloys.
• Eutectoid. Eutectoid alloys are the alloys for which two solid phases which are completely soluble become completely insoluble on cooling before a certain temperature called eutectoid temperature.
• Peritectic. A peritectic transformation involves a reaction between a solid and liquid that form a different and new solid phase. This three phase transformation occurs at a point called peritectic point.

43. What do you understand by critical points in iron, iron-carbide diagram ?
Ans: The temperatures at which the phase changes occur are called critical points (or temperatures).

45. Why PERT is preferred over CPM for evaluation of project ?
Ans: PERT is based on the approach of multiple time estimates for each activity.

46. What is the percentage of chromium in 18 : 4 : 1 IISS ?
Ans: 4%.

47. What is stellite ?
Ans: It is a non-ferrous cast alloy containing cobalt, chromium and tungsten.

48. Which rays are produced by cobalt-60 in industrial radiography ?
Ans: Gamma rays.

49. What are killed steels and what for these are used ?
Ans: Killed steels are deoxidised in the ladle with silicon and aluminium. On solidification no gas evolution occurs in these steels because they are free from oxygen.

50. What is critical temperature in metals ?
Ans: It is the temperature at which the phase change occurs in metals.

51. Car tyres are usually made of ?
Ans: Styrene-butadine rubber.

52. What is the structure of pure iron and whether it is soft or hard ?
Ans: Ferrite and it is soft.

53. Which elements increase the corrosion resistance of steel ?
Ans: Chromium and nickel.

54. What causes hardness in steel ? How heat treatment alters properties of steel ?
Ans: The shape and distribution of the carbides in the iron determines the hardness of the steel. Carbides can be dissolved in austenite is the basis of the heat treatment of steel. If steel is heated above the A critical temperature to dissolve all the carbides, and then cooled, suitable cooling through the cooling range will produce the desired size and distribution of carbides in the ferrite, imparting different properties.

55. Explain the formation of microstructures of pearlite, bainite and martensite in steel.
Ans: If austenite containing about 0.80 percent carbon is slowly cooled through the critical temperature, ferrite and cementite are rejected simultaneously, forming alternate plates or lamellae. This microstructure is called pearlite. At temperatures just belot the A1, the transformation from austenite.to pearlite may take an appreciable time to initiate and complete, but the product will be lameller pearlite. As the transformation temperature is lowered, the time to initiate transformation shortens but the product is pearlite of increasing fineness, and at temperatures approaching 550°C it cannot be resolved into its lamellar constituents. Further deerease in transformation temperature causes a lengthening of the ncubation period and a change in structure of the product to a form known as “bainite”.
If the temperature is lowered sufficiently, the diffusion controlled nucleation and growth modes of transformation are suppressed completely and the austenite transforms by a diffusionless process in which the crystal lattice effectively shears to a new crystallographic configuration known as “martensite”. This phase has a tetragonal crystal structure and contains carbon in supersaturated solid solution.

56. How with alloying of steel it is possible to a achieve properties which can not be achieved with heat treatment ?
Ans: A prerequisite to the hardening of steels is that martensite should be formed on cooling, but this can only be achieved if the rate of cooling is great enough to suppress the formation of pearlite or bainite and in plain carbon steels this can be achieved by quenching relatively small specimens

57. What are the major effects of alloying elements?
Ans: (1) To alter the transformation temperatures and times
(2) To modify the room temperature and elevated temperature strengths of given structures by (a) stiffening the crystals and (b) introducing complex precipitates which tend to harden the steel.
(3) To modify the type of oxide film formed on the surface of the steel and thereby affect its corrosion resistance.

58. What is the difference between austenite stabilisers and ferrite stabilisers ?
Ans: Austenite stabilisers have the effect of extending the temperature range overwhich austenite is formed. Such elements are carbon, manganese, nickel, copper and cobalt.
Ferrite stabilisers have the effect of extending the temperature range over which alpha and delta ferrite are formed, which consequently reduces temperature range over which austenite is formed. Such elements are silicon, chromium, molybdenum, tungsten, titanium and niobium.

59. What are the effects of carbon on the properties of steel.
Ans: In general, an increase in carbon content produces higher ultimate strength and hardness but lowers ductility and toughness of steel alloys. Carbon also increases air-hardening tendencies and weld hardness, especially in the presence of chromium. In low-alloy steel for high-temperature applications, the carbon content is usually restricted to a maximum of about 0.15% in order to assure optimum ductility for welding, expanding, and bending operations. To minimize intergranular corrosion caused by carbide precipitation, the carbon content of austenitic (18-8 type) alloys is limited in commercial specifications to a maximum of 0.08%, or even less, i.e. 0.03% in the extremely low-carbon grades used in certain corrosion-resistant applications.
In plain carbon steels in the normalised condition, the resistance to creep at temperatures below 440°C appears to increase with carbon content up to 0.4% carbon, at higher temperatures there is
but little variation of creep properties with carbon content.
An increase in carbon content lessens the thermal and electrical conductivities of steel and increases its hardness on quenching.

60. What is the role of silicon as alloying element in steels ?
Ans: Silicon contributes greatly to the production of sound steel because of its deoxidizing and degasifying properties. When added in amounts up to 2.5%, the ultimate strength of the steel is increased without loss in ductility. Silicon in excess of 2.5% causes brittleness, and amounts higher than 5% make the steel non-malleable.
Resistance to oxidation and surface stability of steel are increased by the addition of silicon. These desirable effects partially compensate for the tendency of silicon to lower the creep properties of steel. Silicon increases the electrical resistivity of steel and decreases hysteresis losses.

61. Discuss the role of manganese in alloying steels.
Ans: Manganese is an excellent deoxidizer and sulfur neutralizer, and improves the mechanical properties of steel, notably the ratio of yield strength to tensile strength at normal temperatures. As an alloying element, manganese serves as an inexpensive means of preventing “hot shortness”. It improves rolling properties, hardenability, and resistance to wear. However manganese increases the crack sensitivity of weldments, particularly with steels of higher carbon content.

62. Define buckling factor.
Ans: It is the ratio of the equivalent length of column to the minimum radius of gyration.

63. What do you understand by catenary cable ?
Ans: A cable attached to the supports and carrying its own weight.

64. What is coaxing ?
Ans: It is the process of improving fatigue properties by first under-stressing and then increasing the stress in small increments.

65. What is difference between conjugate beam and continuous beam ?
Ans: A conjugate beam is an imaginary beam of same size as original beam and carrying a distributed load in accordance with the bending moment diagram.
A continuous beam is one which is resting on more than two supports.

66. What is isotropic material ?
Ans: It is a material having same elastic constants in all directions.

67. Explain difference between modulus of resilience and modulus of rigidity ?
Ans: Modulus of resilience is the maximum strain energy stored in a material per unit volume and modulus of rigidity is the ratio of shearing stress to the shearing strain within the elastic limit.

68. What is the difference between basic hole and basic shaft ?
Ans: A basic hole is one whose lower deviation is zero and in case of basic shaft the upper deviation is zero.

69. What for pyranometer is used ?
Ans: It is used to measure the total hemispherical solar radiation.

70. Describe transfer machines in brief.
Ans: It is an automatic machine in which workpiece alongwith fixture is transferred from one station to other automatically and several operation on workpiece are performed at each station.

71. What is burnt-out point ?
Ans: It corresponds to maximum heat flux at which transition occurs from nucleate boiling to film boiling.

72. What do you understand by eutectic ?
Ans: It is mechanical mixture of two or more phases which solidify simultaneously from the liquid alloy.

72. Explain the difference between grey iron and white iron. What is mottled iron ?
Ans: The carbon in cast iron could exist at room temperature as either iron carbide, or as graphite which is the more stable form. Irons containing carbon as graphite are soft, easily machinable and are called “grey irons”. Irons with carbon present as iron carbide are extremely hard, difficult to machine and are called “white” irons. Irons with fairly equal proportions of graphite and iron carbide have intermediate hardness and are called “mottled” irons.

73. The graphite in grey irons exists in the form of flakes which act as stress-raisers under tensile loading and consequently grey irons have relatively low tensile strength and ductility. Still grey iron is extensively used in engineering. Why ?
Ans: Grey iron is extensively used in engineering because of following characteristics.
(a) Cheapness.
(b) Low melting point and high fluidity making it suitable for castings of intricate shape.
(c) Relatively good erosion and corrosion resistance.
(d) High damping capacity, with respect to vibration.
(e) Relatively good mechanical properties under compressive loading.

74. Under what condition a convergent divergent nozzle required ?
Ans: When pressure ratio is greater than critical pressure ratio.

75. What is endurance limit and what is its value for steel ?
Ans: Endurance limit is the maximum level of fluctuating stress which can be tolerated indefinitely. In most steels this stress is approximately 50% of the ultimate tensile strength and it is defined as the stress which can be endured for ten million reversals of stress.

76. How the net work to drive a compressor and its volumetric efficiency behave with increase in clearance volume ?
Ans: Work remains unaltered and volumetric efficiency decreases.

77. What do you understand by sulphur print ?
Ans: Sulphides, when attached with dilute acid, evolve hydrogen sulphide gas which stains bromide paper and therefore can be readily detected in ordinary steels and cast irons. While sulphur is not always as harmful as is sometimes supposed, a sulphur print is a ready guide to the distribution of segregated impurities in general.

78. What is the different between brass and bronze ?
Ans: Brass is an alloy of copper with zinc; and bronze is alloy of copper with tin.

79. What is the effect of addition of zinc in copper? What is the use of 70/30 brass ?
Ans: By addition of zinc in copper, both tensile strength and elongation increases. The 70/30 brass has excellent deep drawing property and is used for making radiator fins.

80. What for admirality brass used ?
Ans: Admirality brass with 29% zinc and 1% tin has good corrosion resistance and is used for condenser and feed heater tubes. Aluminium is also added to brass to improve corrosion resistance.

81. What is the maximum use of magnesium ?
Ans: Magnesium is used to alloy with aluminium and as an additive for making SG (Spheroidal Graphite) iron.

82. What for zinc finds applications ?
Ans: Galvanizing consumes the largest proportion of zinc. Zinc is resistant to corrosion but is attacked by acids and alkalies. Zinc alloy.s are suited for making die casting since the melting point is reasonably low.

83. Which factors influence the type of fracture in failure of a material ?
Ans: Seven factors influencing type of failure are :

1. Type of material (inherent structure properties),
2. Manner of loading (Static versus dynamic),
3. Range of imposed stress,
4. Strain rate (static, dynamic, impact),
5. Stress distribution (discontinuity in material/shape),
6. temperature, and
7. surface treatment.

84. What is the name given to ratio of actual cycle efficiency and ideal cycle efficiency.
Ans: Efficiency ratio.

85. List two effects of manganese in plain carbon steels. 
Ans: Manganese increases tensile strength and hardness. It decreases weldability.

86. Name the strongest and weakest type of atomic bonds.
Ans: Metallic bond is strongest and molecular bond also known as Vander Waals bond is weakest.

87. In which process internal energy remains constant ?
Ans: Isothermal process.

88. What is temper embrittlement in alloy steels and what are its effects ?
Ans: Embrittlement attack is usually intergranular in metals, i.e. cracks progress between the grains of the polycrystalline material. It imparts a tendency to fail under a static load after a given period of time in those alloy steels which are susceptible to embrittlement.

89. What are whiskers ?
Ans: Whiskers are very small crystals which are virtually free from imperfections and dislocations.

90. What is Bauschinger effect ?
Ans: According to Bauschinger, the limit of proportionality of material does not remain constant but varies according to the direction of stress under cyclic stresses.

91. What is the difference between heat capacity and specific heat of a material ?
Ans:

• The heat capacity of a material is the amount of heat transformed to raise unit mass of a material 1 degree in temperature.
• The specific heat of a material is the ratio of the amount of heat transferred to raise unit mass of a material 1 degree in temperature to that required to raise unit mass of water 1 degree of temperature at some specified temperature.
• For most engineering purposes, heat capacities may be assumed numerically equal to;specific heats.

92. Explain the rule to find specific heat of aqueous solutions.
Ans: For aqueous solutions of salts, the specific heat can be estimated by assuming the specific heat of the solution equal to that of the water alone. Thus, for a 15% by weight solution of sodium chloride in water, the specific heat would be approximately 0.85.

93. What do you understand by latent heat ? Give four examples of latent heats.
Ans: For pure substances, the heat effects accompanying changes in state at constant pressure (no temperature change being evident) are known as latent heats. Examples of latent heats are : heat of fusion, vaporisation, sublimation, and change in crystal form.

94. Define the terms free energy and free enthalpy. What is their significance and importance ?
Ans: Free energy (or Helmholtz function) is defined as/= u -Ts.
It is equal to the work during a constant-volume isothermal reversible nonflow process.
Free enthalpy (or Gibbs function) is defined as g = h – Ts
(where u = internal energy, h = enthalpy, T = temperature, s = entropy)
Gibbs function is of particular importance in processes where chemical changes occur. For reversible isothermal steady-flow processes or for reversible constant-pressure isothermal nonflow processes, change in free energy is equal to net work.

95.Which parameter remains constant in isochoric process ?
Ans: Volume.

96. What is polytropic process ? Under what conditions it approaches isobaric, isothermal, and isometric process ? In which reversible process no work is done ?
Ans: A polytropic process is one that follows the equation pun = constant (index n may have values from – oc to + oo. This process approaches isobaric when n = 0, isothermal when n = 1, and isometric when n = . No work is done in isometric process.

97. Whether superheated steam can be treated like ideal gas ?
Ans: Yes.

98. Out of constant pressure and constant volume lines on TS diagram which line has higher slope ? And whether slope is constant or variable ?
Ans: Constant volume line. Slope is variable.

99. Whether entropy is intensive property or extensive property ?
Ans: Entropy is extensive property.

100. In which process fluid expands but does no work ?
Ans: Throttling process.

101. What is the difference between scavenging and supercharging ?
Ans: Scavenging is process of flushing out burnt gases from engine cylinder by introducing fresh air in the cylinder before exhaust stroke ends. Supercharging is the process of supplying higher mass of air by compressing the atmospheric air.

102. What are the names given to constant temperature, constant pressure, constant volume, constant internal energy, constant enthalpy, and constant entropy processes.

Ans: Isothermal, isochroic, isobaric, free expression, throttling and adiabatic processes respectively.

103. In a Rankine cycle if maximum steam pressure is increased keeping steam temperature and condenser pressure same, what will happen to dryness fraction of steam after expansion ?

Ans: It will decrease.

104. Why entropy change for a reversible adiabatic process is zero ?
Ans: Because there is no heat transfer in this process.

105. What are two essential conditions of perfect gas ?
Ans: It satisfies equation of state and its specific heats are constant.

106. Enthalpy and entropy are functions of one single parameter. Which is that ?
Ans: Temperature.

107. Why rate of condensation is higher on a polished surface compared to rusty surface ?
Ans: Polished surface promotes drop wise condensation and does not wet the surface.

108. How much resistance is offered to heat flow by drop wise condensation ?
Ans: Nil

109. What is the relationship between COP of heating and cooling ?
Ans: COP of heating is one(unity) more than COP of cooling.

110. How much is the work done in isochoric process ?
Ans: Zero.

111. When maximum discharge is obtained in nozzle ?
Ans: At the critical pressure ratio.

112. Under what condition the work done in reciprocating compressor will be least ?
Ans: It is least when compression process approaches isothermal. For this purpose, attempts are made to cool the air during compression.

113. What is the difference between stalling and surging in rotary compressions ?
Ans: Stalling is a local phenomenon and it occurs when How breaks away from the blades. Surging causes complete breakdown of flow and as such it affects the whole machine.

114. Why the electric motor of a fan with backward curved blades is never got overloaded under any condition ?
Ans: The maximum power is consumed at about 70% of maximum flow in case’of fan with backward blades. For higher flow, power consumption gets lower.

115. Why the work per kg of air flow in axial flow compressor is less compared to centrifugal compressor for same pressure ratio ?
Ans: Isentropic efficiency of axial flow compressor is higher.

116. What is the name given to portion of thermal energy to be necessarily rejected to environment ?
Ans: Anergy.

117. What is pitting ? How it is caused ?
Ans: Non uniform corrosion over the entire metal surface, but occuring only in small pits is called pitting. It is caused by lack of uniformity in metal.

118. What is caustic embrittlement ?
Ans: It is the actual physical change in metal that makes it extremely brittle and filled with minute cracks. It occurs particularly in the seams of rivetted joints and around the rivet holes.

119. Which impurities form hard scale and which impurities soft scale ?
Ans: Sulphates and chlorides of lime and magnesium form hard scale, and carbonates of lime and magnesium form soft scale.

120. What is the difference between hard water and soft water ?
Ans: Hard water contains excess of scale forming impurities and soft water contains very little or no scale forming substances.

121. Which two elements in feed water can cause corrosion of tubes and plates in boiler ?
Ans: Acid and oxygen in feed water lead to corrosion.

122. What should be done to prevent a safety valve to stick to its seat ?
Ans: Safety valve should be blown off periodically so that no corrosion can take place on valve and valve seat.

123. Why large boilers are water tube type ?
Ans: Water tube boilers raise steam fast because of large heat transfer area and positive water circulation. Thus they respond faster to fluctuations in demand. Further single tube failure does not lead to catastrophy.

124. What type of boiler does not need a steam drum ?
Ans: Super-critical pressure boiler.

125. Why manholes in vessels are usually elliptical in shape ?
Ans: Elliptical shape has minimum area of opening and thus plate is weakened the least. Further it is very convenient to insert and take out the cover plate from elliptical opening.

126. Low water in boiler drum is unsafe because it may result in overheating of water tubes in furnace. Why it is unsafe to have high water condition in boiler drum ?
Ans: High drum level does not allow steam separation to be effective and some water can be carried over with steam which is not desirable for steam turbine.

127. Why boiler is purged every time before starting firing of fuel ?
Ans: Purging ensures that any unburnt fuel in furnace is removed, otherwise it may lead to explosion.

128. What is the principle of mechanical refrigeration ?
Axis. A volatile liquid will boil under the proper conditions and in so doing will absorb heat from surrounding objects.

129. Why high latent heat of vaporisation is desirable in a refrigerant ?
Ans: A high latent heat of vaporisation of refrigerant results in small amount of refrigerant and thus lesser circulation system of refrigerant for same tonnage.

130. What is the critical temperature of a refrigerant ?
Ans: Critical temperature is the maximum temperature of a refrigerantrat which it can be condensed into liquid and beyond this it remains gas irrespective of pressure applied.

131. Maximum combustion temperature in gas turbines is of the order of 1100 to 10°C whereas same is around 00°C in I.C. engine ? Why ?
Ans: High temperature in I.C. engine can be tolerated because it lasts for a fraction of second but gas turbines have to face it continuously which metals can’t withstand.

132. Why efficiency of gas turbines is lower compared to I.C. engines ?
Ans: In gas turbines, 70% of the output of gas turbine is consumed by compressor. I.C. engines have much lower auxiliary consumption. Further combustion temperature of I.C. engines is much higher compared to gas turbine.

133. What do you understand by timed cylinder lubrication ?
Ans: For effective lubrication, lub oil needs to be injected between two piston rings when piston is at bottom of stroke so that piston rides in oi during upward movement. This way lot of lub oil can be saved and used properly.

134. What is IIUCR in relation to petrol engine ?
Ans: HUCR is highest useful compression ratio at which the fuel can be used in a specific test engine, under specified operating conditions, without knocking.

135. In some engines glycerine is used in place of water for cooling of engine. Why ?
Ans: Glycerine has boiling point of 90°C which increases its heat carrying capacity. Thus weight of coolant gets reduced and smaller riadiator can be used.

136. Why consumption of lubricating oil is more in two-stroke cycle petrol engine than four-stroke cycle petrol engine ?
Ans: In two-stroke engine lub oil is mixed with petrol and thus some lub oil is blown out through the exhaust valves by scavenging and charging air. There is no such wastage in four stroke petrol engine.

137. As compression ratio increases, thermal n increases. How is thermal n affected by weak and rich mixture strength ?
Ans: Thermal n is high for weak mixture and it decreases as mixture strength becomes rich.

138. How engine design needs to be changed to burn lean mixture ?
Ans: Engine to burn lean mixture uses high compression ratio and the highly turbulent movement of the charge is produced by the geometry of the combustion chamber.

139. Horse power of I.C. engines can be expressed as RAC rating, SAE rating, or DIN rating. To which countries these standards belong ?
Ans: U.K., USA and Germany respectively.

140. What is the use of flash chamber in a vapour compression refrigeration cycle to improve the COP of refrigeration cycle ?
Ans: When liquid refrigerant as obtained from condenser is throttled, there are some vapours. These vapours if carried through the evaporator will not contribute to refrigerating effect. Using a flash chamber at some intermediate pressure, the flash vapour at this pressure can be bled off and fed back to the compression process. The throttling process is then carried out in stages. Similarly compression process is also done in two separate compressor stages.

141. Why pistons are usually dished at top ?
Ans: Pistons are usually hollowed at top to (i) provide greater spa’e for combustion, (ii) increase surface for flue gases to act upon, and (iii) better distribution of stresses.

142. What is the function of thermostat in cooling system of an engine ?
Ans: Thermostat ensures optimum cooling because excessive cooling decreases the overall efficiency. It allows cooling water to go to radiator beyond a predetermined temperature.

143. What are the causes of failure of boiler tubes ?
Ans: Boiler tubes, usually are made from carbon steel and are subject to (a) high rates of heat transfer, (b) bending stresses due to uneven heating, especially at expanded or welded joints into headers or drums, (c) external erosion from burners and flue gas, (d) possible corrosion on the boiler side, and (e) occasional manufacturing defects.
Failure may occur due to following reasons :
(a) High thermal ratings may lead to rapid failure if the internal fluid flow is reduced for any reason. The resultant overheating leads to a failure by creep, characterised by the bulging of the tube with the eventual development of a longitudinal split.
(b) Fatigue cracking due to bending stresses occur. These are associated with change of section and/or weld undercut, where tubes are expanded or welded into headers.
(c) Failure may arise due to overstressing of a reduced section of metal.
(d) Sudden failure of the boiler tube due to corrosion arises from embrittlement of the carbon steel due to interaction between atomic hydrogen from the corrosion process and the iron carbide present in the steel.
(e) Defects in tube manufacture, although far from being a regular occurrence, can be a cause of serious trouble. Lamination in boiler tubes or score marks arising from the cold drawing of tubes, give rise to premature failure and may promote corrosion at these regions.

144. What are the causes of failure of superheater tubes ?
Ans: Superheater tubes are subjected to the most severe combination of stress, temperature and corrosive environment. In addition to high-temperature strength, resistance to corrosion is also important. For example, low-alloy ferritic steel such as -1/% Cr, 1% Mo would not be used at metal temperatures above 580°C because of inadequate resistance to corrosion and oxidation over a full service life of 100,000/150,000 hr.
Failures in superheater tubes may arise from :
(a) Prior fabrication history (b) Faulty heat treatment
(c) Consequences of welding (d) Overheating of the tube metal
(e) Gas-side corrosion (f) Stress corrosion (austenitic steels).

145. Why supercritical boilers use less amount of steel compared to non-supercritical boilers ?
Ans: Supercritical boilers do not head heavy drum for separation of steam from mixture of water and steam.

146. Out of electric heater and heat pump, which is economical in operation ?
Ans: Heat pump.

147. Which furnace burns low-ash fusion coal and retains most of the coal ash in the slag?
Ans: Cyclone furnace.

148. How the thickness of thermal boundary layer and thickness of hydrodynamic boundary layer related ?
Ans: Ratio of their thickness = (Prandtl number)-1/3.

149. What is the effect of friction on flow of steam through a nozzle ?
Ans: To decrease both mass flow rate and wetness of steam.

150. Why gas turbine power plant needs efficient compressor ?
Ans: Because a large portion of turbine work is eaten away by compressor and its inefficiency will affect net power output and cost of generation.

151. Why rockets using liquid hydrogen have higher specific impulse compared to liquid hydrocarbon ?
Ans: Liquid hydrogen has higher burning velocity.

152. Why axial flow compressor is preferred for gas turbines for aeroplanes ?
Ans: Because it has low frontal area.

153. What is the effect of inter cooling in gas turbines ?
Ans: It decreases thermal efficiency but increases net output.

154. Why iso-octane is chosen as reference fuel for S.I. engines and allotted 100 value for its octane number ?
Ans: Iso-octane permits highest compression without causing knocking.

155. Why thermal efficiency of I.C. engines is more than that of gas turbine plant ?
Ans: In I.C. engine maximum temperature attained is higher than in gas turbine.

156. Which are the reference fuels for knock rating of S.I. engines ?
Ans: n-heptane and ISO-octane.

157. When effect of variations in specific heats is considered then how do maximum temperature and pressure vary compared to air standard cycle ?
Ans: Temperature increases and pressure decreases.

158. Quantities like pressure, temperature, density, viscosity, etc. are independent of mass. What are these called ?
Ans: Intensive properties.

159. The amount of radiation emitted per scm per sec is called …. ?
Ans: Emissive power.

160. In convection heat transfer, if heat flux intensity is doubled then temperature difference between solid surface and fluid will ?
Ans: Get doubled.

161. How you can define coal ?
Ans: Coal is a naturally occurring hydrocarbon that consists of the fossilised remains of buried plant debris that have undergone progressive physical and chemical alteration, called coalification, in the course of geologic time.

162. Which pollutant is major greenhouse gas and what is its effect ?
Ans: CO is major greenhouse gas and it traps the radiation of heat from the sun within earth’s atmosphere.

163. In order to increase efficiency and reduce CO emissions and other emissions, clear coal technologies are receiving major attention. What are these ?
Ans: (i) Advanced pulverised and pressurised pulverised fuel combustion.
(ii) Atmospheric fluidised bed combustion and pressurised fluidised bed combustion.
(iii) Supercritical boilers.
(iv) Integrated gasification combined cycle systems.
(v) Advanced integrated gasification, including fuel cell systems.
(vi) Magneto hydrodynamic electricity generation.

164. What are the important operational performance parameters in design of fuel firing equipment ?
Ans: Fuel flexibility, electrical load following capability, reliability, availability, and maintenance ease.

165. What is the difference between total moisture and inherent moisture in coal ?
Ans: The moisture content of the bulk as sampled is referred to as total moisture, and that of the air dried sample is called inherent moisture.

166. Proximity analysis of coal provides data for a first, general assessment of a coal’s quality and type. What elements it reports ?
Ans: Moisture, volatile matter, ash and fixed carbon.

167. Ultimate analysis of coal is elementary analysis. What it is concerned with ?
Ans: Carbon, hydrogen, nitrogen, and sulphur in coal on a weight percentage basis.

168. Explain the difference between AFBC, BFBC, PFBC and PCFB in regard to fluidised bed technologies.
Ans: AFBC (Atmospheric fluidised bed combustion) process consists of forming a bed of inert materials like finely sized ash or ash mixed with sand, limestone (for sulphur removal), and solid fuel particles in a combustor and fluidising it by forcing combustion air up through the bed mixture. The gas flows thorugh bed without disturbing particles significantly but gas velocity is high enough to support the total weight of bed (fluidisation). At slightly higher velocity excess gas passes through the bed as bubbles (fluidised bed) and gives the bed the appearance of a boiling liquid.
Bubbling fluidised bed combustion (BFBC) has a defined height of bed material and operates at or near atmospheric pressure in the furnace.
Pressurised fluidised bed combustion (PFBC) system operates the bed at elevated pressure. Exhaust gases have sufficient energy to power a gas turbine, of course, gases need to be cleaned.
In fluidised combustion, as ash is removed some unburned carbon is also removed resulting in lower efficiency. In circulating fluidised bed combustion (CFBC) system, bed is operated at higher pressure leading to high heat transfer, higher combustion efficiency, and better fuel feed. Circulating fluidised beds operate with relatively high gas velocities and fine particle sizes. The maintenance of steady state conditions in a fast fluidised bed requires the continuous recycle of particles removed by the gas stream (circulating bed). The term circulating bed is often used to include fluidised bed systems containing multiple conventional bubbling beds between which bed material is exchanged.

169. What for Schmidt plot for is used in heat transfer problems ?
Ans: Schmidt plot is a graphical method for determining the temperature at any point in a body at a specified time during the transient heating or cooling period.

170. In which reactor the coolant and moderator are the same ?
Ans: Pressurised water reactor.

171. Which reactor has no moderator ?
Ans: Fast breeder reactor.

172. What are thermal neutrons ?
Ans: Thermal neutrons are slow neutrons (having energy below 1 eV) which are in thermal equilibrium with their surroundings.

173. What is big advantage of fast breeder reactor ?
Ans: It has rapid self breeding of fissile fuel during the operation of the reactor, and thus, it offers about sixty times the output with same natural uranium resources through ordinary non-breeder nuclear reactor.

174. What is the purpose of biological shield in nuclear plants ?
Ans: Biological shield of heavy concrete prevents exposure to neutrons, beta rays and gamma rays which kill living things.

175. Which two elements have same percentage in proximate and ultimate analysis of coal?
Ans: Moisture and ash.

176. On which analysis is based the Dulong’s formula for the heating value of fuel ?
Ans: On ultimate analysis.

177. Which element causes difference in higher and lower heating values of fuel ?
Ans: Hydrogen.

178. Which heating value is indicated by a calorimeter and why ?
Ans: Gross heating value because steam is condensed and heat of vapour formed is recovered.

179. State the difference between ultimate and proximate analysis of coal ?
Ans: In ultimate analysis, chemical determination of following elements is made by weight: Fixed and combined carbon, H, O, N, S, water and ash. Heating value is due to C, H and S.
In proximate analysis following constituents are mechanically determined by weight. Moisture, volatile matter, fixed carbon and ash. Heating value is due to fixed carbon and volatile matter.

180. What is fuel ratio ?
Ans: Fuel ratio is the ratio of its % age of fixed carbon to volatile matter.

181. How the analyses and calorific values of fuels can be reported ?
Ans: It may be reported as
(a) as received or fired (wet) basis
(b) dry or moisture free basis
(c) combustible or ash and moisture free basis

182. What is the difference between nuclear fission and fission chain reaction.
Ans: The process of splitting of nucleus into two almost equal fragments accompanied by release of heat is nuclear fission. Self sustained, continuing, sequence of fission reactions in a controlled manner is fission chain reaction.

183. Explain difference between fissile and fertile materials.
Ans: The materials which can give nuclear fission e.g. U 35, Pu 39, U 33 are fissile materials. Fertile material itself is not fissionable, but it can be converted to a fissionable material by irradiation of neutrons in a nuclear reactor.

184. What do you understand by fuel cycle in nuclear plants ?
Ans: Fuel cycle a series of sequential steps involved in supplying fuel to a nuclear power reactor. The steps include : Mining, refining uranium, fabrication of fuel elements, their use in nuclear reactor, chemical processing to recover remaining fissionable material, re-enrichment of fuel from recovered material, refabrication of new fuel elements, waste storage etc.

185. What is heavy water and what is its use in nuclear plants ?
Ans: Water containing heavy isotopes of hydrogen (Deuterium) is known as heavy water. Heavy water is used as a moderator. Heavy water has low cross section for absorption of neutrons than ordinary water. Heavy water slows down the fast neutrons and thus moderates the chain reaction.

186. What is a converter reactor ?
Ans: A reactor plant which is designed to produce more fuel than it consumes. The breeding is obtained by converting fertile material to fissile material.

187. Explain nuclear reactor in brief.
Ans: A plant which initiates, sustains, controls and maintains nuclear fission chain reaction and provides shielding against radioactive radiation is nuclear reactor.

188. What is the difference between conversion and enrichment ?
Ans:

• The process of converting the non fissile U 38 to fissile U-35 is also called “Conversion”. The material like U 38 which can be converted to a fissile material by the neutron flux is called “fertile material”. The conversion is obtained within the nuclear reactor during the chain reaction.
• Enrichment is the process by which the proportion of fissile uranium isotope (U-35) is increased above 0.7% (original % in natural uranium).
• The concentration of U-35 in the uranium hexafluoride is increased from the 0.7% in natural uranium to to 4%. This is called enrichment and is accomplished in an enrichment plant.

189. Disposal of radioactive waste materials and spent fuel is a major and important technology. How the waste radioactive material is disposed off ?
Ans: Nonusable fission products are radioactive and take short/medium/long time for radioactive decay to reach safe level of radioactivity. Accordingly three methods of disposal are :
(a) Zero or low radioactivity material is dispersed or stored without elaborate shielding.
(b) Medium radioactivity material is stored for short duration of about 5 years to allow decay of radioactivity.
(c) High radioactive material. They are stored in water for several months to permit radioactive decay to an accepetable low level.

190. Which nuclear reactor uses water as a coolant, moderator and reflector ?
Ans: Pressurised water reactor.

191. Which reactor produces more fissionable material than it consumes ?
Ans: Breeder reactor.

192. Which reactor uses natural uranium as fuel ?
Ans: Gas cooled reacator.

193. Which reactor uses heavy water as moderator ?
Ans: CANDU.

194. Which reactor requires no moderator ?
Ans: Breeder reactor.

195. Which reactor uses primary coolant as fluoride salts of lithium, beryllium, thorium and uranium ?
Ans: Molten salt breeder reactor.

196. Why an increase in area is required to produce an increase of velocity in case of supersonic flow ?
Ans: Increase in area for increase in velocity for supersonic flow is required because the density decreases faster than velocity increases at supersonic speeds and to maintain continuity of mass, area must increase.

197. Under what circumstances would there be an increase in pressure in a divergent nozzle ?
Ans: For subsonic flow at inlet section of a diffuser a lower velocity and higher pressure will exist at the exit section. For supersonic isentropic flow at the inlet section a higher velocity and lower pressure will exist at the exit but if a shock wave occurs in the diffuser then a higher pressure will exist at the exit.

198. Why water can’t be used as refrigerant for small refrigerating equipment ?
Ans: The refrigerant should be such that vapour volume is low so that pumping work will be low. Water vapour volume is around 4000 times compared to R- for a given mass.

199. Which parameter remains constant in a throttling process ?
Ans: Enthalpy.

200. What is the difference between isentropic process and throttlinglprocess ?
Ans: In isentropic process, heat transfer takes place and in throttling process, enthalpy before and after the process is same.

1. Why excess air is required to burn a fuel completely ?
Answer: Excess air is required to ensure adequate mixing of fuel and air, avoid smoke, minimize slagging in coal burning, and to ensure maximum steam output.

2. What is factor of evaporation ?
Answer: It is the ratio of heat change from feed water to steam and the heat of vaporization of steam at atmospheric pressure.

3. Materials which absorb neutrons and produce fissionable material are called ?
Answer: Fertile materials, such as U28 and Th22.

4. What is the process which produces fissionable material from a fertile material ?
Answer: Breeding.

5. What is burn up in connection with fissionable material ?
Answer: Burn up corresponds to destruction of fissionable material when it undergoes nuclear fission.

6. What kind of nuclear fuel is used in Narora, Kalapakkam and Rana Pratap Sagar nuclear plants ?
Answer: Natural uranium.

7. Which type of plant will you recommend for remote location if power is required in six to twelve months time ?
Answer: Diesel engine power plant.

8. Under what condition a nuclear reaction is said to be critical ?
Answer: For critical condition, the reaction should continue at a steady rate which is possible when rate of production of neutrons is same as the combined rate of absorption of neutrons and the rate of leakage of neutrons.

9. If a nuclear reactor generates more fuel that it consumes, it is called ______ ?
Answer: Fast breeder reactor.

10. Natural uranium contains only 0.7% U25 which is capable of switching chain nuclear reaction. How this percentage is increased ?
Answer: Percentage of U25 in natural uranium is increased by a process called uranium enrichment.

11. Why the vane passages are gradually increased in size in successive wheels in steam turbine ?
Answer: The velocity of steam decreases in successive stages and to accommodate same flow per unit time, the area of flow must increase.

12. At what pressure and temperature the density of water and steam is same ?
Answer: At 225 kg/cm2 and 74.6° C.

13. What is the latent heat of evaporation at critical point ?
Answer: Zero.

14. How much space steam will occupy at atmospheric pressure corresponding to 1 kg of water ?
Answer: 100 times the space occupied by 1 kg of water.

15. What is meant by quality of steam ?
Answer: It refers to amount of unevaporated moisture in steam. If steam is perfectly dry, it’s quality is 100%.

16. What is diagram efficiency in steam turbine ?

Answer: Diagram efficiency = Change in K.E./kg / Energy suppled/kg.

17. What do you understand by effectiveness of heat exchanger ?
Answer: Effectiveness of heat exchanger = actual heat transfer/maximum possible heat transfer.

18. If superheat and condenser temperatures are unchanged and if pressure of steam is increased, then what happens to dryness fraction of steam after isentropic expansion ?
Answer: It will decrease.

19. As pressure of steam is increased, why reheating is necessary?
Answer: As pressure is increased, the dryness fraction of steam lowers on isentropic expansion. Therefore, steam has to be reheated after partial expansion so that dryness fraction remains within limits after expansion.

20. What is boundary layer thickness in free convection case ?
Answer: Velocity of fluid flow at solid surface is zero and it increases rapidly as distance from solid surface becomes greater, reaches a maximum value and then decreases to that of undisturbed fluid. The distance between the solid surface and point where boundary layer velocity equals undisturbed flow (edge) is called boundary layer thickness.

21. What do you understand by forced convection ?
Answer: When convection heat transfer occurs between a solid body and a fluid and where circulation of fluid is caused and controlled by some mechanical.

22. In radiative heat transfer, a gray surface is one whose emissivity is _____ ?
Answer: Independent of wavelength.

23. What is the effect of water injection and steam injection in gas turbine of heat rate and power output ?
Answer: Water injection results in higher mass flow rate through turbine section and as rich electrical output is increased. However it increases gas turbine heat rate because of the additional heat consumption required to vaporise the water.
Steam injection increases power output and decreases heat rate because of its higher energy entering the combustion zone.

24. Water/steam injection in gas turbines increases power output. What is the limit and reasons for same ?
Answer: Water/steam injection is not allowed beyond 5% of compressor flow to avoid flame out in combustion and to minimise operating cost and impact on inspection intervals.

25. What are the advantages and drawbacks of centrifugal compressor and axial flow compressors in gas turbines?
Answer: Centrifugal compressors have following advantages :
—short length due to high pressure ratio attained in a single stage.
—simple in design, easy to manufacture, rugged in construction, less costly.
—more reliable in operation under all operating condition.
—less susceptible to the effects of deposits left on flow path.
—less sensitive to the fouling of the flow path.
—Good efficiency over a wide range of operation.
Drawback is larger cross-section area for same capacity and its unsuitability for high pressure ratios.
Axial flow compressor is more popular due to high delivery capacity, high compression ratio due to many stages, high efficiency (85-90%), low cross sectional area. Its drawback is sophisticated design and appreciable length due to large number of stages, narrow operating range for good efficiency, higher weight and cost, high starting power.

26. What is the difference between pinch point and approach point in connection with heat recovery steam generator (IIRSG) ? How they affect performance of IIRSG ?
Answer: Pinch point is the temperature difference between the gas turbine exhaust leaving the evaporator section and the saturation temperature of steam at corresponding pressure (drum operating pressure). Approach point is the temperature difference between the temperature of steam corresponding to drum operating pressure and water temperature leaving the economiser. Both these variables affect the steam production and the cost and effectiveness of HRSG.
If pinch point is lower, total heat recovered in HRSG in higher and steam generation is also high. However lowering pinch point requires more heat exchange surface and increase in cost and draft side loss. Its optimum value is 8-10°C.
Lower is approach temperature, higher is steam production in economiser due to flashing which needs to be avoided for long life of tubes. Higher approach temperature increases the surface in evaporator section and assures higher stability.

27. How the efficiency of heat recovery in IIRSG increased ?
Answer: It can be increased by generating steam at more than one pressure.
Further improvement is possible by heating make up water/condensate in HRSG, generating low pressure saturated steam or dearation steam in HRSG using a low pressure evaporator, preheating the make up water in a heat exchanger before it enters deaerator, and circulate more water than necessary through the economiser and recirculate excess to the deaerator.

28. NO.,, reduction in gas turbines is challenge to meet environmental regulations. What measures are taken in this regard ?
Answer: NO* in gas turbines is controlled by (a) injecting water/steam into combustor, (6) using selective catalytic redaction (SCR) and non-catalytic reduction system (NRS), and (c) better combustor design.

29. What is the difference between fuel NOx and thermal NOx ?
Answer: Fuel NO* is formed by the gas phase oxidation of char nitrogen (CN~ compounds) in the fuel and thermal NO* is formed by high temperature reaction between the nitrogen and oxygen in the combustion air.

30. How steam/water injection in combustion zone lowers NOx formation.
Answer: It lowers the flame and gas temperatures.

31. What are disadvantages of injecting steam/water in combustion zone in gas turbine ?
Answer: —Increased CO at lower loads
—Increased fuel consumption
—Loss of extensively treated water
—Increased complexity of engine control
—Short life of major turbine components.

32. What for water/steam is injected in combustion zones of a gas turbine ?
Answer: Water/steam is injected to limit the amount of NOx formed by lowering the flame and gas temperatures.

33. What are improved low NOx combustors ?
Answer: Dry low NOx combustors result in improved air/fuel mixing and reduced flame temperature. The main type are lean premixed combustors, rich/quench lean combustors and catalytic combustors. Variable guide vanes are used to control the fuel-air mixture. In one design combustion chamber is designed into a series of small, lean premixed chambers.

34. What is selective catalytic reduction (SCR) method for NO* control in gas turbines ?
Answer: SCR is a post combustion method in which a catalyst is installed in flue gas where temperature could be of the order of 15-400°C. It enables vaporised NH to react with NO* in exhaust gas to form N2 and H20. Vaporised NH is injected into exhaust gases before it passes through the catalyst bed. This process can achieve in excess of 90% NOx reduction.

35. What catalyst is used in SCR process for control of NOx in gas turbines ?
Answer: V2O5 supported by titanium or a mixture of titanium and silica is generally used as catalyst. Oxides of Ti and Mo are often incorporated as moderators.

36. Measure to minimise formation of NOx inhibit complete combustion and this results in formation of CO and voltatile organic compound (VOCs). How these are controlled ?
Answer: Catalytic oxidation, a post combustion treatment at 470°-600° temperature is used to reduce emission of CO and VOCs.

37. It is usual practice to report performance characteristics of gas turbine at ISO conditions. What are these ?
Answer: ISO conditions for GT performance are : Ambient dry bulb temperature : 15°C, Relative humidity – 60%. Ambient berometric pressure 1.0 kg/cm2.

38. Which parameters influence the heat rate of gas turbines and how ?
Answer: Various parameters affecting heat rate of GT are :
(i) Lower the gas turbine inlet temperature, lower the heat rate.
(ii) Higher the compression ratio, lower the heat rate.
(iii) Higher the turbine firing temperature, lower the heat rate.
(iv) Lower the exhaust temperature, lower the heat rate.
(v) Exhaust gas flow, inlet pressure loss, exhaust pressure loss also affect heat rate.

39. Which parameters influence the performance of gas turbines ?
Answer: Ambient conditions, inlet/exhaust pressure losses, fuels, and water/steam injection flow rates’influence the performance of gas turbines.

40. Why the efficiency of superheat Rankine cycle is higher than that of simple Rankine cycle ?
Answer: Because the mean temperature of heat addition is higher for superheat cycle.

41. A Carnot cycle is to be designed to attain efficiency of 0.75. If temperature of
high temperature reservoir is 727°C, then low temperature reservoir will have to be maintained at______°C ?
Answer: – 2°C.

42. A gas having a negative Joule-Thompson coefficient, when throttled, will become …. ?
Answer: hotter.

43. What is boundary layer thickness in turbulent boundary layer ?
Answer: In ease of turbulent boundary layer, boundary layer thickness is defined as the distance from solid surface at which the fluid velocity is 99% of the undisturbed free stream velocity. Near the surface of solid, there is laminar flow which changes to buffer zone and finally turbulent region.

44. Stirling cycle with regenerative arrangement and Carnot cycle operate within same temperature limits. What can be said about thermal efficiencies of these two ?
Answer: Thermal n of both will be same.

45. How does the stagnation temperature behave along a streamline in adiabatic flow with friction ?
Answer: It remains constant.

46. What is the frequency of secondary imbalance in four-stroke engine ?
Answer: Two times the engine speed.

47. What would be the order of boundary layer in pipe flow (i) laminar (ii) transition, and (iii) fully turbulent ?
Answer: In laminar flow, boundary layer extends right from surface upto centre. In fully turbulent it may extend 5-10% of radius only whereas in transition flow, boundary layer may be from 50-60% of radius of pipe.

48. In general how the boundary layer and local film coefficient of heat transfer are related ?
Answer: In general, the thinner the boundary layer, higher the value of local heat transfer film coefficient.

49. Out of constant volume and constant pressure line, which line on T-S diagram has higher slope ?
Answer: Constant volume.

50. A heat engine and a refrigeration cycle operate between two temperature limits T1 and T2(T1 > T2). The product of efficiency of heat engine and COP of refrigeration cycle will be ?
Answer: T2/TX.

MECHANICAL ENGINEERING Interview Questions PDF ::
51. A refrigerator and a heat pump are working on the reversed Carnot cycle between the same temperature limits. How COP of refrigerator and heat pump related ?
Answer: COP of refrigerator = COP of heat pump -1.

52. For a given set of operating pressure limits of a Rankine cycle, for which cycle the efficiency will be highest ?
Answer: For regenerative cycle which approaches Carnot cycle. 1

53. A steam pipe is to be insulated by two different insulating materials of same thickness. What arrangement is preferred ?
Answer: Material with lower thermal conductivity should be used for inner layer and material with higher thermal conductivity for the outer layer.

54. Why steam is in open space and water inside tube in condensers used in power plants ?
Answer: Overall heat transfer coefficient can be increased by increasing velocity of water in tube. Further steam needs more space due to higher specific volume.

55. A condenser of a refrigeration system rejects heat at a rate of 60 kW, while its compressor consumes a power of 15 kW. What will be the coefficient of performance of this system ?
Answer: .

56. Why a refrigeration compressor designed to operate with R22 refrigerant can’t be operated with R12 ?
Answer: Condensing pressure of R22 at any given temperature is higher than that of R12.

57. Leakage of Freon-12 refrigerant can not be easly detected, still it is preferred for air-conditioning. Why ?
Answer: Leakage of Freon-12 can’t attain total concentration but it has all desirable characteristics as good refrigerant.

58. In which season the process of humidification and in which season dehumidifi-cation is used in air-conditioning ?
Answer: Humidification in summer and dehumidification in winter.

59. What is the name given to combined process of cooling and humidifying ?
Answer: Evaporative Cooling.

60. Which refrigerant is used for ice plant and transport refrigeration ?
Answer: Ammonia and CO2 respectively.

61. Which cycle is used in vapour compression and gas cycle refrigerantion system ?
Answer: Brayton cycle, and Bell-Coleman cycle.

62. In what connection Wilson line and Willan’s line used ?
Answer: Wilson line represents saturation line on the Mollier diagram. Willan’s line is connected with determination of frictional power in IC engines.

63. How the characteristics of fuel like front end volatility, mid-range volatility and tail end volatility affect S.I. engines ?
Answer: These characteristics affect SI engines in cold starting, icing of carburettor and dilution in crankcase respectively.

64. What would be the approximate air fuel ratio at time of cold start, part load operation, full load, and idling ?
Answer: 10, 12.5 and 16 respectively.

65. Name pressure compounded and velocity compounded turbine.
Answer: Rateau and Curtis respectively.

66. What is the nature of curve in case of transfer of heat by conduction through a cylindrical wall and through a spherical wall ?
Answer: Logarithmic and hyperbolic.

67. What is radiosity ?
Answer: It is the rate at which radiation leaves a surface.

68. When the compressibility effects become significant in heat transfer problems in high speed flow ?
Answer: Compressibility effects usually become significant at gas flow velocities greater than 0.5 times the velocity of sound.

69. What is the name given to process of removing non condensables in steam and other vapour cycles ?
Answer: Deaeration process.

70. We often come across use of jet pumps in process industry ? What is the reason for this ?
Answer: Jet pumps are easy to maintain and can be used to transport gases, liquids and mixtures of both.

71. When it can be said that a fluid is Newtonian ?
Answer: When the shear stress is direcly proportional to velocity gradient.

72. Why alcohol can’t be used in diesel engine ?
Answer: Alcohol has low cetane number and thus its ignition is prevented by compression.

73. Out of 2 stroke SI engine, 4 stroke SI engine, and 4 stroke CI engine, how the brake thermal efficiency behaves if these are to be used for road vehicles ?
Answer: 4 stroke CI engine has highest brake thermal efficiency followed by 4 stroke SI engine and the 2 stroke SI has lowest brake thermal efficiency.

74. A jet engine is used to drive a vehicle. When its mechanical efficiency will be maximum ?
Answer: It will be maximum when vehicle speed approaches the relative velocity of gases at nozzle exit.

75. The knocking tendency in a S.I. engine can be reduced by increasing ?
Answer: Speed

76. How you define the emissivity of a body ?
Answer: Emissivity of a body is the ratio of the emitted radiant energy flux density to the emitted radiant energy flux density of a blackbody at the same temperature.

77. What is gray body ?
Answer: When the emissivity of material does not change with temperature, it is called gray body.

78. Define fin efficiency for extended heat transfer surfaces.
Answer: Fin efficiency is defined as the ratio of the mean temperature difference from surface to fluid divided by the temperature difference from fin to fluid at the base or root of the fin.

79. What are the harmful effects of sulphur in coal used for power generation ?
Answer: Sulphur in coal gives rise to number of ecological problems ranging from acid mine drainage to ash waste problems and air pollution due to SO2 emission. Emission of S02 is the cause of acid rain and is responsible for severe environmental damage.

80. What do you understand by microbial desulphurisation ?
Answer: Sulphur from coal can be removed by physical, chemical and microbial meAnswer: Microbial means has a number of advantages over other methods. Thiobalilius ferroxidans is the most widely used micro organism studied for coal desulphurisation. This bacteria can remove 90-98% of pyritic sulphur from coal. The reaction, of course, is slow and may take several days to several weeks to complete the reaction.

81. What causes rotation of steam turbine rotor ?
Answer: Rotation of turbine rotor is caused by centrifugal force created due to change of direction of fast flowing jet of steam.

82. What do you understand by the term coagulation ?
Answer: Impurities in water are usually in finely divided state which takes long time to settle and these usually pass through the filtering media. By adding certain chemicals (coagulants), gelatinous substances are formed which cause small particles to coalesce into groups large enough to be checked during filtering.

83. What is equivalent evaporation in a boiler plant ?
Answer: It is the amount of water that would be evaporated from water at 100°C to steam at 100°C by the same amount of heat which was actually absorbed by water and steam under operating conditions.

84. What is meant by balanced draft in boiler ?
Answer: Balanced draft refers to combination of forced and induced draft fans controlled to keep the furnace under slightly vacuum condition.

85. How is dryness fraction of steam measured ?
Answer: By using throttling calorimeter.

86. What is the difference between isentropic process and throttlinglprocess ?
Answer: In isentropic process, heat transfer takes place and in throttling process, enthalpy before and after the process is same.

87. What is the difference between pyrometer, pyranometer and pyrheliometer.
Answer: Pyrometer measures temperature by radiation principle. Pyranometer is used to measure total hemispherical solar radiation. Pyrheliometer is used to measure beam intensity by collimating the radiation.

88. What is the name given to useful part of available energy which is available for conversion to useful work ?
Answer: Exergy.

89. Does the area on PV diagram for a process represent work for both reversible and non-reversible process ?
Answer: No. Same is true for only reversible process.

90. Why work is considered as high grade of energy and heat as low grade energy ?
Answer: While work can be completely converted to heat, heat can’t be converted fully to work.

91. When coluomb friction comes into existence between two surfaces ?
Answer: When there is relative motion between them.

92. Under what condition a number of forces acting at a point are in equilibrium ?
Answer: When sum of the resolved parts in any two perpendicular directions is zero.

93. What happens to two equal and opposite coplanar couples ?
Answer: They balance each other.

94. To slide a heavy block over a rough floor by a rope with minimum force by a man, at what angle the rope should be inclined with the level of floor ?
Answer: He should incline the rope with horizontal at angle of friction between floor and block.

95. A body is dropped from a certain height. If same body were to move down a smooth inclined plane from same height, which parameters will be same on reaching the ground ?
Answer: Velocity, kinetic energy and momentum.

96. A test specimen is stressed slightly beyond the yield point and then unloaded. What happens to its yield strength ?
Answer: It will increase.

97. Out of circular, square, channel, I sections, which is most economical for a component subjected to bending ?
Answer: I section.

98. What does the area under the stress-strain curve represent ?
Answer: Energy required to cause failure.

99. A tension member of certain diameter is to be replaced by a square bar of the same material. Side of square compared to diameter will be ?
Answer: Smaller.

100. A circular bar subjected to tension is designed for a particular safety factor. If both load and diameter are doubled, then factor of safety will be _____?
Answer: doubled.

MECHANICAL ENGINEERING Interview Questions ::

1. What is anisotropy ?
Ans: The phenomenon of different properties in different directions is called anisotropy.

2. What is vapour pressure and when it becomes important ?
Ans: Vapour pressure is the partial pressure created by the vapour molecules when evaporation takes place within an enclosed space. It becomes important when negative pressures are involved.

3. Explain absolute viscosity ?
Ans: It is the ratio of shear stress and the gradient of velocity with distance between a fixed plate and moving plate (Its unit is Pa . s).

4. Define surface tension ?
Ans: Surface tension of a liquid is the work that must be done to bring enough molecules from inside the liquid to the surface to form one new unit area of that surface. (Its unit is Nm/m2 or N/m).

5. What is capillarity and when liquid rises or falls ?
Ans: Capillarity : The rise or fall of a liquid in a capillary tube caused by surface tension. The magnitude of rise or fall depends on the relative magnitudes of the cohesion of the liquid and adhesion of the liquid to the walls of the containing vessels. Capillarity is of importance in tubes smaller
than 10 mm diameter.
Rise of liquid : Liquids rise (in capillary tube) when they wet and adhesion of the liquid to the walls is greater than the cohesion of the liquid.
Fall of liquid : Liquids fall (in capillary tube) when they do not wet and the cohesion of the liquid is greater than the adhesion of the liquid to the walls.

6. What is the difference between perfect and real fluids ?
Ans: Perfect fluids are treated as if all tangential forces created by friction can be ignored.
Real fluids refer to the cases in which friction must properly be taken into account.

7. Which factors affect tool size ?
Ans: Following factors influence tool size :
1. Process variable (speed, feed and depth of cut)
2. Tool material
3. Tool geometry
4. Work piece material, its hardness, microstructure and surface condition
5. Cutting conditions.

8. When the motion of fluid is fully known ?
Ans: The motion of a fluid is fully known when the velocity of each of its particles can be specified.

9. Define fluid.
Ans: A fluid is a substance that can’t remain at rest under the action of any shear force.

10. How is the size of a vertical boring machine designated ?
Ans: The specifications of vertical boring machine are :
(i) Column height
(ii) Table size
(iii) Floor area
(iv) Weight of the job
(v) Spindle of the motor.

11. What do you mean by drill sleeve and a drill socket ?
Ans: The drill sleeve is suitable for holding only one size of shank. If the taper shank of the tool is smaller than the taper in the spindle hole, a taper sleeve is used.
When the tapered tool shank is larger than the spindle taper, drill sockets are used to hold the tools. Drill sockets are much longer in size than the drill sleeves.

12. What is nonbarotropic fluid ?
Ans: Fluid such as air for which the density is not a single-valued function of the pressure (aerostatics).

13. On account of which property, the falling drops of rain acquire superical shape.
Ans: Surface tension.

14. How you can definte standard atmospheric pressure ?
Ans: By international agreement, the standard atmospheric pressure is defined as 101.325 kN/m2.

15. What do you understand by acoustic velocity ?
Ans: Accoustic velocity is the speed of a small pressure (sound) wave in a fluid.

16. Explain the difference between centipoise and centistoke ?
Ans: Centipoise is the unit of dynamic viscosity. It is equal to 1/100 of poise, and poise = 0.1 Pa . s. Value of dynamic viscosity of water at 20°C is approximately equal to 1 Centipoise.
Centistoke is the unit of kinematic viscosity and is equal to 1/100 x stoke. Stoke is defined as 1 square centimeter per second.

17. What is saybolt seconds universal ?
Ans: Saybolt Seconds Universal (SSU) is the unit of viscosity and is equal to the time required for a gravity flow of 60 cc through saybolt universal viscometer.

18. Explain difference between cohesion, adhesion and capillarity ?
Ans: Cohesion is the attraction of like molecules.
Adhesion is the attraction of unlike molecules for each other.
Capillarity is the elevation or depression of a liquid surface in contact with a solid.

19. Differentiate between gear hobbing and gear shaping with reference to various relative motions and applications.
Ans: Gear hobbing is a continuous indexing process in which both cutting tool (a hob) and work piece rotate in a constant relationship while the hob is being fed into work. Hob is also imparted a radial feed.
Gear shaping uses a pinion type of cutter which is reciprocated with required cutting speed along the face of workpiece and is gradually fed radially to plunge. Continuous generation motion is obtained by feeding cutter to full depth and rotating the cutter and workpiece slowly.

20. What is bulk modulus of elasticity ?
Ans: It represents the compressibility of a fluid. It is the ratio of the change in unit pressure to the corresponding volume change per unit of volume.

21. What is is entropic exponent ?
Ans: It is the ratio of the specific heat of a gas at constant pressure to the specific heat at constant volume.

22. The best shape of a runner in sand casting is an inverted frustum of a cone why ?
Ans: Tapered shape with bigger diameter at top and smaller at bottom ensures avoidance of entrainment or absorption of air/gases into the metal while passing through the runner.

23. Explain difference between ideal fluid and non-newtonian fluid.
Ans: Ideal fluid is one for which resistance to shearing deformation is zero.
Non-netwtonian fluids deform in such a way that shear stress is not proportional to the rate of shearing deformation.

24. Explain the difference between poise and stoke.
Ans: Poise is the unit of viscosity in CGS unit and is measured in dyne sec/cm2.1 poise = 10_1 Pa s.
Stoke is the unit of kinematic viscosity in CGS units and is measured in cm2/s.

25. How does the pressure in an isothermal atmosphere behave ?
Ans: It increases exponentially with elevation.

26. The centre of pressure for a plane surface immersed vertically in a static liquid compared to centroid of area is always … ?
Ans: Below.

27. What is buoyant force equal to ? Define centroid of the area.
Ans: Volume of liquid displaced.
Centroid of the area : The point at which the area might be concentrated and still leave unchanged the first moment of the area around any axis. It is also the centre of gravity.

28. Define vapour pressure and on what parameters it depends ?
Ans: The pressure exerted when a solid or liquid is in equilibrium with its own vapour is called vapour pressure. It is a function of the substance and its temperature.

29. Explain the difference between steady flow, one dimensional flow, two dimensional flow and three dimensional flow ?
Ans: If at every point in the continuum, the local velocity and other fluid property, remains unchanged with time, it is referred to as steady flow.
One dimensional flow is one in which a line is necessary to describe the velocity profile.
Two dimensional flow is one in which an area is necessary to describe the velocity profile.
Three dimensional flow is one in which a volume is necessary to describe the velocity profile.

30. What is aquifer and explain difference between confined and unconfined aquifers.
Ans: Groundwater occurs in permeable, water-bearing geologic formations known as aquifers.
Confined aquifer : It is a relatively high-permeable, water-bearing formation.
Unconfined aquifer : It is a water-bearing formation with a free water table, below which the soil is saturated.

31. What do you understand by flurial hydraulics ?
Ans: The channels may be classified as rigid boundary or mobile boundary channels. Mobile boundary channels include rivers and unlined alluvial canals, the boundaries of which are made of loose soil which can be easily eroded and transported by flowing water. The study of flow of water in mobile boundary channels is dealt in flurial hydraulics.

32. By which instruments the shear stress in fluids can be measured directly ?
Ans: By Stanton tube or Preston tube.

33. On what factors does the pressure at a point as a static mass of liquid depends upon?
Ans: Specific weight of liquid and the depth below the free liquid surface.

34. What is the difference between hoop or longitudinal tension and circum-ferencial tension ?
I Ans: Hoop tension is created in the walls of a cylinder subjected to internal pressure. For thin walled cylinder (t < 0.1 d), hoop stress = pressure x radius/thickness.
Longitudinal tension in thin-walled cylinders closed at the ends is equal to half the hoop tension.

35. How much force is exterted by liquid ?
Ans: Force exerted by a liquid on a plane area A is equal to the product of the unit weight pg of the liquid, the depth hcg of the centre of gravity of the area, and the area.

36. State standard point angle and helix angle of a twist drill.
Ans: Standard point angle of twist drill is 118° and helix angle varies from 16° to 30° depending as diameter of hole.

37. Explain the difference between horizontal and vertical components of hydrostatic force ?
Ans: The horizontal component of the hydrostatic force on any surface is equal to the normal force on the vertical projection of the surface and acts through the center of pressure for the vertical projection.
Vertical component of the hydrostatic force on any surface is equal to the weight of the volume of liquid abaove the area and passes through the e.g. of the volume.

38. What should be diameter of capillary tube to avoid correction for effect of capillarity in manometer ?
Ans: Greater than 6 mm.

39. How much hydrostatic pressure acts on a curved surface ?
Ans: The horizontal component of the total hydrostatic pressure force on any surface is always equal to the total pressure on the vertical projection of the surface, and can be located through the center of pressure of this projection.
The vertical components of the total hydrostatic pressure force on any surface is always equal to the weight of the entire water column above the surface extending vertically to the free surface, and cvan be located through the cemntroid of this column.

40. How much is the horizontal component of force on a curved surface ?
Ans: Force on a vertical projection of the curved surface.

41. State Archimedes principle.
Ans: Any weight, floating or immersed in a liquid, is acted upon by a buoyant force equal to the weight of the liquid displaced. This force acts through the center of buoyancy, i.e. the e.g. of the displaced liquid.

42. What do you understand by center of buoyancy ?
Ans: Center of buoyancy is the center of gravity of the displaced liquid and buoyant force acts through it.

43. How one can establish stability of submerged body and floating body ?
Ans: A submerged body floats in stable equilibrium when the center of gravity of the body lies directly below the center of buoyancy.

44. What is neutral equilibrium ?
Ans: A submerged body is in neutral equilibrium for all positions when the center of gravity of body coincides with the center of buoyancy.

45. On what factors the stability of floating objects depends ?
Ans: Stability of floating objects depends upon whether righting or overturning moment is developed when the center of gravity and center of buoyancy move out of vertical alignment due to the shifting of position of center of buoyancy.

46. State two products each produced by forward extrusion and reverse impact extrusion.
Ans: Two examples of products made by direct extrusion are : gear profile, solder wire.
Two examples of reverse impact extrusion are : Short tubes of soft alloys, tooth paste containers.

47. What are the best geometrical shapes suggested for sheet metal drawing and spinning?
Ans: Cup shape is best suited by drawing operation. Conical shape is easiest to produce by spinning operation.

48. What are the conditions for stability of buoyant bodies ?
Ans: A floating body is stable if the center of gravity is below the metacentre.
A submerged body is stable if the center of gravity is below the center of buoyancy.

49. Define pipe flow ?
Ans: It refers to full water flow in closed conduits of circular cross section under a certain pressure gradient.

50. How much is vertical component of pressure force on a submerged curved surface ?
Ans: The weight of liquid vertically above the curved surface.

MECHANICAL ENGINEERING Interview Questions PDF free download for Freshers ::
51. Multiple coated, disposable carbide tips have more-or-less replaced brazed carbide tipped tools in CNC applications. Why ?
Ans: Disposable tips are usually indexable type and have a number of cutting edges. Very convenient gripping devices for holding such inserts on tool holders are available. A wide variety of ready made inserts are available which require no grinding or adjustment.

52. State, sequentially elements of a canned CNC drilling cycle.
Ans: Canned cycles are fixed cycles for general sequences of operations. For drilling operation, sequence of operations will be movement of drill or workpiece to position of actual drilling, movement of drill downwards till it is in the proximity of workpiece, then movement of drill at desired feed rate to sufficient depth of hole, retracting the drill above the workpiece.

54. Explain the difference between one and two dimensional flow ?
Ans: True one-dimensional flow occurs when the direction and magnitude of the velocity at all points are identical. Velocities and accelerations normal to the streamline are negligible. Two dimensional flow occurs when the fluid particles, move in planes or parallel planes and the stream-line patterns are identical in each plane.

55. What is the difference between irrotational and rotational flow ?
Ans: Irrotational flow : An ideal fluid flow in which no shear stresses occur and hence no torques exist. Rotational motion of fluid particles about their own mass centers can not exist. It can be represented by a flow net.
Rotational flow occurs when the velocity of each particle varies directly as the distance from the center of rotation.

56. Explain the difference between steady and unsteady flows.
Ans: In steady flow, at any point, the velocity of successive fluid particles is the same at successive periods of time.
Flow is unsteady when conditions at any point in a fluid change with time,

57. What is the difference between uniform and non-uniform flows ?
Ans: Uniform flow occurs when the magnitude and direction of the velocity do not change from point to point in the fluid.
Non uniform flow occurs when velocity, depth, pressure, etc. change from point to point in the fluid flow.

58. Explain the difference between stream lines and stream tube.
Ans: Stream lines are imaginary curves drawn through a fluid to indicate the direction of motion in various sections of the flow of the fluid system. There can be no flow across a streamline at any point.
Stream tube represents elementary portions of a flowing fluid bounded by a group of streamlines which confine the flow.

59. What is the advantage of independent jaw chuck ?
Ans: Irregular job can be fixed.

60. Define vorticity ?
Ans: It equals twice the angular velocity.

61. What is irrational How ?
Ans: If a flow is uniform in one region (without rotation), this property is conserved as the fluid moves into a region of space where the motion is not uniform, and the flow is termed irrotational flow.

62. What is one-seventh power law ?
Ans: According to one-seventh power law of turbulent, velocity variation corresponds to a much favoured velocity profile and the mean velocity increases as the one-seventh power of the distance from the boundary wall.

63. Mention the major difference between drilling and boring ?
Ans: Drilling Boring
(a) It is the operation of initiating a hole Boring is the operation of enlarging a drilled hole
(b) It can produce only standard holes We can produce non-standard hole
(c) Drill is a multi point tool A single point tool is used

64. What is the magnitude of buoyant force and where does the line of action of buoyant force act ?
Ans: It is equal to the volume of the liquid displaced. The line of action of buoyant force acts through the centroid of the displaced volume of the fluid.

65. What is metacentre ?
Ans: Metacentre is the point at the intersection of the buoyancy with the vertical axis of the body.

66. Define Prandtl’s pitot-static tube.
Ans: It is a combination of pressure probe and pitot tube. It is widely used for pressure measurements in wind-tunnel installations.

67. Define the term fluid friction.
Ans: The deformation of real fluids is resisted by forces caused by internal friction or viscosity. Viscosity is that property of a real fluid which creates shear forces (fluid friction) between two fluid selements.

68. Why are hydrodynamic bearings used for grinding machines in preference to ball or roller bearings ?
Ans: Hydrodynamic bearings are more suitable at high speed, better tolerances, quiet operation, higher capacity to withstand shock, lesser space requirement, better life under fatigue conditions etc.

69. Distinguish between a jig and fixture.
Ans: Jig clamps and locates parts in positive manner and guides cutting tools (drills, reamers, taps etc). Fixture is bolted or fixed securely to the machine table so that work is in correct location ship to the cutter. Fixtures are used for mass milling, turning and grinding, etc.

70. State the similarities and differences between a fixture and a jig.
Ans: Both jig and fixture positively locate, hold and clamp the workpiece. Jigs guide the tool for drilling etc but fixture has no facility to guide the cutting tools. Jigs are used for drilling etc and fixture for mass milling, turning, grinding, etc.

71.Explain the difference between relative density, viscosity and kinematic viscosity ?
Ans: Relative density is that pure number which denotes the ratio of the mass of a body to the mass of an equal volume of a substance taken as a standard. This standard is usually water (at 4°C) for solids and liquids, and air free or C02 or hydrogen (at 0°C and 1 atmosphere = 1.013 x 105 Pa pressure) for gases.
Viscosity of a fluid is that property which determines the amount of its resistance to a shearing force. It is due primarily to interaction between fluid molecules.
Kinematic viscosity is the ratio of absolute viscosity and mass density. (Its unit is m2/s).

72. A right hand helical gear is being cut on a milling machine. What changes in machine settings have to be made to cut a left hand helical gear of same pitch and number of teeth ?
Ans: For cutting right hand helical gear right side of milling table is tilted up from normal position by the helix angle. For cutting left hand helical gear, right side of table needs to be tilted down at helix angle, all other settings remaining unchanged.

73. Explain what you understand by the term hydrostatic paradox ?
Ans: Hydrostatic paradox is the phenomenon that the floor load of water in vessels of different shapes carrying water at same level depends only on the area of the bottom surface and not on the shape of the vessel.

74. Define buoyancy in brief.
Ans: Buoyancy is the vertical force exerted on the body by the fluid at rest. The buoyancy of a submerged body in a fluid at rest is equal to the weight of the fluid displaced by the body and it acts upward through the center of gravity of the displaced volume (the center of buoyancy).

75. What is the necessary condition for a body to float in stable equilibrium ?
Ans: Meta center should be above the center of gravity.

76. If liquid rotates at constant angular velocity about a vertical axis as a rigid body, then how its pressure varies at various radial distances ?
Ans: As square of the radial distance.

77. How does the velocity vary along radius in a few vortex ? .
Ans: It decreases with radius.

78. What type of flow will occur when liquid discharges at constant rate through a long, straight tapering pipe ?
Ans: Steady non-uniform flow.

79. What does continuity equation represent ?
Ans: It relates mass rate of flow along a stream tube.

80. Under what condition steady flow occurs ?
Ans: When conditions do not change with time at any point.

81. Why a drill can not drill deeper than its flute length ?
Ans: If flute submerges in a drilled hole, the chips disposal passage is blocked and the drill will get jammed in the hole.

82. When do you recommend the use of straight fluted drill ?
Ans: Drills used for brass and other soft materials and thin sheets need not be provided with any helix angle, to prevent the lips digging into the workpiece.

83. Explain velocity distribution for laminar and turbulent flows.
Ans: In case of laminar flow, the velocity distribution follows a parabolic law of variation. The maximum velocity at center of pipe is twice the average velocity. For turbulent flow, more uniform velocity distribution results.

84. In which type of flow the stream lines, streak lines and path lines are identical ?
Ans: In steady flow.

85. Under what condition a drill may not cut ?
Ans: When the cutting lips are not provided with clearance angles. It will cut if 12° clearance angle is ground.

86. Some drills have straight shanks and some have tapered shank. Why ?
Ans: Small drills (less than 12 mm diameter) are provided with straight shanks which can be held in Dniren chucks. Bigger drills have tapered shank using self holding Morse tapers which prevent gravitational fall of drill.

87. What are the main factors that are responsible for the formation of built up edge ?
Ans: The main factors that are responsible for the formation of built up edge are :
1. Extreme pressure in the cutting zone
2. High friction in the tool chip interface
3. High local temperature.

88. In which type of flow the Navier-strokes equation is useful ?
Ans: Viscous flow.

89. Explain the difference between energy line and hydraulic grade line ?
Ans: The energy line is a graphical representation of the energy at each section.
Hydraulic grade line lies below the energy line by an amount equal to the velocity head at the section.

90. What is the characteristic of equipotential line ?
Ans: It has no velocity component tangent to it.

91. How specific cutting pressure behaves with feed rate and what conclusion can be drawn from this ?
Ans: As feed rate increases, the specific cutting pressure decreases. It leads to conclude that feed rates be maximised in metal cutting process.

92. What is hydraulically rough pipe ?
Ans: When Reynolds number is very small, friction factor f becomes independent of the Reynolds number and depends only on the relative roughness height. Such a pipe behaves as hydraulically rough pipe.

93. What are the qualities of ideal tool material ?
Ans: It should be hard to resist flank wear and deformation, have high toughness to resist fracture, be chemically inert to the workpiece, be chemically stable to resist oxidation and dissolution, and have good resistance to thermal shocks.

94. What are the factors to be considered while evaluating the machinability ?
Ans: 1. Tool life
2. Rate of metal removal
3. Power required
4. Surface texture and size of component
5. Temperature of tool (or) chip.

95. Which equation is satisfied by ideal or real, laminar or turbulent flow ?
Ans: Continuity equation.

96. How to judge the unsatisfactory performance of cutting tool ?
Ans: Unsatisfactory performance of cutting tool leads to loss of dimensional accuracy, increase in surface roughness and increase in power requirements.

97. What are the criteria for judging machinability ?
Ans: Cutting speed, tool life, surface finish, cutting force/energy required, teasperature rise at cutting point.

99. What is critical velocity ?
Ans: It is the velocity below which all turbulence is damped out by the viscosity of the fluid.

100. What is laminar flow ?
Ans: In laminar flow the fluid particles move along straight, parallel paths in layers or laminae. Laminar flow is governed by the law relating shear stress to rate of angular deformation i.e. the product of the viscosity of the fluid and velocity gradient.

1. How shear forces are incurred in fluid flow ?
Answer: Shear forces between fluid particles and boundary walls and between the fluid particles themselves, result from the viscosity of the real fluid.

2. In laminar flow, how discharge is related to viscosity ?
Answer: Discharge varies inversely as viscosity.

3. What is best hydraulic section ?
Answer: Best hydraulic section is one in which for a given cross-section area, the channel section has least wetted perimeter.

4. What is best hydraulic trapezoidal section ?
Answer: It is a half-hexagon in shape.

5. What is specific energy in a channel section ?
Answer: It is defined as the energy head measured with respect to the channel bottom at the section. At any section, it is equal to sum of the velocity head and the water depth at the section.

6. What is critical depth and critical flow ?
Answer: Critical depth is the depth, at which the discharge may be delivered through the section at minimum energy.
Critical flow is the flow in open channel corresponding to critical depth.

7. What causes boundary layer separation ?
Answer: An adverse pressure gradient.

8. What is the improtance of Nose radius ?
Answer: Nose radius is favourable to long tool life and good surface finish. A sharp point on the end of a tool is highly stressed, short lived and leaves a groove in the path of cut.

9. At what point below free surface in a uniform laminar flow in a channel the point velocity is equal to mean velocity of flow ?
Answer: At 0.577 depth of channel.

10. What is the value of friction factor for smooth pile when Reynolds number is approximately = 10G ?
Answer: 0.01.

11. How hydraulic grade line and free surface of open channel flow related ?
Answer: They coincide.

12.What are the first and last elements of tool signatures ?
Answer: Back rake angle and nose radius.

14. What is open channel flow ? Explain 4 types of open channel flows.
Answer: Open channel flow has a free water surface which is normally subject to the atmospheric pressure.
Steady open channel flow : In this case the discharge and water depth at any section in the reach do not change with time during the period of interest.
Unsteady open channel flow : In this case the discharge and the water depth at any section in the reach change with time.
Uniform open channel flow : In this case the discharge and the water depth remain the same in energy section in the channel reach. It is mostly steady.
Varied open channel {low : In this case the water depth and/or the discharge change along the length of the channel. It may be steady (such as flow over a spillway crest) or unstgeady (as in the case of flood waves or tidal surge).

15. When does wake occur ?
Answer: It occurs after a separation point.

16. In straight polarity, to which terminal the electrode is connected ?
Answer: Negative.

17. What is hydraulic radius ?
Answer: It is the ratio of fluid flow area/shear perimeter.

18. Define flow work.
Answer: Flow work is the amount of mechanical energy required to push or force a flowing fluid across a section boundary.

19. What do you understand by dimensional analysis ?
Answer: Dimensional analysis is the mathematics of dimensions and quantities and provides procedural techniques whereby the variables that are assumed to be significant in a problem can be formed into dimensionless parameters, the number of parameters being less than the number of variables.

20. What is hydraulic depth for open channel flow ?
Answer: It is the ratio of area and the top width of the channel section.

21. Which welding set will you select for welding both ferrous and non ferrous materials.
Answer: D.C. generator set.

22. Which welding process is a combination of arc welding and gas welding processes?
Answer: Atomic hydrogen welding.

23. What is hydraulic jump ?
Answer: It is a natural phenomenon in open channel. It is an abrupt reduction in flow velocity by means of a sudden increase of water depth in the down stream direction. Through a hydraulic jump, and high-velocity supercritical flow is changed to a low-velocity subcritical flow.

24. What is gradually varied flow ?
Answer: The changes in water depth in the open channel take place very gradually with distance. Depending on the channel slope, the surface conditions, the sectional geometry, and the discharge, these may be classified into five categories : steep channel, critical channel, mild channel, horizontal channel, and adverse channel.

25. Explain 5 types of channels.
Answer: Steep channel : In this case normal depth < critical depth. Critical channel : In this case normal depth = critical depth. Mild channel : In this case, normal depth > critical depth.
Adverse channel : In this case, the slope of channel bed < 0
Horizontal channel : In this case, the slope of channel bed = 0.

26. Mention two major differences between shaper and planer ?
Answer: Shaper Planer
(a) The cutting tool reciprocates (a) Work reciprocates
(b) The work is stationary (b) Tool is stationary
(c) Meant for small work pieces (c) Meant for large work pieces
(d) Only lighter cut can be taken (d) Heavy cuts can be taken
(e) Tools are smaller in size (e) Tools are bigger in size

27. Differentiate between drilling and reaming ?
Answer: Drilling Reaming
(a) It is the operation of initiating hole (a) Reaming is the operation of finishing and
sizing a drilled/bored hole
(b) It can be done at relatively high speeds (b) It should be done only at slow speeds
(c) Larger chips are produced (c) Less chips are produced
(d) Drill has only two flutes (d) Reamer has more than 4 flutes
(e) Drill has chisel edge (e) Reamer has a bevel edge

28. What is similarity between normal shock wave and hydraulic jump ?
Answer: Both are analogous and irreversible.

29. For what purpose chills are used in moulds ?
Answer: Chills are used to achieve directional solidification.

30. What is tumbler gear mechanism ?
Answer: Tumbler gear mechanism is a mechanism consisting of number of different sized gears keyed to the driving shaft in the form of cone and is used to give the desired direction of motion of the lathe spindle.

31. What is relative roughness of pipe ?
Answer: It is the ratio of the size of the surface imperfections to the inside diameter of the pipe.

32. What is conicity ?
Answer: The ratio of the difference in diameter of the taper to its length is termed conicity.

33. Under what condition the effect of compressibility of fluid can be neglected ?
Answer: When Mach number is less than 0.4.

34. For which type of flow the velocity distribution in a pipe is parabolic.
Answer: For uniform laminar flow.

35. What is the relationship between center line velocity and average velocity for a laminar flow in a pipe ?
Answer: Average velocity = 1/2 centre line velocity.

36. On which factor the friction factor for a smooth pipe in turbulent flow depends ?
Answer: Reynolds number.

37. What do you understand by pipe branchings ?
Answer: When water is brought by pipes to a junction where more than two pipes meet, them the total amount of water brought by pipes to a junction must always be equal to that carried away from the junction by other pipes, and all pipes that meet at the junction must share the same pressure at the junction.

38. What is pipe networks and what are the condition for network ?
Answer: Pipe network comprises a number of pipes connected together to form loops and branches. For a network,
(i) at any junction, Y.Q = 0 and
(ii) between any two junctions the total head loss is independent of the path taken.

39. What is Hardy-Cross Method ?
Answer: It is a commonly used computer program for a pipe network.

40. Explain water hammer.
Answer: The force resulting from changing the speed of the water mass (say in a pipe due to sudden change of flow rate) may cause a pressure rise in the pipe with a magnitude several times greater
than the normal static pressure in the pipe. Pressure head caused by water hammer = C (V – velocity in pipe, C = celerity).

41. What happens to impurities in centrifugal casting ?
Answer: They get collected at the center of the casting.

42. Define the terms hydraulic similitude and dimensional analysis.
Answer: Hydraulic similitude is the principle on which the model studies are based.
Dimensional analysis is the analysis of the basic relationship of the various physical quantities involved in the static and dynamic behaviors of water flow in a hydraulic structure.

43. Explain the difference between geometric similarity, kinematic similarity and dynamic similarity.
Answer: Geometric similarity : It implies similarity of form. The model is a geometric reduction of the prototype and is accomplished by maintaining a fixed ratio for all homologous lengths between the model and the prototype.
Kinematic similarity : It implies similarity in motion. Kinematic similarity between a model and the prototype is attained if the homologous moving particles have the same velocity ratio along geometrically similar paths. It involves the scale of time as well as length.
Dynamic similarity : It implies similarity in forces involved in motion.

44. Define Reynolds law ?
Answer: When the inertial force and the viscous force are considered to be the only forces governing the motion of the water, the Reynolds number of the model and the prototype must be kept at the same value.

45. When a built up edge is formed while machining ?
Answer: While machining ductile materials at high speed.

46. On what factor the friction factor for a rough pipe in turbulent flow depends ?
Answer: Relative roughness.

47. What is unit power of a turbine ?
Answer: PHP12.

48. How cavitation causes damage ?
Answer: In a a closed system (pipelines, or pumps), water vaporises rapidly in regions where the pressure drops below the vapour pressure. This phenomenon is called cavitation. The vapour bubbles formed in cavitation usually collapse in a violent manner, which may cause considerable damage to the system.

49. In milling process, how the arbor torque can be smoothend ?
Answer: Arbor torque can be smoothened by increasing number of teeth, using higher spiral angle of teeth, using higher cutting depth.

49. What are webs in a twist drill ?
Answer: Webs are the metal column in the drill which separates the flutes.

50. What is bluff body ?
Answer: It is a body with such shape that the flow is separated much ahead of its rear end resulting in a large wake, the pressure drag being much greater than the friction drag.

MECHANICAL ENGINEERING Interview Questions Answers PDF ::
51. What is bulk modulus ?
Answer: It is the ratio of hydrostatic stress to volumetric strain within the elastic limits.

52. Define boundary layer.
Answer: It is the fluid layer in the neighborhood of a solid boundary where the effects of fluid friction are predominant.

53. What is creep flow ?
Answer: It is flow at very low Reynolds number where viscous forces are larger than the inertia forces.

54. What is Torricellis theorem ?
Answer: According to it velocity of jet flowing out of a small opening is proportional to the square root of head of liquid above it.

55. How does cavitation manifest itself in a centrifugal pump ?
Answer: Usual symptoms of cavitation of pump are noise, vibration, a drop in head and capacity with a decrease in efficiency, accompanied by pitting and corrosion of the impeller vanes.

56. What happens if centrifugal pump is operated at excessive speeds ?
Answer: When a pump is operated at excessive speeds, the differential pressure developed increases and causes a powerful pulsating vacuum on the underside of the blade tips and each particle of water is pulled away from the blade, taking away with it a small particle of metal, producing pitting/grooved effect. Repeated erosive action results in complete honey combing and total destruction of blade, with resultant loss in pump performance.

57. On what parameters the head developed by a centrifugal pump depends ?
Answer: It depends upon the impeller diameter and its rotative speed.

58. Which factors determine the selection of electrolyte for electrochemical machining process ?
Answer: Electrolyte should be chemically stable and have high electrical conductivity.

59. What is the disadvantages of centrifugal pump having very low specific speed ?
Answer: For a.centrifugal pump having very low specific speed, the impeller diameter is large and narrow having excessively high disc friction and excessive hydraulic losses.

60. On what factors the efficiency of pump depends ?
Answer: Efficiency of a pump (centrifugal) depends on the size, speed, and proportions of the impeller and casing.

61. On what factors the cavitation in centrifugal pumps is dependent ?
Answer: Cavitation in centrifugal pumps depends on the velocity of water entering tne impeller and on the relatiave velocity of the impeller blades where the water is picked up.

62. What are the losses in a centrifugal pump ?
Answer: The losses in a centrifugal pump are : Friction losses due to eddies in flow, leakage, friction loss due to rotation of impeller in chamber of water, gland and bearing power losses.

63. What should be done to avoid cavitation in pumps ?
Answer: In order to avoid cavitation, the suction lift and the operating speed must be carefully chosen.

64. What will happen if speed of reciprocating pump is increased ?
Answer: If speed of a reciprocating pump is increased beyond a limit, then atmospheric pressure would be insufficient to force water into the pump at the same speed as the piston. This would a break in the continuity of the water in suction pipe (cavitation) and give rise to vibration, noise, and chemical attack by any dissolved gases which may be released from the water owing to the high vacuum and the breaking of the water column.

65. What is the order of efficiency of cenetrifugal and reciprocating pumps ?
Answer: The efficiency of centrifugal pump is of the order of 45% whereas that of reciprocting pump is around %.

66. What are the basic operations performed in a slotter ?
Answer: The different operations done in slotter are :
1. Machining grooves
2. Machining cylindrical surface
3. Machining irregular profiles.

67. How the positive displacement is obtained in rotary pumps ?
Answer: Positive displacement in rotary pumps is achieved in two ways :
(i) A rotor carries radially adjustable vanes, the outer tips of which are constrained by a circular casing, whose centre is remote from that of the rotor.
(ii) Various combinations of gears, lobes, helices, etc. within a casing arranged so that the lobes or teeth attached to each rotor pass in sequence through the same pumping space.

68. How a slotter differs from shaper ?
Answer: Slotter Shaper
(a) Ram reciprocates vertically (a) Ram reciprocates horizontally
(b) It has a circular table (b) It has a rectangular table
(c) Suited for machining internal surfaces (c) Suited for machining external surfaces
(d) Table can take less load (d) Table can take much load

69. Under what condition the flow and power of pump vary as square of the size ?
Answer: The flow and power vary as size2 when the geometric size changes as inverse of change of speed.

70. How the incidence of cavitation detected ?
Answer: The incidence of cavitation is detected by the following in order of appearance.
(i) stroboscopic observation of bubble appearance and size
(ii) sensitive acoustic tests of cavitation noise
(iii) reduction of efficiency and/or head of 3%.

71. How cavitation erosion is assessed ?
Answer: Cavitation erosion is assessed by depth of attack or weight of metal removed.

72. At which temperature the cavitation erosion is negligible and why ?
Answer: Cavitation erosion is negligible at above 300°C because the water and steam have same densities at critical temperature of 374°C and thus there is no volume change or bubble collapse in the vicinity of this range.

73. What is an arbor ?
Answer: An arbor is an accurately machined shaft for holding and driving the arbor type cutter. It is tapered at one end to fit the spindle nose and has two slots to fit the nose keys for locating and driving it.

74. For a body to float in stable equilibrium where the e.g. should be located w.r.t. metacentre ?
Answer: e.g. should be below metacentre.

75. What is the condition for a flow to be fully developed through a pipe ?
Answer: Ratio of maximum velocity to average velocity should be 2.

76. When a fluid is moving with uniform velocity, whether the pressure of fluid will depend on its depth and orientation ?
Answer: No.

77. How much is the vertical component of force on a curved surface submerged in a static liquid ?
Answer: It is equal to weight of the liquid above the curved surface.

78. On which factors depends the friction factor in a rough turbulent flow in a pipe?
Answer: It depends on pipe diameter and the condition of the pipe.

79. What does the realisation of velocity potential in fluid flow indicate ?
Answer: It indicates that flow is irrotational.

80. What is the difference between potential flow and creep flow ?
Answer: Potential flow assumes viscous forces to be zero but same is considered larger than inertia forces in creep flow.

81. For which application Mach number and Froude numbers are significant ?
Answer: Mach no. is significant in the study of projectiles and jet propulsion. Froude number is significant in the study of ship hulls.

82. What is the difference between geometric, kinematic, and dynamic similarities between model and prototype ?
Answer: Geometric similarity is mainly for same shape for model and prototype, kinematic similarity is concerned with stream line pattern, whereas dynamic similarity concerns the ratio of forces.

83. A body is floating in water. If it is displaced slightly then about which point it will oscillate.
Answer: It will oscillate about centre of buoyancy.

84. Why uniform ramming is considered desirable in green sand moulding process ?
Answer: Uniform ramming results in greater dimensional stability of a casting.

85. On what account the friction drag is experienced ?
Answer: Friction drag is experienced on separation of boundary layer.

86. What is the characteristic of centrifugally cast components ?
Answer: These have fine grain structure with high density.

87, Under what condition the separation of flow occurs ?
Answer: When pressure gradient changes abruptly.

88. What is the criterion for shaping of streamlined body ?
Answer: It is shaped to suppress the flow separation about the body and to shift the boundary layer separation to near most part of body to reduce the wake size.

89. What do you understand by entrance length and what is its value for turbulent flow in smooth pipe ?
Answer: Entrance length of flow is the initial length in which the flow develops fully such that the velocity profile remains unchanged downstream. For turbulent flow in smooth pipe, entrance length is taken as 50 x diameter of pipe.

90. Explain the difference between friction drag and pressure drag.
Answer: Friction drag is the drag force exerted by a fluid on the surface due to friction action when
the flow occurs past a flat surface at zero incidence. Pressure drag is the additional drag force on
account of the differences of pressure over the body surface when flow occurs past a surface which is
not everywhere parallel to the fluid stream. Pressure drag depends upon separation of bondary layer
and the size of wake. Friction drag is due to shear stresses generated due to viscous action.

91. What do you understand by choking in pipe line ?
Answer: When specified mass flow is not able to take place in a pipe line.

92. What is the difference between streamline body and bluff body ?
Answer: In streamline body the shape is such that separation in flow occurs past the nearmost part of the body so that wake formed is small and thus friction drag is much greater than pressure drag. In bluff body the flow gets separated much ahead of its rear resulting in large wake and thus pressure drag is much greater than the friction drag.

93. What is the difference between dressing and trueing of a grinding wheel ?
Answer: Dressing is the process used to clear the cutting surface of the grinding wheel of any dull grits and embedded swarf in order to improve the cutting action. Trueing is the process employed to bring the wheel to the required geometric shop and also to restore the cutting action of a worn wheel.

94. Whether hard grade or softer grade is required for internal grinding than external grinding?
Answer: Softer graders of wheel are required for internal grinding than for external grinding.

95. How is the velocity profile and stress distribution due to laminar flow of an incompressible flow under steady conditions in a circular pipe.
Answer: Velocity profile is parabolic with zero velocity at boundary and maximum at the centre. Shear stress distribution is linear, being maximum at boundary and zero at centre.

96. Where the maximum velocity occurs in open channels ?
Answer: Near the channel bottom.

97. Define hydraulically efficient channel cross section.
Answer: The shape of such section is that which produces minimum wetted perimeter for a given area of flow and carries maximum flow.

98. What is follower rest ?
Ans .For slender work a travelling or follower rest is used. This fits on the lathe – saddle and travels to and fro with it. By this means support is constantly provided at the position of cut. Thus the work piece being turn is rigidly held against the tool.

99. What is the meaning of the term sensitive drill press ?
Answer: A sensitive drilling press is a light, simple, bench type machine for light duty working with infinite speed ratio.

100. Why carburised machine components have high endurance limit ?
Answer: In carburised machine components, the process of carburisation introduces a compressive layer on the surface and thus endurance limit is increased.

1. What parameters influence the tool life ?
1. Tool material
2. Work material
3. Speed, feed and depth of cut
4. Tool geometry work system
5. Cutting fluid
6. Built up edge
7. Vibration behaviour of the machine tool.

2. Mention the function of intermediate stage in a generalised measurement system.
(i) Amplify signal without affecting its waveform
(ii) Remove unwanted noise signals that tend to obscure the input
(iii) Capable of doing other conditioning like differentiation/integration, A/D conversion etc.

3. What is a signal flow graph ?
A signal flow graph of a system is a graphical model in which nodes represent the system variables and directed branches between the nodes represent relationship between the variables. In a signal flow graph, a forward path originates from the input mode and terminates at output mode without encountering any mode more than once.

4. Explain the difference between rotational and irrotational flow.
In rotational flow the vorticity is non zero and in irrotational flow it is zero. In irrotational flow the net rotation of a fluid element about its own mass centre is zero as it moves from one
place to another. For it, dv/dx = du/dy.

5. Define the term stability of a feed back control system ?
A system is said to be stable if the output of a system after fluctuations, variations or oscilla-tions, settles at a reasonable value for any change in input.

6. What is meant by precision ?
Precision is defined as the ability of instrument to reproduce a certain set of readings within a given accuracy.

7. What is boundary layer ?
Boundary layer is the fluid layer in the neighbourhood of a solid boundary where the effects of fluid friction are predominant.

8. On what account the boundry layer exists ?
Boundary layer m fluid flow exists on account of fluid density.

9. Explain the difference between laminar flow and turbulent flow.
In laminar flow the fluid particles move along smooth, regular paths which can be predicted in well advance. Turbulent flow is characterised by random and erratic movements of fluid particles resulting in formation of eddies. For flow to be laminar in a pipe, the Reynold’s number is less than 2000 and for flow to be turbulent it is greater than 4000.

10. What is the difference between path line and stream line ?
A path line is a curve traced by a single fluid particle during its motion. A stream line is an imaginary line drawn in a flow field such that a tangent drawn at any point on this line represents the direction of the velocity vector. There is no flow across the stream line.

11. What is the difference between steady and unsteady flow ?
In steady flow the velocity at a given point does not change with time whereas in unsteady flow it changes with time.

12. What is stagnation point and stagnation pressure ?
A stagnation point is one at which velocity is zero. Stagnation pressure is the sum of static pressure and dynamic pressure.

13. What is the hydraulic-grade line ?
It is the line which shows tne variation of piezometric head.

14. Under what condition the thickness of thermal boundary layer and hydrody-namic boundary layer is same ? When Prandtl number is equal to unity.

15. What keeps the shaft in floating condition in hydrodynamic journal bearing ?
Hydrodynamic pressure developed in the lubricant.

16. Why the elements of higher pairs must be force closed ?
This is necessary to provide completely constrained motion.

17. What is the value of coefficient of friction for ball bearing ?
Ans: 0.1 to 0.25.

18. Why belts are subject to creep ?
Due to uneven extension and contraction of belt.

19. What is the ratio of damping coefficient to critical damping coefficient called ?
Damping factor.

20. In which type of lubrication the starting friction is low ?
In hydrostatic lubrication.

21. Whether Bernoulli’s equation is applicable for streamline straight and rotational flows ?
Ans: Yes.

22. When a plate slides over a parallel plate, what is the relationship between viscous force and the lubricant thickness ? They are directly proportional.

23. How the stability of empty ship increased.
By adding ballasts at the bottom level.

24. Define Froude number.
It is the square root of ratio of inertia force to gravity force.

25. What for Maning’s formula used ?
It is used to determine velocity of flow in pipe.

26. What is the maximum efficiency of power transmission through a pipe ?
Ans: 66.67%.

27. What is the necessary and sufficient condition for bodies in floatation to be in stable equilibrium ?
Centre of gravity of body should be located below metacentre.

28. Under what condition the thermal boundary layer thickness will be equal to the hydrodynamic boundary layer thickness ? When Prandtl number is unity.

29. How laminar boundary layer thickness varies on a flat plate ?
It is proportional to the square root of the distance from the leading edge.

30. Name the axial flow reaction turbine with adjustable vanes.
Kaplan turbine.

31. Define the degree of reaction of a turbomachine.
It is the ratio of total pressure change in the rotor to that in the stage.

32. What is meant by relative stability ?
If the system is found to be stable, then it is necessary to know the stable strength or degree of stability which is called relative stability. Phase margin and gain margins are the measures of relative stability.

33. On what factors the efficiency of a centrifugal pump depends ?
The efficiency of a centrifugal pump depends on size, speed and type number.

34. Define transducer ?
Transducer is an element which converts the signal from one physical form to another without changing the information content of the signal.

35. A 200 mm impeller of centrifugal pump develops discharge head of 2 kg/cm2. If discharge head is required as 8 kg/cm2, what should be diameter of impeller. Ans: 400 mm.

36. Why thin-plate orifice is frequently recommended for flow measurement in most of the cases ?
It is recommended because of its high accuracy, low cost, and extreme flexibility.

37. How the water flow from a hydrant in a city water system measured ?
It can be measured by allowing the flow of water from a hydrant and noting down the horizontal distance (x) where jet strikes the ground and the vertical distance (y) of outlet from ground.
Then flow = area of hydrant x

38. For the same size, length and condition of pipe, how the friction head loss changes if pipe size is varied.
Under same flow conditions the friction head loss increases as the size change to the 4.8th power.

39. How does the capacity changes in pipe flow with increase in pipe diameter if head is constant ?
At constant head, capacity is proportional to d25. .

40. How does the head change in pipe flow with change in diameter, if capacity is constant.
At constant capacity, head is proportional to

41. How head varies in pipe flow with change in flow, if pipe diameter is same.
At constant diameter, head is proportional to (flow)2.

42. Give some properties of errors ?
(i) Errors give the difference between the measured-value and the true value
(ii) Accuracy of a measurement system is measured in terms of error
(iii) A study of error helps in finding the reliability of the results.

43. Define the term contraction coefficient.
The ratio of area of jet (contracted) and the cross section of the orifice.

44. What for pycnometer is used ?
Pycnometer is used to measure specific gravity of the liquid.

45. How may types of bonded strain gauges used ?
(a) Fine wire strain gauge
(b) Metal foil strain gauge
(c) Piezo resistive gauge.

46. Name various functional elements of an instrumental system ?
(1) Primary sensing element
(2) Variable conversion (or) transducer element
(3) Variable manipulation element
(4) Data transmission element
(5) Data processing element
(6) Data presentation element
(7) Data storage and playback element.

47. Name the three stages of a generalised measuring system.
(i) Sensing and converting the input to a convenient and practicable form.
(ii) Processing/manipulating the measured variable.
(iii) Presenting the processed measured variable in quantitative form.

48. How is a Pelton turbine braked ?
A pelton wheel is braked by a nozzle directing a jet on the back of the buckets.

49. What is static pressure ? How is it measured.
The pressure caused on the walls of a pipe due to a fluid at rest inside the pipe or due to the flow of a fluid parallel to walls of the pipe is called static pressure. This static pressure is measured by inserting a pressure measuring tube into the pipe carrying the fluid so that the tube is at right angle to the fluid flow path.

50. What are the requirements of a control system ?
Stability, accuracy and speed of response are the three requirements of control system.

MECHANICAL ENGINEERING Interview Questions Answers PDF ::
51. What is the difference between weir, and submerged weir.
Any obstruction of a streamflow over which water flows is weir. When the downstream water level rises over the weir crest, it is called submerged weir.

52. What is the difference between spillway and siphon spillway ?
Spillway is an essential part of a large dam and provides an efficient and safe means of releasing flood water that exceeds the design capacity of the reservoir.
Siphon spillway is spillway designed to discharge water in a closed conduit under negative pressure.

53. What is the difference between culverts, stilling basin, and standpipe ?
Culverts are built at the points of lowest valley to pass water across the embankments of highways or railroads.
Stilling basin is transitional energy dissipating structure to avoid the damaging process by a highly accelerated spilled water.
Standpipe is used principally for alleviating the transient pressures in large pipeline system. It also works as a pressure relief valve for the upstream pipe during the turbine shut off.

54. What do you understand by run-of-river scheme in hydro power generation ?
A scheme in which the discharge is varying and only that much water can be utilised for conversion as available in the river.

55. What is the difference between firm power and secondary power in hydro power plants ?
The approximate constant and continuous power which is assured at power station and would be available throughout the year is called firm power.
In run-of-the river schemes which are generally designed for % availability of water, the firm power would be available for at least % of the years during the life of the scheme. However in some years discharge in the river may be more than % availability discharge and some extra power known as secondary power can be generated.

56. What is the criterion for determining economic diameter of power tunnel ?
The economic diameter of a power tunnel is determined such that the total value of following two factors is least
(i) annual loss of revenue on account of power head lost due to friction.
(ii) recurring annual expenditure.

57. What are the three functions served by a surge tank in a hydro plant ?
The three functions served by a surge tank are
(i) flow regulation – act as a reservoir for acceptance or delivery of water to meet requirements of load changes.
(ii) water-hammer relief or pressure regulation.
(iii) improvement in speed regulation.

58. What is the criterion to determine the economic diameter of penstock ?
The economic diameter of a penstock required to carry a discharge is the one at which annual costs due to the greater investment do not exceed the annual value of resulting increment energy output.

5. If jet ratio for a pelton wheel is 12 then number of buckets should be …. ?
0.5 x 12+ 15 = 21.

60. What is the difference between anti-friction and hydrostatic bearings ?
In anti-friction bearings rolling components are introduced between the sliding surfaces. In hydrostatic bearings lubricant is supplied at a high pressure to a pocket in the bearing.

61. What is inviscid fluid ?
It is the frictionless fluid.

62. State law of conservation of momentum ?
The ratio of change of momentum of a mass of fluid is equal to the vector sum of all external forces acting on it.

63. Define turbulent flow ?
Flow in which adjacent layers mix continuously, so that the flow pattern is unsteady, full of eddies, and apparently without any mathematically expressible regularity.

64. Define Reynold’s law of similitude ?
Two geometrically similar flow systems subject only to friction and inertia forces are dynamically similar if both have the same ‘Reynolds’ number.

65. What is the difference between boundary lubrication and fluid film lubrication ?
In boundary lubrication condition the ratio of thickness of lubrication film to surface roughness (CLA value) is less than 1 and for fluid film lubrication condition this ratio is greater than 5 and less than 100.

66. A bearing in which hydrodynamic pressure is generated due to rotation of journal is called… ?
Journal bearing.

67. For a journal running in a bearing clockwise at steady state, where will be the minimum clearance ?
To the left of the load line.

68. Out of impulse and reaction type hydraulic turbines, which has higher specific speed ?
Reaction turbine.

69. What is order of the system.
The order of the system is the order of the highest derivative of the ordinary differential equation with constant coefficients which defines the system mathematically.

70. What is Bode plot ?
Bode plot is a logarithmic plot used to represent transfer functions. The Bode plot consists of two plots namely.
(i) The plot of magnitude in db (on linear scale) vs. frequency to (on log scale)
(ii) The plot of phase angle in degrees (on linear scale) vs. frequency co (on log scale)

71. Navier stokes equation represents the conservation of which quantity ?
Momentum.

72. What are the characteristics of precision ?
(i) If a number of measurements are made on same true value, the degree of closeness of these measurements gives precision
(ii) It is a measure of the degree of repeatability or reproducibility of the measuring system.

73. What is meant by loading ?
During the act of measurement the measuring instrument takes energy from the signal source or measured medium and thus the signal source is altered. This effect is called loading.

74. Give two uses of Bode plots.
(i) They are the logarithmic plots used to represent transfer functions
(ii) They are used in the calculation of gain margin and phase margin.

75. What is the name of nondimensional group for ratio of inertia force to gravity force.
Froude number.

76. The head loss in a fully developed laminar flow in a circular pipe due to friction is directly proportional to … ?
Square of mean velocity.

77. For what type of flow, the streamlines, pathlines and streaklines are virtually identical ?
Steady flow.

78. How the streamlines and equipotential lines are related in a flow field ?
They are orthogoial everywhere in the flow field.

79. Under what kind and condition of a fluid the velocity potential exists ?
Irrotational flow.

80. Where should centre of gravity of a body lie for it to float in stable equilibrium ?
e.g. should be located below the metacentre.

81. For fully developed flow through a pipe, what is the ratio of maximum to average velocity ?
Ans: 2.

82. Out of centrifugal, axial and positive displacement pumps, which has maximum specific speed and which has minimum ?
Axial pump has maximum specific speed and reciprocating pump has minimum.

83. Specific speed of a turbine is 800. What type of turbine is this ?
Kaplan turbine.

84. In which type of lubrication system the starting friction is low ?
Hydrostatic lubrication.

85. At which point the cavitation is most likely to occur in a hydel plant ?
At turbine rotor exit.

86. What is the difference between lower pair and higher pair ?
In a kinematic pair, if the elements have surface contact when in motion, the pair is called lower pair and if elements have line or point contact the pair is called higher pair.

87. What do you understrand by inversions and how many inversions are possible in a kinematic chain having ‘n’ links ?
Inversions are different mechanisms obtained by fixing different links in a kinematic chain but keeping relative motions of links unchanged with respecat to one another. A kinematic chain with ‘n’ links can have ‘n’ inversions.

88. What is the difference between basic kinematic chain and compound kinematic chain ? What is the criteria for a chain to be constrained ?
A basic kinematic chain consists of four kinematic links and a compound kinematic chain is a constrained chain of more than four links. A chain is constrained if no. of binary joints and half of number of higher pairs is equal to 3/2 of no. of links minus 2.

89. What is the difference between a machine and a mechanism ?
A mechanism consists of links forming a constrained kinematic chain. Its function is basically to transmit or modify motion. A machine is a mechanism but here we are concerned with forces to be transmitted and it is used to modify mechanical work.

90. In which type of motion, acaceleration is directly proportional to displacement ?
SHM.

91. What is the function of a transducer element ?
The function of a transducer element is to sense and convert the desired input into a more convenient and practicable form to be handled by measurement system.

92. What is the direction of tangential acceleration ?
The direction of tangential acceleration may be same or opposite to that of angular velocity.

93. What is the number of degrees of freedom constrained in each case by the kinematic pairs.
(i) Itevolute pair, (ii) cylindrical pair, (iii) Screw pair, (iv) Spherical pair.
Ans: (i) Revolute pair—single degree of freedom.
(ii) cylindrical pair—two degrees of freedom.
(iii) Screw pair—one degree of freedom.
(iv) spherical pair—three degrees of freedom.

94. What is the purpose of D-slide valve in steam engines ?
It controls the piston position for cut off of steam, for release of steam and compression position for steam in cylinder.

95. What is the purpose of Corliss valve in place of D’-slide valve in steam engine ?
Corliss valve reduces condensation, provides independent control on admission, cut off, release and compression, and reduces driving power requirements.

96. On what factor the size of cam depends ?
Size of cam depends on base circle.

97. If base circle diameter of cam increases, what happens to pressure angle ?
It decreases.

98. If angular speed of cam is increased two times, how much jerk will be increased ?
Eight times.

99. Define primary and secondary transducers ?
A primary transducer senses a physical phenomena and converts it to an analogous output.
The analogous output is then converted into an electrical signal by secondary transducer.

100. What is the relationship between (i) axes of spin, precession, and applied gyroscopic torque and (ii) in between their planes ?
The axes of spin, precession, and applied gyroscopic torque are contained in two planes perpendicular to each other, and planes of spin, precession, and applied gyroscopic torque in the three planes perpendicular to one another.

Basic MECHANICAL ENGINEERING Interview Questions pdf ::