Category: Food Processing Unit Operations Objective Questions

250+ TOP MCQs on Heat Conduction and Answers

Food Processing Unit Operations Multiple Choice Questions on “Heat Conduction”.

1. Ice has __________ thermal conductivity than water.
a) lower
b) higher
c) same
d) very lower
Answer: b
Clarification: Ice has higher thermal conductivity than water. This is due to the molecular arrangement in solids and liquids where solid has packed structure of molecules and stronger bonding between molecules compared to liquids. Therefore the thermal conductivity of frozen foods is higher than the foods at normal temperature.

2. Which material has highest thermal conductivity?
a) Diamond
b) Copper
c) Silver
d) Bronze
Answer: a
Clarification: Diamond has highest thermal conductivity around room temperature along with the graphite and graphene. The thermal conductivity of diamond is 2000 watts per meter per Kelvin, which is five times higher than copper.

3. Which of the following is the best insulator?
a) Silica aerogels
b) Manganese aerogels
c) Potassium aerogels
d) Lead aerogels
Answer: a
Clarification: The best insulator is silica aerogels. The thermal conductivities of silica aerogel is less than 0.03 W/m*K in atmosphere.The liquid is removed from the gel without collapsing its structure, thus creating air pockets in the medium. This slows down the heat transfer and act as the insulator.

4. Are these statements about the thermal conductivity true?
Statement 1: Thermal conductivity is an extrinsic property.
Statement 2: It involves in the bulk motion of the molecules during heat transfer.
a) True, False
b) True, True
c) False, True
d) False, False
Answer: d
Clarification: Thermal conductivity is the intrinsic property of the material. It refers to its ability to conduct heat. Heat transfer by conduction involves transfer of energy within a material without any motion of the molecules during heat transfer.

5. Which of the following example does not explain conduction?
a) The heat from a hot liquid makes the cup itself hot
b) Walking on the beach on a hot summer day will warm the feet
c) A metal spoon becomes hot from the boiling water inside the pot
d) The formation of sea and land breeze
Answer: d
Clarification: The formation of sea and land breeze is an example of convection. The other examples are due to conduction where transfer of heat in internal energy by minute collision of particles and electron movement within a body.

6. Which law governs the thermal conductivity?
a) Fourier’s law
b) Pascal law
c) Newton law
d) Planks law
Answer: a
Clarification: The Fourier’s law governs the thermal conductivity. This law states that the time rate of heat transfer through a material is directly proportional to the negative gradient in the temperature and to area, at its right angle to that gradient through which the heat flows.

7. What are factors of heat capacity?
a) Heat energy, time
b) Heat energy, temperature
c) Heat energy, temperature, time
d) Temperature, time
Answer: b
Clarification: Heat energy and temperature plays an important factor in calculating heat capacity. The heat capacity is defined as the ratio of amount of heat energy supplied and change in temperature.

8. Is thermal diffusivity and thermal conductivity related?
a) True
b) False
Answer: a
Clarification: The thermal diffusivity is the thermal conductivity divided by density of the material and specific heat capacity at a constant pressure. It measures the ability to conduct thermal energy relative to its ability to the heat energy. High diffusivity means rapid heat transfer.

9. According to_________ law, the conductive heat flux is linearly proportional to the temperature gradient.
a) Fourier’s law
b) Pascal law
c) Newton law
d) Stefan-Boltzmann Law
Answer: a
Clarification: According to Fourier’s law, the conductive heat flux is linearly proportional to the temperature gradient.Pascal law deals with the fluid mechanics of the substance. Newton law deals with the heat convection. Stefan-Boltzmann Law deals with the thermal radiation.

10. Which is the slowest mode of heat transfer?
a) Conduction
b) Convection
c) Radiation
d) Both radiation and convection
Answer: a
Clarification: Conduction is the slowest mode of heat transfer because it takes place from particle to particle. The fastest mode of heat transfer is radiation as it travels at the speed of light.

250+ TOP MCQs on Size Reduction – Emulsification and Answers

Food Processing Unit Operations Assessment Questions and Answers on “Size Reduction – Emulsification”.

1. What is emulsification?
a) Process of separating two or more miscible liquids
b) Process of dispersing two or more immiscible liquids
c) Process of dispersing two or more miscible liquids
d) Process of separating two or more immiscible liquids
Answer: b
Clarification: Emulsification is the process of dispersing two or more immiscible liquids together to form a semi-stable mixture. It helps in stabilization of the product.

2. What type of emulsion is milk?
a) Oil in water
b) Water in oil
c) Water in water
d) Oil in oil
Answer: a
Clarification: In every emulsion there is a continuous phase that suspends the droplets of the other element which is known as dispersed phase. In oil-in-water emulsion, the continuous phase is the water and the dispersed phase is the oil.

3. What type of emulsion is butter?
a) Oil in water
b) Water in oil
c) Water in water
d) Oil in oil
Answer: b
Clarification: In every emulsion there is a continuous phase that suspends the droplets of the other element which is known as dispersed phase. In water-in-oil emulsion, the continuous phase is the oil and the dispersed phase is the water.

4. What is the purpose of homogenization?
a) Emulsification
b) Evaporating
c) Heating
d) Freezing
Answer: a
Clarification: The purpose of homogenization is emulsification where it breaks down fat molecules in milk and resists separation. Without homogenization process, fat molecules in milk will rise to the top and form a layer of cream.

5. What type of emulsion is mayonnaise?
a) Temporary
b) Semi-permanent
c) Permanent
d) Semi- temporary
Answer: c
Clarification: There are three types of emulsions they are temporary, semi-permanent, and permanent. An example of a temporary emulsion is simple vinaigrette while mayonnaise is a permanent emulsion.

6. What are factors that can destabilize an emulsion?
a) Temperature
b) Droplet size
c) Droplet-size distribution
d) Temperature, droplet size and droplet-size distribution
Answer: d
Clarification: Factors that can affect stabilization of an emulsion are heavy polar fractions, solids, including organic and inorganic materials, temperature, droplet size and droplet-size distribution.

7. What increases the viscosity of emulsion?
a) Stabilizers
b) Catalysts
c) Temperature
d) Pressure
Answer: a
Clarification: The viscosity is improved by stabilizers in the continuous phase of emulsions. Mobility of the droplets and their collision rate decreases. Therefore, stabilizers improve the stability of emulsions by hydrodynamic effects.

8. What is creaming in emulsions?
a) Migration of the dispersed phase of an emulsion
b) Emulsion separation into its separate ingredients
c) Migration of the continuous phase of an emulsion
d) Emulsion reaction
Answer: a
Clarification: Creaming is defined as the migration of the dispersed phase of an emulsion, under the influence of buoyancy. It occurs when isolated oil droplets combine where it sinks to the bottom in w/o emulsions or rises to the top of an o/w emulsion.

9. What is cracking in emulsions?
a) Migration of the dispersed phase of an emulsion
b) Emulsion separation into its separate ingredients
c) Migration of the continuous phase of an emulsion
d) Emulsion reaction
Answer: b
Clarification: Cracking in emulsion is defined as the separation of emulsified product into its separate ingredients where the oil and water are clearly separated and will not recombine.

10. How to determine type of emulsion?
a) Conductivity test and boiling test
b) Conductivity test and distillation
c) Dilution test and boiling test
d) Dilution test and conductivity test
Answer: d
Clarification: Emulsion Type is determined by two tests, they are dilution Test where o/w emulsion is diluted with water and w/o emulsion is diluted with oil. Conductivity test is done where electrodes are used.

Food Processing Unit Operations Assessment Questions,

250+ TOP MCQs on Mechanical Separation – Sedimentation Theory and Answers

Food Processing Unit Operations Multiple Choice Questions on “Mechanical Separation – Sedimentation Theory”.

1. Where is sedimentation used?
a) Water treatment
b) Oil production
c) Essential oil production
d) Salt production
Answer: a
Clarification: Sedimentation is the physical water treatment process using gravity to remove suspended solids and other impurities from the water.

2. What are benefits of sedimentation?
a) Effective in removing fine particles
b) Effective in removing viruses
c) Effective in removing bacteria
d) Effective in removing yeast
Answer: a
Clarification: Sedimentation is the process where by using coagulant the time required to settle out suspended solids is reduced and is very effective in removing fine particles.

3. What is sedimentation principle?
a) Centrifugal acceleration
b) Gravity
c) Electromagnetism
d) Gravity, centrifugal acceleration and electromagnetism
Answer: d
Clarification: Sedimentation is the affinity for components in suspension to settle down against a barrier. This is due to forces acting on them. These forces are gravity, centrifugal acceleration and electromagnetism.

4. Where does sedimentation value used?
a) Bread
b) Chocolate
c) Salt
d) Sugar
Answer: a
Clarification: The sedimentation value is the degree of sedimentation of flour suspended in a lactic acid solution through a standard time interval and it is a measure of the baking quality.

5. What are the factors affecting sedimentation?
a) Concentration, particle size
b) Temperature, particle size
c) Pressure, concentration
d) Pressure, particle size
Answer: a
Clarification: Factors affecting sedimentation rate are particle size, density and concentration, and fluid viscosity, convection currents in the surrounding fluid, particle shape and orientation, and chemical pretreatment of the feed suspension.

6. Are these statements about the sedimentation velocity true?
Statement 1: It is an analytical ultracentrifugation method.
Statement 2: It is used for determining the molecular mass.
a) True, False
b) True, True
c) False, True
d) False, False
Answer: b
Clarification: Sedimentation velocity is an analytical ultracentrifugation process which measures the rate of molecules movement in response to centrifugal force produced in a centrifuge. It provides information about both the shape of molecules and molecular mass.

7. Which law is related to sedimentation?
a) Gauss’s law
b) Stroke’s law
c) Dalton’s law
d) Newton’s law
Answer: b
Clarification: The sedimentation investigation is established on stokes law permitting to which the velocity at which the particles settles down depends on size, shape and weight of grain.

8. What is Zeleny test?
a) Quality of pulses
b) Quality of wheat
c) Quality of sugar
d) Quality of oil
Answer: b
Clarification: Zeleny sedimentation test is used for evaluating the quality of wheat for the baking strength of the flour. This method is applicable only to Triticum aestivum L. wheat.

9. Who invented sedimentation?
a) Newton
b) G.G. Stokes
c) Antonin Prandtl
d) Al-Kindi
Answer: b
Clarification: G.G. Stokes invented sedimentation. Newton discovered gravity. Antonin Prandtl invented centrifugation. Al-Kindi invented distillation.

10. Is soluble component be removed by using sedimentation?
a) True
b) False
Answer: b
Clarification: Sedimentation is the method of separating an insoluble substance from a liquid in which it is suspended by allowing it to settle to the bottom of the container normally by gravitational force.

250+ TOP MCQs on Contact Equilibrium Separation Process – Equipment Used for Extraction and Answers

Food Processing Unit Operations Multiple Choice Questions on “Contact Equilibrium Separation Process – Equipment Used for Extraction ”.

1. What are the classifications of extraction equipment?
a) By gravity
b) By centrifugal forces
c) By centrifugal forces and size of the particle
d) By centrifugal forces and gravity
Answer: d
Clarification: Classification of extraction equipment is based on centrifugal forces and gravity, the methods used for bringing together and separating the phases and is sub-classified according to type of contact.

2. What is basic principle behind packed towers?
a) By gravity
b) By centrifugal forces
c) By centrifugal forces and size of the particle
d) By centrifugal forces and gravity
Answer: a
Clarification: Packed columns always have nozzles for the initial distribution of each phase and droplets are present. Thus packed towers are considered as droplet extractors.

3. What are the main factors considered for the operation of extraction column?
a) Droplet size, axial dispersion
b) Droplet size distribution, axial dispersion
c) Droplet size, droplet size distribution
d) Droplet size, droplet size distribution and axial dispersion
Answer: d
Clarification: The main factors considered for the operation of extraction column are droplet size, droplet size distribution and axial dispersion. Axial dispersion follows from different phenomena like turbulence or differences in the droplet sizes, and results in lower column efficiency.

4. What are methods for regeneration of solvents?
a) Rectification
b) Evaporation
c) Crystallization
d) Rectification, evaporation, crystallization
Answer: d
Clarification: Rectification, evaporation, crystallization are the methods for regeneration of solvents. By these processes the pure products are produced and the solvent can be recycled in the extraction process.

5. Which of the following statements about centrifugal extractors are correct?
Statement 1: Discrete stages can be recognized.
Statement 2: The applied centrifugal force causes the two phases to move radially in countercurrent mode.
a) True, False
b) True, True
c) False, True
d) False, False
Answer: a
Clarification: In centrifugal extractors no discrete stages can be recognized. The principle of this design is to introduce the heavy phase close to the axis of a rotating container, while the light phase is introduced close to the periphery. The applied centrifugal force causes the two phases to move radially in a countercurrent mode in such a way that the heavy phase is moved to the periphery and the light phase to the rotation axis.

6. What is the purpose of extraction?
a) Separate an organic substance from a mixture
b) Separate an inorganic substance from a mixture
c) Separate both organic and inorganic substance from a mixture
d) Separate dust from a mixture
Answer: a
Clarification: Extraction is the recovery of a substance from a mixture by bringing it into contact with a solvent, which dissolves the desired material. It is a suitable method for separating organic substance from a mixture.

7. What are the methods of extraction used?
a) Pressing
b) Distillation
c) Solvent extraction
d) Solvent extraction, distillation method, pressing
Answer: d
Clarification: Extraction is the initial step for separating the desired natural products from the raw compounds. Some of the examples are distillation, solvent extraction, sublimation and pressing. These are divided according to the compound to be extracted and the extraction principle.

8. What is percolation extraction?
a) A method of extraction by gravity
b) A method of extraction by filtration
c) A method of extraction by sedimentation
d) A method of extraction by distillation
Answer: b
Clarification: The active compound from a product is derived through percolation method.The solvent is passed over a bed of substance which helps in the liquid extract, and this liquid extract is then recirculated through the bed for a period of time.

9. What advantages does the Soxhlet extraction have over other extraction processes?
a) Complete extraction and high efficiency
b) Complete extraction and small solvent dosage
c) Small solvent dosage and complete extraction
d) Small solvent dosage, high efficiency and complete extraction
Answer: d
Clarification: The advantage of Soxhlet extraction is that it can be extracted multiple times. Compared with the other extraction method, it has small solvent dosage, high efficiency and complete extraction.

10. What solvent is used in phytonics extraction process?
a) Hydrofluorocarbon -134a
b) ammnia
c) CFCs
d) Alcohol
Answer: a
Clarification: The Phytonics process uses a novel non-toxic solvent based on hydrofluorocarbon -134a, having a boiling point of – 25°C and a vapor pressure of 5.6 bar at ambient temperature. It is mainly used in the extraction of plant materials.

250+ TOP MCQs on Drying Rate and Answers

Food Processing Unit Operations Multiple Choice Questions on “Drying Rate”.

1. Rate of drying depends on which of the following statement?
Statement 1: Vapor pressure of water at drying temperature.
Statement 2: Vapor pressure in the external environment.
a) True, False
b) True, True
c) False, True
d) False, False
Answer: b
Clarification: Rate of drying depends on 1) equilibrium vapor pressure of water in the food 2) moisture of the food 3) vapor pressure of water at drying temperature and 4) vapor pressure in the external environment.

2. Which of the following statements are true about drying?
Statement 1: Latent heat of vaporization is not necessary.
Statement 2: Moisture must be transported out from the food.
a) True, False
b) True, True
c) False, True
d) False, False
Answer: c
Clarification: Latent heat of vaporization is necessary as it converts its liquid into vapor and the moisture must be transported out from the food to obtain dehydrated product.

3. What happens to the drying rate when it reaches critical moisture content?
a) Declines
b) Increases gradually
c) Stops
d) Becomes constant
Answer: a
Clarification: The critical moisture content is defined as the average material moisture content at which the drying rate begins to decrease. The point that shifts to the Declining drying period from Constant drying period is known as critical moisture content

4. What is the independent factor of the constant rate period?
a) Moisture content
b) Temperature
c) Pressure
d) Humidity
Answer: a
Clarification: The constant rate period is independent of moisture content in the rate of drying curve. In this period, diffusion of moisture takes place where the droplet maintains saturated surface conditions and the evaporation takes place at constant rate.

5. At what stage the case hardening of a material takes place?
a) Constant rate period
b) Falling rate period
c) Initial rate period
d) Equilibrium
Answer: a
Clarification: The case hardening is defined as the formation of a hard skin on the surface of foods which slows down the drying rate and may leads to the mold growth. It is due to quick drying during the constant rate period and this can be stopped by using cooler drying air.

6. Name the phenomenon which transfers moisture during second falling drying rate period?
a) Liquid diffusion
b) Capillary movement
c) Vapor diffusion
d) Liquid diffusion, capillary movement, and vapor diffusion.
Answer: d
Clarification: During second falling drying rate period, the moisture transfer is due to the liquid diffusion, capillary movement, and vapor diffusion because the drying rate becomes independent of conditions outside the solid.

7. What type of drying takes place when the food has high fat contents?
a) Slow
b) Fast
c) Constant
d) Quick
Answer: a
Clarification: Higher fat contents results in the slower drying rate as water is trapped within the food. The size of the food affects the drying rate in both the constant and falling rate periods.

8. How does humidity affect drying rate?
a) No effect
b) Directly proportional
c) Indirect proportional
d) Linear increase
Answer: b
Clarification: The rate of evaporation depends mainly on the relative humidity than on the temperature. But both the relative humidity and temperature are correlated. When the air temperature increases, it absorbs more liquid and the relative humidity decreases. Low relative humidity helps in faster drying.

9. What is drying constant?
a) Mechanisms of heat and mass transport phenomena
b) Mechanism of heat phenomena
c) Mechanism of mass transport phenomena
d) Mechanism of drying phenomena
Answer: a
Clarification: Drying constant describes the mechanisms of heat and mass transport phenomena and investigates the influence that certain process variables exert on moisture removal processes. Drying constant is measured through experimental studies of material moisture content removal versus time at various drying conditions.

10. What happens to the drying rate during constant rate of drying period?
a) It reduces
b) It increases
c) Constant
d) Becomes negligible
Answer: b
Clarification: During the constant rate period, free moisture persists on the surfaces and the rate of evaporation modifies very little as moisture content decreases. During this period, drying rates are high and have high inlet air temperatures than in subsequent drying stages that can be used without detrimental effect to the product. There is a gradual and relatively small increase in the temperature of the product during this period.

250+ TOP MCQs on Power for Agitation and Answers

Food Processing Unit Operations Question Paper on “Power for Agitation”.

1. Which unit operation involves the mechanically induced establishment of a flow pattern in a liquid mixture?
a) Sedimentation
b) Agitation
c) Mixing
d) Crystallization
Answer: b
Clarification: Agitation is the process involving induced circular motion of homogeneous particles to prepare a liquid mixture, mechanically. Sedimentation refers to the settling down of suspension particles whereas Mixing refers to the random distribution of initially separate ingredients. Crystallization on the other hand is the formation of clumps of solid particles due to mass transfer.

2. The figure given below is a 3 bladed device, used to produce Agitation in liquids. Name it.

a) Turbine
b) Distributor
c) Blender
d) Propeller
Answer: d
Clarification: The most common device used for agitation of liquids is the Propeller, which is a type of Impeller. Turbines are also a type of impellers, though with different fan orientations.

3. The role of Baffles is to improve mixing and remove stratification during agitation.
a) True
b) False
Answer: a
Clarification: During the process of agitation the baffles, which are one of the mechanical agitation devices used, remove stratification in the radial direction and improve mixing performance. A typical agitator vessel setup consists of 4 baffles and 1 impeller.

4. The formula Np=(frac{P}{n^3Da^5rho}) denotes which number in impeller problems?
a) Weber number
b) Froude number
c) Power number
d) Euler Number
Answer: c
Clarification: Powernumber is the ratio of inertial force to viscous force. It is dimensionless and Buckingham’s Pi theorem is applied to it, thus giving the formula Np=(frac{P}{n^3Da^5rho}) , where P is the Pressure of the liquid, n is the rotation per minute of the impeller, D is the diameter and ρ is the density of the liquid.

5. A flat blade turbine having six blades is centrally installed in a vertical tank. The tank is 6 ft (1.83 m) in diameter; the turbine is 2 ft. (0.61 m) in diameter and is positioned 2 ft (0.61 m) from the bottom of the tank. The turbine blades are 5 in. (127 mm) wide. The tank is filled to a depth of 6 ft (1.83 m) with a solution of 50 percent caustic soda, at 150°F (65.6°C), which has a viscosity of 12 cP and a density of 93.5 lb/ft3 (1498 kg/m3). The turbine is operated at 90 r/min. the tank is baffled. What power will be required to operate the mixer? (Given KL=403680).
a) 2.47 kW
b) 6.05 kW
c) 3.21 kW
d) 4.00 kW
Answer: a
Clarification: First calculate Reynold’s number. We have Da = 2 ft, n =(frac{90}{60}) = 1.5 r/s, μ= 12 X 6.27 X 10-4 = 8.06 X 10-3 lb/ft-s, ρ=93.5 lb/ft3 and g = 32.17 ft/s2.
NRe = (frac{Da^2nrho}{μ}) = (frac{2^2X1.5X93.5}{8.06 X 10^{-3}}) = 69,600
We know that at low Reynold’s number for both baffled and unbaffled tanks, the relationship is given by
Np =(frac{K_L}{N_{Re}}) = (frac{403680}{69600}) = 5.8
P = (frac{5.8 X 93.5 X 1.5^3 X 2^2}{32.17})=1821 ft-lb/s
The power requirement is 1821/550 = 2.47 kW (3.31 hp).

6. Which one is not the purpose of establishment of agitation in fluids?
a) Suspension of solid particles
b) Blending of solids
c) Blending miscible liquids
d) Promoting heat transfer
Answer: b
Clarification: Agitation is done to suspend solid particles that might have settled down or are not distributed throughout the fluid, for the dispersion of a gas through the liquid, for promoting heat transfer and for the blending of miscible liquids.

7. An agitator is selected depending upon the __________
a) Volume of liquid
b) Height of the tank
c) Power required
d) Fluid viscosity
Answer: d
Clarification: An agitator is selected depending upon the viscosity of the fluid, since that is the only way to determine the selection from the impellers of different types. This selection is independent of fluid volume, height of the tank used, and the power required in the process.

8. Name the type of impeller used for agitation of low viscosity fluids, on high speeds?
a) Propeller
b) Concave Blade Impeller
c) Straight blade turbine
d) Paddles
Answer: a
Clarification: Propellers are a type of impellers used for agitation of low viscosity fluids, on high speeds. They are effective in large vessels due to their persistence of flow currents. Paddles are used in slow or moderately sped vessels, whereas turbines are used over a wide range of viscosities.

9. Power consumption of agitators is a function of ________
a) Impeller used
b) Volumetric flow rate
c) Volumetric flow rate and Kinetic Energy
d) Kinetic Energy
Answer: c
Clarification: The power consumption of agitators is a function of both, the volumetric flow rate inside the vessel and the kinetic energy. It does not depend on the type of Impeller used for the process.

10. How can swirling be prevented in agitated vessels?
a) By reducing the power provided
b) By the use of turbines
c) By the use of Baffles
d) By lowering the shaft
Answer: c
Clarification: Swirling is a hinderance in agitated vessels and can be prevented by using Baffles appropriately, along with the turbines according to the viscosity of the fluid. Reducing the power in the system will only result in reducing the amount of agitation and the lowering of the shaft will result in unequal distribution of the fluid currents.

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