Manufacturing Engineering Multiple Choice Questions on “Fluid Flow and Heat Transfer”.
1. The flow of fluid which is highly chaotic is called as?
a) Laminar
b) Turbulence
c) Reynolds
d) Irrotational flow
Answer: b
Clarification: Turbulent flow is chaotic. However, not all chaotic flows are turbulent. Turbulent flow is characterized by the irregular movement of particles of the fluid. In contrast to laminar the fluid does not flow in parallel layers, the lateral mixing is very high, and there is a disruption between the layers. Turbulence is also characterized by recirculation, eddies, and apparent randomness, in other sense, in turbulent flow-the speed of the fluid at a point is continuously undergoing changes in both magnitude and direction.
2. The capability of molten metal to fill mold cavities is called ____________
a) viscosity
b) fluidity
c) turbulence
d) velocity
Answer: b
Clarification: Fluidity is the property of a fluid which allows fluid to flow. In general understanding, one can say, the fluidity is inversely proportional to viscosity. Factors affecting fluidity in casting are as follows.
i. Modulus: fluidity length increases as the modulus (volume/surface area) of the casting increases
ii. Section thickness: larger thickness of section results in higher fluidity
iii. Heat transfer coefficient: a reduction in the rate of heat transfer will increase fluidity
iv. Superheating: the temperature increment above the melting point increases fluidity
v. Mould temperature: higher mould temperature increases fluidity
vi. Pouring rate: lower pouring rates decrease fluidity because of larger cooling.
3. The liquid metal reduces its fluidity mainly due to?
a) high viscosity
b) high friction factor
c) high surface tension
d) high turbulence
Answer: c
Clarification: A high surface tension of the liquid metal reduces fluidity. Because of this, oxide films on the surface of the molten metal have a significant adverse effect on fluidity.
4. The slower the rate of pouring molten metal into the mold, the nature of fluidity will be?
a) lower
b) higher
c) constant
d) either higher or lower
Answer: a
Clarification: The slower the rate of pouring molten metal into the mold, the lower is the fluidity because of the higher rate of cooling when poured slowly.
5. With an increase in the thickness of insulation around a circular pipe, heat loss to surrounding due to ____________
a) convection increase, while that the due to conduction decreases
b) convection decrease, while that due to conduction increases
c) convection and conduction decreases
d) convection and conduction increases
Answer: b
Clarification: By increasing the thickness of insulation, the convection heat transfer co-efficient decreases and heat loss by the convection also decreases. These both cases are limited for the critical thickness of insulation.
6. For a given heat flow and for the same thickness, the temperature drop across the material will be maximum for ____________
a) copper
b) steel
c) glass-wool
d) refractory brick
Answer: c
Clarification: Q = -kA (dT/dx)
Qdx/A = -kdT
therefore, kdT = constant or dT ∞ 1/k.
7. In descending order of magnitude, the thermal conductivity of:
i. Pure iron,
ii. Liquid water,
iii. Saturated water vapour, and
iv. Pure aluminium
can be arranged as?
a) (i), (ii), (iii) and (iv)
b) (ii), (iii), (i) and (iv)
c) (iv), (i), (ii) and (iii)
d) (iv), (iii), (ii) and (i)