This set of Manufacturing Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Fluid Flow and Heat Transfer”.
1. The flow of fluid which is highly chaotic is called as?
d) Irrotational flow
Explanation: 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 ____________
Explanation: 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
Explanation: 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?
d) either higher or lower
Explanation: 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
Explanation: 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 ____________
d) refractory brick
Explanation: 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)
Explanation: Thermal conductivity of values at room temperature are tabulated below:
|S.No.||Material||Thermal Conductivity (W/m-K)|
8. A copper block and an air mass block having similar dimensions are subjected to symmetrical heat transfer from one face of each block. The other face of the block will be reaching the same temperature at a rate is?
a) Faster in air block
b) Faster in copper block
c) Equal in air as well as copper block
d) Cannot be predicted with the given information
Explanation: Copper has a thermal conductivity of 400 W/m-K and air has an value of 0.026 W/m-K.
9. Consider the following statements:
The Fourier heat conduction equation Q = -kA(dT/dx) presumes
i. Steady-state conditions
ii. Constant value of thermal conductivity.
iii. Uniform temperatures at the wall surfaces
iv. One-dimensional heat flow.
Which of the above statements are correct?
a) (i), (ii) and (iii) are correct
b) (i), (ii) and (iv) are correct
c) (ii), (iii) and (iv) are correct
d) (i), (iii) and (iv) are correct
Explanation: Thermal conductivity may constant or variable.
10. The outer surface of a long cylinder is maintained at constant temperature. The cylinder does not have any heat source. The temperature in the cylinder will?
a) Increase linearly with radius
b) Decrease linearly with radius
c) Be independent of radius
d) Vary logarithmically with radius
Explanation: In case of cylinder, in Q = -kA (dT/dr), thus indicating the logarithmic change.
11. For conduction through a spherical wall with constant thermal conductivity and with inner side temperature greater than outer wall temperature, (one dimensional heat transfer), what is the type of temperature distribution?
Explanation: Temp distribution would be t – t1.
Sanfoundry Global Education & Learning Series – Manufacturing Engineering.
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