Manufacturing Engineering Multiple Choice Questions on “Heat Transfer-1”.
1. Rate of heat flow in conduction.
a) Is directly proportional to temperature gradient
b) Is inversely proportional to temperature gradient
c) Does not depend on temperature gradient
d) Does not depend on temperature gradient & inversely proportional to temperature gradient
Answer: a
Clarification: In conduction, heat transfer rate per unit area is proportional to a temperature gradient. Fourier’s law of conduction describes it as: q = -kA (frac{∂T}{∂x}), where q = heat transfer rate, (frac{∂T}{∂x}) = temperature gradient, k = thermal conductivity and the negative sign indicates heat flows downhill in temperature scale.
2. Thermal conductivity of silver in W/m-K is near about ___________
a) 210
b) 310
c) 410
d) 510
Answer: c
Clarification: Thermal conductivity of silver is nearly about 430 W/m-K at room temperature, for other materials, thermal conductivity values are tabulated below.
| S.No. | Material | K, W/m-K |
|---|---|---|
| 1. | Diamond | 2300 |
| 2. | Silver | 430 |
| 3. | Copper | 400 |
| 4. | Gold | 320 |
| 5. | Aluminium | 240 |
| 6. | Iron | 80 |
| 7. | Glass | 0.8 |
| 8. | Brick | 0.7 |
| 9. | Water | 0.61 |
| 10. | Wood | 0.17 |
| 11. | Helium | 0.15 |
| 12. | Air | 0.026 |
3. Thermal conductivity of copper in W/m-K is near about ___________
a) 210
b) 385
c) 485
d) 510
Answer: b
Clarification: Thermal conductivity of silver is nearly about 400 W/m-K at room temperature.
4. Thermal conductivity of aluminum in W/m-K is near about ___________
a) 202
b) 302
c) 410
d) 502
Answer: a
Clarification: Thermal conductivity of silver is nearly about 240 W/m-K at room temperature.
5. Which of the following is also known as transport property?
a) Pressure
b) Thermal conductivity
c) Resistance
d) Electrical conductivity
Answer: b
Clarification: Thermal conductivity of material is also known as transport property. It is an intrinsic property of a material which relates its ability to conduct heat. Heat transfer by conduction involves the transfer of energy within a material without any motion of the material as a whole.
6. With the use of thermal grease contact resistance will?
a) Increase
b) Decrease
c) Remains constant
d) First increases and then decreases
Answer: d
Clarification: Thermal grease reduces contact resistance. Silicon oil is thermal grease which decreases contact resistance.
7. Silicon oil applied between two contact surfaces will?
a) Increase contact resistance
b) Decrease contact resistance
c) Increase gap void
d) Does not depend upon contact resistance
Answer: b
Clarification: Silicone oil can act as a highly effective lubricant for sliding microelectromechanical system (MEMS) surfaces, increasing operational lifetime for devices with interacting surfaces, thus degrading electrical contact resistance.
8. When temperature of mercury liquid increases, its thermal conductivity?
a) Decreases
b) Increase
c) Remains constant
d) First increases and then decreases
Answer: a
Clarification: Thermal conductivity of liquid is inversely proportional to temperature. When temperature of mercury liquid increases, its thermal conductivity decreases.
9. When molecular weight of mercury liquid increases, its thermal conductivity?
a) Decreases
b) Increase
c) Remains constant
d) First increases and then decreases
Answer: a
Clarification: Molecular weight of liquid is inversely proportional to temperature. Thermal conductivity of liquid is inversely proportional to temperature.
10. Thermal conductivity of diamond is more than that of glass. It is because ___________
a) diamond has crystalline structure
b) glass has non crystalline structure
c) diamond and glass both have crystalline structure
d) diamond has amorphous structure
Answer: a
Clarification: Crystalline structures have more thermal conductivity due to lattice vibration. Thermal conductivity of liquid is inversely proportional to temperature.