Engineering Questions with Answers - Multiple Choice Questions
Manufacturing Engineering – Heat Transfer-1
1 - Question
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
View Answer
Explanation: In conduction, heat transfer rate per unit area is proportional to a temperature gradient. Fourier’s law of conduction describes it as: q = -kA ∂T∂x, where q = heat transfer rate, ∂T∂x = temperature gradient, k = thermal conductivity and the negative sign indicates heat flows downhill in temperature scale.
2 - Question
Thermal conductivity of silver in W/m-K is near about ___________
a) 210
b) 310
c) 410
d) 510
View Answer
Explanation: 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 - Question
Thermal conductivity of copper in W/m-K is near about ___________
a) 210
b) 385
c) 485
d) 510
View Answer
Explanation: Thermal conductivity of silver is nearly about 400 W/m-K at room temperature.
4 - Question
Thermal conductivity of aluminum in W/m-K is near about ___________
a) 202
b) 302
c) 410
d) 502
View Answer
Explanation: Thermal conductivity of silver is nearly about 240 W/m-K at room temperature.
5 - Question
Which of the following is also known as transport property?
a) Pressure
b) Thermal conductivity
c) Resistance
d) Electrical conductivity
View Answer
Explanation: 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 - Question
With the use of thermal grease contact resistance will?
a) Increase
b) Decrease
c) Remains constant
d) First increases and then decreases
View Answer
Explanation: Thermal grease reduces contact resistance. Silicon oil is thermal grease which decreases contact resistance.
7 - Question
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
View Answer
Explanation: 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 - Question
When temperature of mercury liquid increases, its thermal conductivity?
a) Decreases
b) Increase
c) Remains constant
d) First increases and then decreases
View Answer
Explanation: Thermal conductivity of liquid is inversely proportional to temperature. When temperature of mercury liquid increases, its thermal conductivity decreases.
9 - Question
When molecular weight of mercury liquid increases, its thermal conductivity?
a) Decreases
b) Increase
c) Remains constant
d) First increases and then decreases
View Answer
Explanation: Molecular weight of liquid is inversely proportional to temperature. Thermal conductivity of liquid is inversely proportional to temperature.
10 - Question
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
View Answer
Explanation: Crystalline structures have more thermal conductivity due to lattice vibration. Thermal conductivity of liquid is inversely proportional to temperature.