Mechanical Engineering mcq

Mechanical Engineering mcq 

Subject:- Heat Transfer 

1. Unit of the rate of heat transfer is

a) Joule

b) Newton

c) Pascal

d) Watt

Answer: d

Explanation: Unit of heat transfer is Joule but the rate of heat transfer is joule per second i.e. watt.

2. Which of the following is an example of steady state heat transfer?

a) Boilers and turbines

b) Cooling of I.C engine

c) Chilling effect of cold wind on a warm body

d) Electric bulb cools down by the surrounding atmosphere

Answer: d

Explanation: System is a perfect black body.

3. Heat transfer takes place according to which law?

a) Newton’s law of cooling

b) Second law of thermodynamics

c) Newton’s second law of motion

d) First law of thermodynamics

Answer: b

Explanation: Second law states about heat transfer between source and sink.

4. How many types of convection process are there?

a) One

b) Three

c) Four

d) Two

Answer: b

Explanation: Forced, natural and mixed convection.

5. Which one of the following forms of water have the highest value of thermal conductivity?

a) Boiling water

b) Steam

c) Solid ice

d) Melting ice

View Answer

Answer: c

6. A composite wall generally consists of

a) One homogenous layer

b) Multiple heterogeneous layers

c) One heterogeneous layer

d) Multiple homogenous layers

Answer: b

Explanation: Walls of houses where bricks are given a layer of plaster on either side.

7. The extended surface used for the enhancement of heat dissipation is

a) Convective coefficient

b) Fourier number

c) Fin

d) No finned surface

Answer: c

8. To have high effectiveness of fins

A. fin must be thick and closely spaced

B. fin must be thin and closely spaced

C.fin must be thick and widely spaced

D. fin must be thin and widely spaced

Correct Answer : B

9. Ideal shape of fin is

A. Trapezoidal

B. Parabolic

C. Rectangular

D. circular

Correct Answer : B

Ideal shape of fin is parabolic but due to design constraints trapezoidal shape is used in practical application.

10. Grashof number is

A. dimensionless number 

B. ratio of buoyancy 

C. applied in convection 

D. all of above 

Correct Answer : D

Grashof number is dimensionless number used in fluid mechanics and heat transfer which measure ratio of buoyancy normally used in conventional heat transfer method.

11. Automobile radiator is a heat exchanger of ________ type. 

A. Counter flow

B. Parallel flow 

C. Cross flow

D. Regenerator 

Correct Answer : C

A tube bundle carries a heating or cooling fluid (either gas or liquid), normally perpendicular to a gas flow which passes over the tubes and allows heat to be transferred between the fluids.

12. Navier Strokes equation represents the conservation of 

A. energy

B. mass

C. pressure

D. momentum 

Correct Answer : D

Navier Strokes equation is based on conservation of momentum. 

These equations describe how the velocity, pressure, temperature, and density of a moving fluid are related. 

13. NTU method is used to calculate: 

A. Rate of heat transfer 

B. Rate of liquid flow 

C. Rate of conduction heat 

D. Rate of radiation 

Correct Answer : A

The Number of Transfer Units is a method used to calculate the rate of heat transfer in heat exchanger when there is insufficient information to calculate the Log-Mean Temperature Difference (LMTD). 

14. The material having least thermal conductivity ________.

A. Glass wood

B. Asbestos

C. Freon-12

D. Air

Correct Answer : C.

15. What does NTU indicate? 

A. Effectiveness of heat exchanger 

B. Efficiency of heat exchanger 

C. Size of heat exchanger 

D. Temperature drop in heat exchanger. 

Correct Answer : C

16. Dominant heat transfer in liquid and gases take place by _____. 

A. conduction 

B. convection 

C. radiation 

D. conduction and convection both 

Correct Answer : B

Heat can be transferred from one place to another by three methods: conduction in solids, convection of fluids (liquids or gases), and radiation through anything that will allow radiation to pass. The method used to transfer heat is usually the one that is the most efficient.

In the question it was asked about dominant, so possible mode of heat transfer in fluids(liquids & gases) is convection.

17. Which one is true for an opaque body?

A. Transmissivity is zero

B. Reflectivity is zero

C. Absorptivity is zero

D. Reflectivity is unity

Correct Answer : A

For the opaque body, sum of absorptivity and reflectivity is unity.

18. A body that reflects all the incident thermal radiations is called a

A. Opaque body

B. Gases

C. Black body

D. Specular body

Correct Answer : D

In this case reflection is regular. For such bodies reflectivity is unity and transmissivity is equal to zero.

19. At thermal equilibrium :

A. reflectvity will become zero

B. Absorptivity is lesser than emissivity

C. Absorptivity is equal to emissivity

D. Sum of absorptivity and emissivity is unity

Correct Answer : C

as per the kirchoff law, At thermal equilibrium, absorptivity is equal to emissivity.

20. Planck’s law holds good for:

A. Black bodies

B. Polished bodies

C. All colored bodies

D. All of the above

Correct Answer : A

Planck’s law states that the monochromatic emissive power of a black body is dependent on both absolute temperature of blackbody and also on wavelength of energy emitted by the body.

21. As the wave length Increases, the monochromatic emissivity of the grey body 

A. Increase 

B. Decrease 

C. Independent of wavelength 

D. First increase then decrease 

Correct Answer : C

Grey surface is that surface in which monochromatic emissivity is independent of wavelength

22. In radiative heat transfer, a gray surface is one ___________. 

A. Which appears gray to the eye 

B. Whose emissivity is independent of wavelength 

C. Which has reflectivity equal to zero 

D. Which appears equally bright from all directions 

Correct Answer : B

23. Heat is transferred from an insulated pipe to the surrounding still air by ______. 

A. Conduction

B. Convection 

C. Radiation

D. All options are correct 

Correct Answer : C

There will be no heat transfer from the surface as heat transfer by conduction and convection always requires contact surface area, as the pipe is insulated heat transfer from the surface will not take place.

But radiation heat transfer takes place even in vacuum, that even after insulation there will be some radiation heat transfer.

24. Heat transfer by radiation mainly depends upon _____________. 

A. its temperature 

B. nature of the body 

C. kind and extent of its surface 

D. All options are correct 

Correct Answer : A

25. Which surface will have the least emissivity? 

A. Smooth glass 

B. Plaster 

C. Aluminum foil 

D. Concrete 

Correct Answer : C

Emissivity is a measure of a material’s radiating efficiency. An emissivity of 1.00 implies that the material is 100% efficient at radiating energy. 

26. The process of heat transfer from a hot body to a cold body is straight line, without affecting the intervening medium, is known as ________. 

A. Conduction

B. Convection 

C. Radiation

D. All options are correct 

Correct Answer : C

Heat is carried through the atomic vibration & electron motion.

Electromagnetic waves propagate rectilinearly, like light. 

27. Heat is transferred from an electric bulb by ___________. 

A. Conduction

B. Convection 

C. Radiation

D. All options are correct 

Correct Answer : D

(i) filament is heated due to conduction 

(ii) Then there’s convection, which drives a flow inside the bulb transferring the heat from the filament throughout the bulb via the movement of fluids (in this case that’s argon gas). 

(iii) but finally in last, heat is transferred from an electric bulb by radiation.

28. The ratio of the energy absorbed by the body to total energy falling on it is called _____. 

A. absorptive power

B. emissive power 

C. emissivity

D. None of these 

Correct Answer : A