1000+ Heat & Mass Transfer Multiple Choice Question Answer [Solved]

1. The concept of overall coefficient of heat transfer is used in case of heat transfer by
A. Conduction
B. Convection
C. Radiation
D. Conduction and convection
Answer : D

2. Free convection flow depends on
A. Density
B. Coefficient of viscosity
C. Gravitational force
D. All of these
Answer : D

3. The process of heat transfer from one particle of the fluid to another by the actual movement of the fluid particles caused by some mechanical means, is known as
A. Conduction
B. Free convection
C. Forced convection
D. Radiation
Answer : C

4. The use of heat exchangers is made in
A. Radiators in automobile
B. Condensers and boilers in steam plants
C. Condensers and evaporators in refrigeration and air conditioning units
D. All of the above
Answer : D

5. Log mean temperature difference in case of counter flow compared to parallel flow will be
A. Same
B. More
C. Less
D. Depends on other factors
Answer : B

6. The total emissivity power is .defined as the total amount of radiation emitted by a black body per unit
A. Temperature
B. Thickness
C. Area
D. Time
Answer : D

7. Unit of thermal diffusivity is
A. m²/hr
B. m²/hr °C
C. kcal/m² hr
D. kcal/m. hr °C
Answer : A

8. Stefan Boltzmann law is applicable for heat transfer by
A. Conduction
B. Convection
C. Radiation
D. Conduction and radiation combined
Answer : C

9. The natural convection air cooled condensers are used in
A. Domestic refrigerators
B. Water coolers
C. Room air conditioners
D. All of these
Answer : A

10. The amount of radiation mainly depends upon the
A. Nature of the body
B. Temperature of the body
C. Type of surface of the body
D. All of these
Answer : D

11. Radiation is the process of heat transfer in which heat flows from a ________, in a straight line, without affecting the intervening medium.
A. Cold body to hot body
B. Hot body to cold body
C. Smaller body to larger body
D. Larger body to smaller body
Answer : B

12. The amount of heat flow through a body by conduction is
A. Directly proportional to the surface area of the body
B. Directly proportional to the temperature difference on the two faces of the body
C. Dependent upon the material of the body
D. All of the above
Answer : D

13. The heat transfer by conduction through a thick cylinder (Q) is given by (where T? = Higher temperature, T? = Lower temperature, r? = Inside radius, r? = Outside radius, l = Length of cylinder, and k = Thermal conductivity)
A. Q = [2?lk (T? - T?)]/2.3 log (r?/r?)
B. Q = 2.3 log (r?/r?)/[2?lk (T? - T?)]
C. Q = [2? (T? - T?)]/2.3 lk log (r?/r?)
D. Q = = 2?lk/2.3 (T? - T?) log (r?/r?)
Answer : A

14. The heat transfer takes place according to
A. Zeroth law of thermodynamics
B. First law of thermodynamics
C. Second law of thermodynamics
D. Kirchhoff's law
Answer : C

15. The heat of sun reaches to us according to
A. Conduction
B. Convection
C. Radiation
D. None of these
Answer : C

16. Cork is a good insulator because it has
A. Free electrons
B. Atoms colliding frequency
C. Low density
D. Porous body
Answer : D

17. In case of liquids and gases, the heat transfer takes place according to
A. Conduction
B. Convection
C. Radiation
D. None of these
Answer : B

18. Thermal conductivity of glass wool varies from sample to sample because of variation in
A. Composition
B. Density
C. Porosity
D. All of the above
Answer : D

19. The critical temperature is the temperature
A. Below which a gas does not obey gas laws
B. Above which a gas may explode
C. Below which a gas is always liquefied
D. Above which a gas will never liquefied
Answer : D

20. Thermal conductivity of a material may be defined as the
A. Quantity of heat flowing in one second through one cm cube of material when opposite faces ^re maintained at a temperature difference of 1°C
B. Quantity of heat flowing in one second through a slab of the material of area one cm square, thickness 1 cm when its faces differ in temperature by 1°C
C. Heat conducted in unit time across unit area through unit thickness when a temperature difference of unity is maintained between opposite faces
D. All of the above
Answer : D

21. The thermal diffusivities for solids are generally
A. Less than those for gases
B. Less than those for liquids
C. More than those for liquids and gases
D. More or less same as for liquids and gases
Answer : C

22. Film coefficient is defined as the ratio of
A. Thermal conductivity to the equivalent thickness of the film of fluid
B. Temperature drop through the films of fluids to the thickness of film of fluids
C. Thickness of film of fluid to the thermal conductivity
D. Thickness of film of fluid to the temperature drop through the films of fluids
Answer : A

23. Thermal diffusivity is a
A. Function of temperature
B. Physical property of a substance
C. Dimensionless parameter
D. All of these
Answer : B

24. The automobile radiator is a heat exchanger of
A. Parallel flow type
B. Counter flow type
C. Cross flow type
D. Regenerator type
Answer : C

25. The unit of Stefan Boltzmann constant is
A. Watt/cm² °K
B. Watt/cm4 °K
C. Watt²/cm °K?
D. Watt/cm² °K?
Answer : D

26. The unit of Stefan-Boltzmann constant is
A. Watt/mK
B. Watt/m²K²
C. Watt/m²K⁴
D. Watt/mK²
Answer : C

27. A steam pipe is to be lined with two layers of insulating materials of different thermal conductivities. For the minimum heat transfer,
A. The better insulation must be put inside
B. The better insulation must be put outside
C. One could place either insulation on either side
D. One should take into account the steam temperature before deciding as to which insulation is put where
Answer : A

28. Two long parallel surfaces each of emissivity 0.7 are maintained at different temperatures and accordingly have radiation heat exchange between them. It is desired to reduce 75% of the radiant heat transfer by inserting thin parallel shields of emissivity 1 on both sides. The number of shields should be
A. One
B. Two
C. Three
D. Four
Answer : C

29. Reynolds number (RN) is given by (where h = Film coefficient, l = Linear dimension, V = Velocity of fluid, k = Thermal conductivity, t = Temperature, ? = Density of fluid, cp = Specific heat at constant pressure, and ? = Coefficient of absolute viscosity)
A. RN = hl/k
B. RN = ? cp/k
C. RN = ? V l /?
D. RN = V²/t.cp
Answer : C

30. The rate of energy transferred by convection to that by conduction is called
A. Stanton number
B. Nusselt number
C. Biot number
D. Peclet number
Answer : B

31. Which of the following has least value of conductivity?
A. Glass
B. Water
C. Plastic
D. Air
Answer : D

32. When ? is absorptivity, ? is reflectivity and ? is transmissivity, then for a diathermanous body,
A. ? = 1, ? = 0 and ? = 0
B. ? = 0, ? = 1 and ? = 0
C. ? = 0, ? = 0 and ? = 1
D. ? + ? = 1 and ? = 0
Answer : D

33. When heat is transferred by molecular collision, it is referred to as heat transfer by
A. Conduction
B. Convection
C. Radiation
D. Scattering
Answer : B

34. Planck's law holds good for
A. Black bodies
B. Polished bodies
C. All coloured bodies
D. All of the above
Answer : A

35. The process of heat transfer from one particle of the fluid to another by the actual movement of the fluid particles due to difference of density caused by temperature of the particle is known as
A. Conduction
B. Free convection
C. Forced convection
D. Radiation
Answer : B

36. The product of Reynolds number and Prandtl number is known as
A. Stanton number
B. Biot number
C. Peclet number
D. Grashoff number
Answer : C

37. In counter flow heat exchangers
A. Both the fluids at inlet (of heat exchanger where hot fluid enters) are in their coldest state
B. Both the fluids at inlet are in their hottest state
C. Both the fluids at exit are in their hottest state
D. One fluid is in hottest state and other in coldest state at inlet
Answer : B

38. An ordinary passenger aircraft requires a cooling system of capacity.
A. 2 TR
B. 4 TR
C. 8 TR
D. 10 TR
Answer : C

39. Thermal conductivity of air with rise in temperature
A. Increases
B. Decreases
C. Remain constant
D. May increase or decrease depending on temperature
Answer : A

40. The critical radius is the insulation radius at which the resistance to heat flow is
A. Maximum
B. Minimum
C. Zero
D. None of these
Answer : B

41. Depending on the radiating properties, a body will be white when
A. P = 0, x = 0 and a = 1
B. P=1, T = 0 and a = 0
C. P = 0, x = 1 and a = 0
D. X = 0, a + p = 1 Where a = absorptivity, p = reflectivity, x = transmissivity
Answer : B

42. Total heat is the heat required to
A. Change vapour into liquid
B. Change liquid into vapour
C. Increase the temperature of a liquid or vapour
D. Convert water into steam and superheat it
Answer : D

43. According to Newton's law of cooling, the heat transfer from a hot body to a cold body is
A. Directly proportional to the surface area
B. Directly proportional to the difference of temperatures between the two bodies
C. Either (A) or (B)
D. Both (A) and (B)
Answer : D

44. The most commonly used method for the design of duct size is the
A. Velocity reduction method
B. Equal friction method
C. Static regains method
D. Dual or double method
Answer : C

45. The ratio of Nusselt number and the product of Reynold's number and Prandtl number is equal to
A. Stanton number
B. Biot number
C. Peclet number
D. Grashoff number
Answer : A

46. Heat conducted through per unit area and unit thick face per unit time when temperature difference between opposite faces is unity, is called
A. Thermal resistance
B. Thermal coefficient
C. Temperature gradient
D. Thermal conductivity
Answer : D

47. The energy distribution of an ideal reflector at higher temperatures is largely in the range of
A. Shorter wavelength
B. Longer wavelength
C. Remain same at all wavelengths
D. Wavelength has nothing to do with it
Answer : A

48. In a heat exchanger with one fluid evaporating or condensing, the surface area required is least in
A. Parallel flow
B. Counter flow
C. Cross flow
D. All of these
Answer : D

49. The ratio of surface convection resistance to the internal conduction resistance is known as
A. Grashoff number
B. Biot number
C. Stanton number
D. Prandtl number
Answer : B

50. According of Kirchhoff's law
A. Radiant heat is proportional to fourth power of absolute temperature
B. Emissive power depends on temperature
C. Emissive power and absorptivity are constant for all bodies
D. Ratio of emissive power to absorptive power for all bodies is same and is equal to the emissive power of a perfectly black body.
Answer : D