Heat & Mass Transfer MCQ Solved Paper for IBPS RRB

1. The highest thermal diffusivity is of
A. Iron
B. Lead
C. Concrete
D. Wood
Answer : B

2. The process of heat transfer from one particle of the body to another is called conduction, when the particles of the body
A. Move actually
B. Do not move actually
C. Affect the intervening medium
D. Does not affect the intervening medium
Answer : B

3. 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

4. In regenerator type heat exchanger, heat transfer takes place by
A. Direct mixing of hot and cold fluids
B. A complete separation between hot and cold fluids
C. Flow of hot and cold fluids alternately over a surface
D. Generation of heat again and again
Answer : C

5. A steam pipe is to be insulated by two insulating materials put over each other. For best results
A. Better insulation should be put over pipe and better one over it
B. Inferior insulation should be put over pipe and better one over it
C. Both may be put in any order
D. Whether to put inferior OIL over pipe or the better one would depend on steam temperature
Answer : A

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

7. 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

8. Fourier's law of heat conduction is (where Q = Amount of heat flow through the body in unit time, A = Surface area of heat flow, taken at right angles to the direction of heat flow, dT = Temperature difference on the two faces of the body, dx = Thickness of the body, through which the heat flows, taken along the direction of heat flow, and k = Thermal conductivity of the body)
A. k. A. (dT/dx)
B. k. A. (dx/dT)
C. k. (dT/dx)
D. k. (dx/dT)
Answer : A

9. The unit of overall coefficient of heat transfer is
A. W/m²K
B. W/m²
C. W/mK
D. W/m
Answer : A

10. 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

11. 40% of incident radiant energy on the surface of a thermally transparent body is reflected back. If the transmissivity of the body be 0.15, then the emissivity of surface is
A. 0.45
B. 0.55
C. 0.40
D. 0.75
Answer : A

12. According to Wien's law, the wavelength corresponding to maximum energy is proportion to
A. Absolute temperature (T)
B. I²
C. F
D. T
Answer : A

13. Thermal diffusivity is
A. A dimensionless parameter
B. Function of temperature
C. Used as mathematical model
D. A physical property of the material
Answer : D

14. The ratio of the energy absorbed by the body to total energy falling on it is called
A. Absorptive power
B. Emissive power
C. Absorptivity
D. Emissivity
Answer : A

15. In free convection heat transfer transition from laminar to turbulent flow is governed by the critical value of the
A. Reynold's number
B. Grashoff's number
C. Reynold's number, Grashoff's number
D. Prandtl number, Grashoff's number
Answer : D

16. Thermal conductivity of air at room temperature in kcal/m hr °C is of the order of
A. 0.002
B. 0.02
C. 0.01
D. 0.1
Answer : B

17. Two balls of same material and finish have their diameters in the ratio of 2: 1 and both are heated to same temperature and allowed to cool by radiation. Rate of cooling by big ball as compared to smaller one will be in the ratio of
A. 1 : 1
B. 2 : 1
C. 1 : 2
D. 4 : 1
Answer : C

18. In heat exchangers, degree of approach is defined as the difference between temperatures of
A. Cold water inlet and outlet
B. Hot medium inlet and outlet
C. Hot medium outlet and cold water inlet
D. Hot medium outlet and cold water outlet
Answer : D

19. 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

20. LMTD in case of counter flow heat exchanger as compared to parallel flow heat exchanger is
A. Higher
B. Lower
C. Same
D. Depends on the area of heat exchanger
Answer : A

21. Absorptivity of a body will be equal to its emissivity
A. At all temperatures
B. At one particular temperature
C. When system is under thermal equilibrium
D. At critical temperature
Answer : C

22. 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

23. The heat is transferred by conduction, convection and radiation in
A. Melting of ice
B. Boiler furnaces
C. Condensation of steam in condenser
D. None of these
Answer : B

24. 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

25. The logarithmic mean temperature difference (t_m) is given by (where ?t₁ and ?t₂ are temperature differences between the hot and cold fluids at entrance and exit)
A. t_m = (?t₁ - ?t₂)/ log_e (?t₁/?t₂)
B. t_m = log_e (?t₁/?t₂)/ (?t₁ - ?t₂)
C. t_m = t_m = (?t₁ - ?t₂) log_e (?t₁/?t₂)
D. t_m = log_e (?t₁ - ?t₂)/ ?t₁/?t₂
Answer : A

26. Unit of thermal conductivity in M.K.S. units is
A. K cal/kg m² °C
B. K cal m/hr m² °C
C. K cal/hr m² °C
D. K calm/hr °C
Answer : B

27. 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

28. Fourier's law of heat conduction is valid for
A. One dimensional cases only
B. Two dimensional cases only
C. Three dimensional cases only
D. Regular surfaces having non-uniform temperature gradients
Answer : A

29. Thermal diffusivity of a substance is
A. Directly proportional to the thermal conductivity
B. Inversely proportional to density of substance
C. Inversely proportional to specific heat
D. All of the above
Answer : D

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

31. 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

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

33. If the energy radiated per second per sq. cm. of the surface for wave lengths lying between ?, and ? + d? is represented by (e?.d?), then e? is called
A. Absorptive power
B. Emissive power
C. Emissivity
D. None of these
Answer : B

34. Which of the following statement is wrong?
A. The heat transfer in liquid and gases takes place according to convection.
B. The amount of heat flow through a body is dependent upon the material of the body.
C. The thermal conductivity of solid metals increases with rise in temperature
D. Logarithmic mean temperature difference is not equal to the arithmetic mean temperature difference.
Answer : C

35. According to Stefan's law, the total radiation from a black body per second per unit area is proportional to
A. Absolute temperature
B. T²
C. T?
D. T
Answer : D

36. 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

37. 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

38. 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

39. According to Kirchoff's law, the ratio of emissive power to absorptivity for all bodies is equal to the emissive power of a
A. Grey body
B. Brilliant white polished body
C. Red hot body
D. Black body
Answer : D

40. In a shell and tube heat exchanger, baffles are provided on the shell side to
A. Improve heat transfer
B. Provide support for tubes
C. Prevent stagnation of shell side fluid
D. All of these
Answer : D

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

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

43. A designer chooses the values of fluid flow rates and specific heats in such a manner that the heat capacities of the two fluids are equal. A hot fluid enters the counter flow heat exchanger at 100° C and leaves at 60° C. A cold fluid enters the heat exchanger at 40° C. The mean temperature difference between the two fluids is
A. 20°C
B. 40°C
C. 60°C
D. 66.7°C
Answer : A

44. In free convection heat transfer, Nusselt number is function of
A. Grashoff number and Reynold number
B. Grashoff number and Prandtl number
C. Prandtl number and Reynold number
D. Grashoff number, Prandtl number and Reynold number
Answer : B

45. A heat exchanger with heat transfer surface area A and overall heat transfer coefficient U handles two fluids of heat capacities Cmax and Cmin. The number of transfer units (NTU) used in the analysis of heat exchanger is specified as
A. A.C_min/U
B. U/A.C_min
C. A.U.C_min
D. A.U/C_min
Answer : D

46. Wiens law states that the wave length corresponding to ________ is proportional to the absolute temperature.
A. Minimum energy
B. Maximum energy
C. Both (A) and (B)
D. None of these
Answer : B

47. 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

48. In convection heat transfer from hot flue gases to water tube, even though flow may be turbulent, a laminar flow region (boundary layer of film) exists close to the tube. The heat transfer through this film takes place by
A. Convection
B. Radiation
C. Conduction
D. Both convection and conduction
Answer : C

49. 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

50. 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