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Heat & Mass Transfer MCQ Solved Paper for RRB ALP

Thursday 9th of March 2023

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1. 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
2. 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
3. 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
4. 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
5. 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.Cmin/U
B. U/A.Cmin
C. A.U.Cmin
D. A.U/Cmin
Answer : D
6. Planck's law holds good for
A. Black bodies
B. Polished bodies
C. All coloured bodies
D. All of the above
Answer : A
7. Cork is a good insulator because it has
A. Free electrons
B. Atoms colliding frequency
C. Low density
D. Porous body
Answer : D
8. In heat transfer, conductance equals conductivity (kcal/hr/sq.m/ °C/cm) divided by
A. Hr (time)
B. Sq. m (area)
C. °C (temperature)
D. K.cal (heat)
Answer : D
9. 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
10. Metals are good conductors of heat because
A. Their atoms collide frequently
B. Their atoms are relatively far apart
C. They contain free electrons
D. They have high density
Answer : A
11. According to Stefan's law, the total radiation from a black body per second per unit area is proportional to
A. Absolute temperature
B.
C. T?
D. T
Answer : D
12. The insulation ability of an insulator with the presence of moisture would
A. Increase
B. Decrease
C. Remain unaffected
D. May increase/decrease depending on temperature and thickness of insulation
Answer : B
13. The unit of Stefan-Boltzmann constant is
A. Watt/mK
B. Watt/m²K²
C. Watt/m²K4
D. Watt/mK²
Answer : C
14. The concept of overall coefficient of heat transfer is used in heat transfer problems of
A. Conduction
B. Convection
C. Radiation
D. Conduction and convection
Answer : D
15. The heat transfer from a hot body to a cold body is directly proportional to the surface area and difference of temperatures between the two bodies. This statement is called
A. First law of thermodynamics
B. Newton's law of cooling
C. Newton's law of heating
D. Stefan's law
Answer : B
16. Unit of thermal diffusivity is
A. m²/hr
B. m²/hr °C
C. kcal/m² hr
D. kcal/m. hr °C
Answer : A
17. A grey body is one whose absorptivity
A. Varies with temperature
B. Varies with the wave length of incident ray
C. Varies with both
D. Does not vary with temperature and wave length of the incident ray
Answer : D
18. A grey body is one whose absorptivity
A. Varies with temperature
B. Varies with wavelength of the incident ray
C. Is equal to its emissivity
D. Does not vary with temperature and. wavelength of the incident ray
Answer : C
19. 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
20. 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
21. An ordinary passenger aircraft requires a cooling system of capacity.
A. 2 TR
B. 4 TR
C. 8 TR
D. 10 TR
Answer : C
22. Thermal diffusivity of a substance is given by (where h = Thermal diffusivity, ? = Density of substance, S = Specific heat, and k = Thermal conductivity)
A. h = k/ ?S
B. h = ?S/k
C. h = S/?k
D. h = k?/S
Answer : A
23. 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
24. 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
25. The unit of overall coefficient of heat transfer is
A. W/m²K
B. W/m²
C. W/mK
D. W/m
Answer : A
26. 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
27. When absorptivity (?) = 1, reflectivity (?) = 0 and transmissivity (?) = 0, then the body is said to be a
A. Black body
B. Grey body
C. Opaque body
D. White body
Answer : A
28. 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
29. 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
30. Upto the critical radius of insulation,
A. Added insulation will increase heat loss
B. Added insulation will decrease heat loss
C. Convective heat loss will be less than conductive heat loss
D. Heat flux will decrease
Answer : A
31. 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
32. The radiation emitted by a black body is known as
A. Black radiation
B. Full radiation
C. Total radiation
D. All of these
Answer : D
33. 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
34. The unit of overall coefficient of heat transfer is
A. kcal/m²
B. kcal/hr °C
C. kcal/m² hr °C
D. kcal/m hr °C
Answer : C
35. Heat transfer by radiation mainly depends upon
A. Its temperature
B. Nature of the body
C. Kind and extent of its surface
D. All of the above
Answer : D
36. The value of the wave length for maximum emissive power is given by
A. Kirchhoff's law
B. Stefan's law
C. Wines law
D. Planck's law
Answer : C
37. 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
38. Free convection flow depends on
A. Density
B. Coefficient of viscosity
C. Gravitational force
D. All of these
Answer : D
39. Which of the following is a case of steady state heat transfer?
A. I.C. engine
B. Air preheaters
C. Heating of building in winter
D. None of the above
Answer : D
40. Stefan Boltzmann law is applicable for heat transfer by
A. Conduction
B. Convection
C. Radiation
D. Conduction and radiation combined
Answer : C
41. Thermal conductivity of solid metals with rise in temperature normally
A. Increases
B. Decreases
C. Remain constant
D. May increase or decrease depending on temperature
Answer : B
42. Thermal conductivity of water at 20°C is of the order of
A. 0.1
B. 0.23
C. 0.42
D. 0.51
Answer : D
43. The heat of sun reaches to us according to
A. Conduction
B. Convection
C. Radiation
D. None of these
Answer : C
44. According t Prevost theory of heat exchange
A. It is impossible to transfer heat from low temperature source to t high temperature source
B. Heat transfer by radiation requires no medium
C. All bodies above absolute zero emit radiation
D. Heat transfer in most of the cases takes place by combination of conduction, convection and radiation
Answer : C
45. Fouling factor is used
A. In heat exchanger design as a safety factor
B. In case of Newtonian fluids
C. When a liquid exchanges heat with a gas
D. None of the above
Answer : A
46. Total emissivity of polished silver compared to black body is
A. Same
B. Higher
C. More or less same
D. Very much lower
Answer : D
47. 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
48. 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
49. If the temperature of a solid surface changes from 27°C to 627°C, then its emissive power changes in the ratio of
A. 6
B. 9
C. 27
D. 81
Answer : D
50. The rate of energy emission from unit surface area through unit solid angle, along a normal to the surface, is known as
A. Emissivity
B. Transmissivity
C. Reflectivity
D. Intensity of radiation
Answer : D

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