Heat & Mass Transfer MCQ Solved Paper for SSC GD

1. 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

2. 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

3. 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

4. 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

5. In counter current flow heat exchanger, the logarithmic temperature difference between the fluids is ________ as compared to parallel flow heat exchanger.
A. Same
B. Less
C. Greater
D. None of these
Answer : C

6. The time constant of a thermocouple is
A. The time taken to attain the final temperature to be measured
B. The time taken to attain 50% of the value of initial temperature difference
C. The time taken to attain 63.2% of the value of initial temperature difference
D. Determined by the time taken to reach 100°C from 0°C
Answer : C

7. Fourier's law of heat conduction gives the heat flow for
A. Irregular surfaces
B. Nonuniform temperature surfaces
C. One dimensional cases only
D. Two dimensional cases only
Answer : C

8. The ratio of the emissive power and absorptive power of all bodies is the same and is equal to the emissive power of a perfectly black body. This statement is known as
A. Wien's law
B. Stefan's law
C. Kirchhoff's law
D. Planck's law
Answer : C

9. 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

10. 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

11. Which of the following has maximum value of thermal conductivity?
A. Aluminium
B. Steel
C. Brass
D. Copper
Answer : A

12. 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

13. 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

14. Emissivity of a white polished body in comparison to a black body is
A. Higher
B. Lower
C. Same
D. Depends upon the shape of body
Answer : B

15. 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

16. 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

17. Thermal conductivity of wood depends on
A. Moisture
B. Density
C. Temperature
D. All of the above
Answer : D

18. 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

19. 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

20. 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

21. The process of heat transfer from one particle of the body to another by the actual motion of the heated particles, is called
A. Conduction
B. Convection
C. Radiation
D. None of these
Answer : B

22. 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

23. A composite slab has two layers of different materials with thermal conductivities k? and k?. If each layer has the same thickness, then the equivalent thermal conductivity of the slab will be
A. k? k?
B. (k? + k?)
C. (k? + k?)/ k? k?
D. 2 k? k?/ (k? + k?)
Answer : D

24. 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

25. 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

26. The amount of radiation mainly depends on
A. Nature of body
B. Temperature of body
C. Type of surface of body
D. All of the above
Answer : D

27. 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

28. 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

29. When heat is transferred from hot body to cold body, in a straight line, without affecting the intervening medium, it is referred as heat transfer by
A. Conduction
B. Convection
C. Radiation
D. Conduction and convection
Answer : C

30. The heat transfer by conduction through a thick sphere is given by
A. Q = 2?kr₁ r₂ (T₁ - T₂)/ (r₂ - r₁)
B. Q = 4?kr₁ r₂ (T₁ - T₂)/ (r₂ - r₁)
C. Q = 6?kr₁ r₂ (T₁ - T₂)/ (r₂ - r₁)
D. Q = 8?kr₁ r₂ (T₁ - T₂)/ (r₂ - r₁)
Answer : B

31. 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

32. 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

33. 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

34. 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

35. 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

36. 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

37. The emissive power of a body depends upon its
A. Temperature
B. Wave length
C. Physical nature
D. All of the above
Answer : D

38. 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

39. 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

40. Film coefficient is defined as Inside diameter of tube
A. Equivalent thickness of film
B. Thermal conductivity Equivalent thickness of film Specific heat × Viscosity
C. Thermal conductivity Molecular diffusivity of momentum Thermal diffusivity
D. Film coefficient × Inside diameter Thermal conductivity
Answer : B

41. The ratio of the thickness of thermal boundary layer to the thickness of hydrodynamic boundary layer is equal to (Prandtl number) n, where n is equal to
A. -1/3
B. -2/3
C. 1
D. -1
Answer : A

42. 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

43. 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

44. Temperature of steam at around 540°C can be measured by
A. Thermometer
B. Thermistor
C. Thermocouple
D. None of these
Answer : C

45. 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

46. 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

47. Heat transfer in liquid and gases takes place by
A. Conduction
B. Convection
C. Radiation
D. Conduction and convection
Answer : B

48. The total radiation from a black body per second per unit area is ________ fourth power of the absolute temperature. This statement is known as Stefan Boltzmann law.
A. Equal to
B. Directly proportional to
C. Inversely proportional to
D. None of these
Answer : B

49. Reynolds number is the ratio of
A. Energy transferred by convection to that by conduction
B. Kinematic viscosity to thermal diffusivity
C. Inertia force to viscous force
D. None of the above
Answer : C

50. According to Dalton's law of partial pressures, (where pb = Barometric pressure, pa = Partial pressure of dry air, and pv = Partial pressure of water vapour)
A. Pb = pa - pv
B. Pb = pa + pv
C. Pb = pa × pv
D. Pb = pa/pv
Answer : B