Home

Heat & Mass Transfer 1000+ MCQ with answer for XAT

Thursday 9th of March 2023

Sharing is caring

Downlaod Heat & Mass Transfer MCQ PDF
1. The value of the wavelength for maximum emissive power is given by
A. Wien's law
B. Planck's law
C. Stefan's law
D. Fourier's law
Answer : A
2. 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
3. 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
4. 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
5. 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
6. 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
7. 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
8. 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
9. The value of Prandtl number for air is about
A. 0.1
B. 0.3
C. 0.7
D. 1.7
Answer : C
10. 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
11. Sensible heat is the heat required to
A. Change vapour into liquid
B. Change liquid into vapour
C. Increase the temperature of a liquid of vapour
D. Convert water into steam and superheat it
Answer : C
12. Thermal diffusivity is a
A. Function of temperature
B. Physical property of a substance
C. Dimensionless parameter
D. All of these
Answer : B
13. 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
14. Stefan Boltzmann law is applicable for heat transfer by
A. Conduction
B. Convection
C. Radiation
D. Conduction and radiation combined
Answer : C
15. 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
16. Thermal diffusivity of a substance is
A. Directly proportional to thermal conductivity
B. Inversely proportional to density of substance
C. Inversely proportional to specific heat
D. All of the above
Answer : D
17. 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
18. 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
19. 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
20. 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
21. Free convection flow depends on
A. Density
B. Coefficient of viscosity
C. Gravitational force
D. All of these
Answer : D
22. 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
23. 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
24. 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
25. 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
26. An electric cable of aluminium conductor (k = 240 W/mK) is to be insulated with rubber (k = 0.15 W/mK). The cable is to be located in air (h = 6 W/m²). The critical thickness of insulation will be
A. 25 mm
B. 40 mm
C. 160 mm
D. 800 mm
Answer : A
27. 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
28. 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
29. The emissivity for a black body is
A. 0
B. 0.5
C. 0.75
D. 1
Answer : D
30. 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
31. 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
32. 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
33. 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
34. 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
35. Heat transfer in liquid and gases takes place by
A. Conduction
B. Convection
C. Radiation
D. Conduction and convection
Answer : B
36. Heat flows from one body to other when they have
A. Different heat contents
B. Different specific heat
C. Different atomic structure
D. Different temperatures
Answer : D
37. Heat transfer takes place as per
A. Zeroth law of thermodynamics
B. First law of thermodynamic
C. Second law of the thermodynamics
D. Kirchoff's law
Answer : C
38. 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
39. 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
40. 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
41. Depending on the radiating properties, a body will be black 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 = 0 Where a = absorptivity, p = reflectivity, X = transmissivity.
Answer : A
42. The rate of heat flow through a body is Q = [kA (T? - T?)]/x. The term x/kA is known as
A. Thermal coefficient
B. Thermal resistance
C. Thermal conductivity
D. None of these
Answer : B
43. 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
44. 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
45. 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
46. According to Stefan Boltzmann law, ideal radiators emit radiant energy at a rate proportional to
A. Absolute temperature
B. Square of temperature
C. Fourth power of absolute temperature
D. Fourth power of temperature
Answer : C
47. 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
48. 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
49. An ordinary passenger aircraft requires a cooling system of capacity.
A. 2 TR
B. 4 TR
C. 8 TR
D. 10 TR
Answer : C
50. 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
Downlaod Heat & Mass Transfer MCQ PDF

Sharing is caring

Related Post