Heat and Mass Transfer MCQ Objective Question and Answers Part 2

Heat and Mass Transfer Multiple Choice Objective Questions For Aptitude Interview test useful to Mechanical Students .

HMT MCQ Objective : Part 1 | Part 2 | Part 3

31. Thermal conductivity of glass-wool varies from sample to sample because of variation in

(a) composition
(b) density
(c) porosity
(d) structure
(e) all of the above.
Ans: e

32. 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 are 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
(e) none of the above.
Ans: d

33. Which of the following has maximum value of thermal conductivity
(a) aluminium
(b) steel
(c) brass
(d) copper
(e) lead.
Ans: a

34. Moisture would find its way into insulation by vapour pressure unless it is prevented by
(a) high thickness of insulation
(b) high vapour pressure
(c) less thermal conductivity insulator
(d) a vapour seal
(e) all of the above.
Ans: d

35. Heat is transferred by all three modes of transfer, viz, conduction, convection and radiation in
(a) electric heater
(b) steam condenser
(c) melting of ice
(d) refrigerator condenser coils
(e) boiler.
Ans: e

36. According to 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
(e) rate of heat transfer depends on thermal conductivity and temperature difference.
Ans: c

37. The ratio of heat flow Q1/Q2 from two walls of same thickness having their thermal conductivities as ATj – 2K2 will be
(a) 1
(b) 0.5
(c) 2
(d) 0.25
(e) 4.0
Ans: c

38. 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
(e) none of the above.
Ans: d

39. Thermal diffusivity is
(a) a dimensionless parameter
(b) function of temperature
(c) used as mathematical model
(d) a physical property of the material
(e) useful in case of heat transfer by radiation.
Ans: d

40. Thermal diffusivity of a substance is .
(a) proportional of thermal conductivity
(b) inversely proportional to k
(c) proportional to (k)
(d) inversely proportional to k2
(e) none of the above.
Ans: a

41. Unit of thermal diffusivity is
(a) m2/hr
(b) m2/hr°C
(c) kcal/m2 hr
(d) kcal/m.hr°C
(e) kcal/m2 hr°C.
Ans: a

43. Thermal conductivity of wood depends on
(a) moisture
(b) density
(c) temperature
(d) all of the above
(e) none of the above.
Ans: d

44. 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
(e) none of the above.
Ans: c

45. Film coefficient is defined as Inside diameter of tube
(a) Equivalent thickness of film
(b) Thermal conductivity Equivalent thickness of film Specific heat x Viscocity
(c) Thermal conductivity Molecular diffusivity of momentum Thermal diffusivity
(d) Film coefficient x Inside diameter Thermal conductivity
(e) none of the above.
Ans: b

46. Heat conducted through 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
(e) heat-transfer.
Ans: d

49. 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
(e) absorptivity.
Ans: d

50. 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
(e) none of the above.
Ans: b

51. 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
(e) none of the above.
Ans: c

53. 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
(e) 1 : 4.
Ans: c

55. A non-dimensional number generally associated with natural convection heat transfer is
(a) Grashoff number
(b) Nusselt number
(c) Weber number
(d) Prandtl number
(e) Reynold number.
Ans: a

56. 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
(e) depends on temperature conditions.
Ans: a

57. 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
(e) none of the above.
Ans: d

58. In counter flow heat exchanges
(a) both the fluids at inlet (of heat ex¬changer where hot fluid enters) are in their coldest state
(b) both the fluids at inlet are in their hot¬test 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
(e) any combination is possible depending on design of heat exchanger.
Ans: b

59. 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
(e) unpredictable.
Ans: a

61. 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
(e) irregular surfaces.
Ans: a