Heat Transfer - Interview Questions | Exam2Win

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51. 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

E. none of the above.

Explanation:

52. The thermal diffusivities for gases are generally

A. more than those for liquids

B. less than those for liquids

C. more than those for solids

D. dependent on the viscosity

E. same as for the liquids.

Explanation:

53. 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

E. none of the above.

Explanation:

54. According of Kirchhoff law,

A. radiant heat is proportional to fourth power of absolute temperature

B. emissive power depends on temperature

C. emissive power and absorptivity are constant for all bodies

D. ratio of emissive power to absorptive power is maximum for perfectly black body

E. ratio of emissive power to absorptive power for all bodies is same and is equal to the emissive power of a perfectly black body.

Explanation:

55. Joule sec is the unit of

A. universal gas constant

B. kinematic viscosity

C. thermal conductivity

D. Planck's constant

E. none of the above.

Explanation:

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