Heat Transfer - Interview Questions | Exam2Win

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36. 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

E. none of the above.

Explanation:

37. 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.

Explanation:

38. 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.

Explanation:

39. 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.

Explanation:

40. In heat transfer, conductance equals conductivity (kcal/hr/sqm/�C/cm) divided by

A. hr (time)

B. sqm (area)

C. �C (temperature)

D. cm (thickness)

E. kcal (heat).

Explanation:

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