Heat Transfer, Refrigeration and Air Conditioning – Section 1

1. The wet bulb temperature during sensible heating of the air

A. remains constant
B. increases
C. decreases

Correct Answer: B. increases

2. The C.O.P. of an absorption type refrigerator is given by (where T1 = Temperature at which the working substance receives heat, T2 = Temperature of cooling water, and T3 = Evaporator temperature)

ht-se1-02

Correct Answer: Option B

3. Which of the following statement is wrong?

A. The heat transfer in liquid and gases takes place according to convection.
B. The amount of heat flow through a body is dependent upon the material of the body.
C. The thermal conductivity of solid metals increases with rising in temperature,
D. The logarithmic mean temperature difference is not equal to the arithmetic mean temperature difference.

Correct Answer: C. The thermal conductivity of solid metals increases with rising in temperature,

4. In free convection heat transfer transition from laminar to turbulent flow is governed by the critical value of the

A.Reynold’s number
B.Grashoff’s number
C.Reynold’s number, Grashoff’s number
D.Prandtl number, Grashoff’s number

Correct Answer: D.Prandtl number, Grashoff’s number

5. In a refrigerating machine, heat rejected is __________ heat absorbed.

A. equal to
B. less than
C. greater than

Correct Answer: C. greater than

6. The humidity ratio or specific humidity is the mass of water vapor present in

A. 1 mof wet air
B. 1 mof dry air
C. 1 kg of wet air
D. 1 kg of dry air

Correct Answer: D. 1 kg of dry air

7. The formation of frost on cooling coils in a refrigerator

A. increases heat transfer
B. improves C.O.P. of the system
C. increases power consumption
D. reduces power consumption

Correct Answer: C. increases power consumption

8. The by-pass factor for a cooling coil

A. increases with increase in velocity of air passing through it
B. decreases with increase in velocity of air passing through it
C. remains unchanged with increase in velocity of air passing through it
D. may increase or decrease with increase in velocity of air passing through it depending upon the condition of air entering

Correct Answer: A. increases with increase in velocity of air passing through it

9. The difference between dry bulb temperature and wet bulb temperature is called

A. dry bulb depression
B. wet bulb depression
C. dew point depression
D. degree of saturation

Correct Answer: B. wet bulb depression

10. Defrosting of a refrigerator may be done by stopping the compressor for a short period.

A. Correct
B. Incorrect

Correct Answer: A. Correct

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