Refrigeration And Air Conditioning MCQ Questions & Answers

1

Nusselt number (N_N) is given by

A) $${{\text{N}}_{\text{N}}} = \frac{{{\text{h}}l}}{{\text{k}}}$$ B) $${{\text{N}}_{\text{N}}} = \frac{{\mu {{\text{c}}_{\text{p}}}}}{{\text{k}}}$$ C) $${{\text{N}}_{\text{N}}} = \frac{{\rho {\text{V}}l}}{\mu }$$ D) $${{\text{N}}_{\text{N}}} = \frac{{{{\text{V}}^2}}}{{{\text{t}}{{\text{c}}_{\text{p}}}}}$$

Discuss

Answer & Solution

Answer: Option A

Solution:

Nusselt number (N_N) is the ratio of convective to conductive heat transfer at a boundary in a fluid.
A Nusselt number of value one represents heat transfer by pure conduction.
Nusselt number (N_N) is given by $${{\text{N}}_{\text{N}}} = \frac{{{\text{h}}l}}{{\text{k}}}$$

2

In case of sensible heating of air, the coil efficiency is given by (where B.P.F. = Bypass factor)

A) B.P.F. - 1 B) 1 - B.P.F. C) $$\frac{1}{{{\text{B}}{\text{.P}}{\text{.F}}{\text{.}}}}$$ D) 1 + B.P.F.

Discuss

Answer & Solution

Answer: Option B

Solution:

In case of sensible heating of air, the coil efficiency is given by 1 - B.P.F.

3

The undesirable property of a refrigerant is

A) Non-toxic B) Non-flammable C) Non-explosive D) High boiling point

Discuss

Answer & Solution

Answer: Option D

Solution:

It is very important that the refrigerant has a low boiling point, that is it should have the ability to turn into gas easily when it absorbs heat.
If it has a high boiling point, the compressor will have to create too much of a vacuum in order to lower the pressure to make vaporization happen.

4

The desirable property of a refrigerant is

A) Low boiling point B) High critical temperature C) High latent heat of vaporisation D) All of these

Discuss

Answer & Solution

Answer: Option D

Solution:

Physical Properties of Refrigerants
- Low Condensing Pressure
- High Evaporator Pressure
- High Critical Pressure
- High Vapor Density
- High Dielectric strength
- High Latent Heat of Vaporization
- High Heat Transfer Coefficient

5

The operating pressure for refrigerating units using R-12 as a refrigerant is

A) 2 bar B) 8 bar C) 15 bar D) 30 bar

Discuss

Answer & Solution

Answer: Option B

Solution:

The operating pressure for refrigerating units using R-12 as a refrigerant is 8 bar

6

Cooling water is required for following equipment in ammonia absorption plant

A) Condenser B) Evaporator C) Absorber D) Condenser, absorber and separator (rectifier)

Discuss

Answer & Solution

Answer: Option D

Solution:

Cooling water is required for Condenser, absorber and separator (rectifier) in ammonia absorption plant

7

The coefficient of performance of a domestic refrigerator is ________ as compared to a domestic air-conditioner.

A) Same B) Less C) More D) None of these

Discuss

Answer & Solution

Answer: Option B

Solution:

The coefficient of performance of a domestic refrigerator is less as compared to a domestic air-conditioner.

8

In aqua ammonia and Lithium bromide water absorption refrigeration systems, the refrigerants are respectively

A) Water and water B) Water and lithium bromide C) Ammonia and lithium bromide D) Ammonia and water

Discuss

Answer & Solution

Answer: Option D

Solution:

In aqua ammonia and Lithium bromide water absorption refrigeration systems, the refrigerants are respectively Ammonia and water

9

In order to cool and dehumidify a stream of moist air, it must be passed over the coil at a temperature

A) Which lies between the dry bulb and wet bulb temperatures of the incoming stream B) Which lies between the wet bulb and dew point temperatures of the incoming stream C) Which is lower than the dew point temperature of the incoming stream D) Of adiabatic saturation of incoming stream

Discuss

Answer & Solution

Answer: Option C

Solution:

In order to cool and dehumidify a stream of moist air, it must be passed over the coil at a temperature Which is lower than the dew point temperature of the incoming stream

10

During heating and dehumidification process, dry bulb temperature

A) Remains constant B) Increases C) Decreases D) None of these

Discuss

Answer & Solution

Answer: Option B

Solution:

During the heating and dehumidification process dry bulb temperature of the air increases while its dew point and wet bulb temperature reduces.

Refrigeration And Air Conditioning MCQ Questions & Answers | Mechanical Engineering