Refrigeration & Air-Conditioning Practice Set-1

May 16, 2021

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1. The condition of refrigerant after passing through the expansion or throttle valve, in a vapour compression system is

High pressure saturated liquid

Dry vapour

Wet vapour

Very wet vapour

2. Under cooling in a refrigeration cycle

Other factors decide C.O.P

Increases C.O.P

C.O.P remains unaltered

Decreases C.O.P

3. The temperature of air recorded by a thermometer, when it is not affected by the moisture present in the air, is called

None of these

Dry bulb temperature

Dew point temperature

Wet bulb temperature

4. The COP of a vapour compression plant in comparison to vapour absorption plant is

More/less depending on size of plant

Less

Same

5. For proper refrigeration in a cabinet, if the temperature and vapour pressure difference between cabinet and atmosphere is high, then

Refrigerant with lower evaporation temperature should be used

Smaller cabinet should be used

Perfectly tight vapour seal should be used

Bigger cabinet should be used

6. Where does the lowest temperature occur in a vapour compression cycle?

Condenser

Compressor

Evaporator

Expansion valve

7. Absorption system normally uses the following refrigerant

Freon-22

Freon-11

Ammonia

CO2

8. In a refrigeration cycle, the flow of refrigerant is controlled by

Expansion valve

Compressor

Evaporator

Condenser

9. During humidification process, dry bulb temperature

Remains constant

None of these

Increases

Decreases

10. The leaks in a refrigeration system using Freon are detected by

Smelling

Sulphur sticks which on detection gives white smoke

Halide torch which on detection produces greenish flame lighting

Using reagents

Page 2 of 4

11. During sensible cooling of air ________ decreases.

Specific humidity

Dry bulb temperature

Relative humidity

Wet bulb temperature

12. One ton refrigeration corresponds to

80 kcal/ hr

50 kcal/ min

80 kcal/ min

50 kcal/ hr

13. The moisture in a refrigerant is removed by

Dehumidifier

Driers

Safety relief valve

Evaporator

14. Which of the following statement is correct?

Sub-cooling can be achieved by circulating more quantity of cooling water through the condenser.

All of these

In vapour absorption refrigerator, the compression of refrigerant is avoided.

In vapour compression refrigeration, the vapour is drawn in the compressor cylinder during its suction stroke and is compressed adiabatically during the compression stroke.

15. Allowable pressure on high pressure side or ammonia absorption system is of the order of

24 bars

Slightly above atmospheric pressure

56 bars

Atmospheric pressure

16. The refrigerant widely used in domestic refrigerators is

Ammonia

R-12

Carbon dioxide

Sulphur dioxide

17. In vapour compression cycle using NH₃ as refrigerant, initial charge is filled at

Suction of compressor

High pressure side close to receiver

Delivery of compressor

Low pressure side near receiver

18. The wet bulb depression is zero when relative humidity is

Zero

1.0

0.5

0.75

19. The fluids used in Electrolux refrigerator are

Water and hydrogen

None of these

Ammonia and hydrogen

Ammonia, water and hydrogen

20. At lower temperatures and pressures, the latent heat of vaporisation of a refrigerant

Remain same

Increases

Depends on other factors

Decreases

Page 3 of 4

21. In vapour compression cycle, the condition of refrigerant is saturated liquid

Before entering the expansion valve

After passing through the condenser

After passing through the expansion throttle valve

Before passing through the condenser

22. The centrifugal compressors are generally used for refrigerants that require

Large displacements and low condensing pressures

Large displacements and high condensing pressures

Small displacements and high condensing pressures

Small displacements and low condensing pressures

23. The colour of the flame of halide torch, in case of leakage of Freon refrigerant, will change to

Orange

Yellow

Bright green

Red

24. An important characteristic of absorption system of refrigeration is

Noisy operation

Cooling below 0°C

Quiet operation

Very little power consumption

25. During sensible heating of air _________ decreases.

Specific humidity

Relative humidity

Dry bulb temperature

Wet bulb temperature

26. Chaperon equation is a relation between

Temperature and enthalpy

Temperature, pressure and enthalpy

Temperature, pressure, specific volume and enthalpy

Specific volume and enthalpy

27. During humidification process, __________ increases.

Relative humidity

Dry bulb temperature

Specific humidity

Wet bulb temperature

28. During dehumidification process, the relative humidity

Decreases

None of these

Remains constant

Increases

29. In a domestic vapour compression refrigerator, the refrigerant commonly used is

CO₂

R-12

Ammonia

All of these

30. The C.O.P of a refrigeration cycle with increase in evaporator temperature, keeping condenser temperature constant, will

Increase

May increase or decrease depending on the type of refrigerant used

Decrease

Remain unaffected

Page 4 of 4

31. The C.O.P. of a Carnot refrigerator in winter will be _________ as compared to C.O.P. in summer.

Lower

Higher

None of these

Same

32. Pick up the incorrect statement

Lithium bromide used in vapour absorption cycle is non volatile

A separator is used in lithium bromide plant to remove the unwanted water vapour by condensing

Lithium bromide plant can't operate below 0°C

Concentration of solution coming out of lithium bromide generator is more in comparison to that entering the generator

33. The process, generally used in winter air-conditioning to warm and humidity the air, is called

Cooling and dehumidification

Dehumidification

Heating and humidification

Humidification

34. The reduced ambient air cooling system has

One cooling turbine and two heat exchangers

Two cooling turbines and one heat exchanger

Two cooling turbines and two heat exchangers

One cooling turbine and one heat exchanger

35. Domestic refrigerator working on vapour compression cycle uses the following type of expansion device

Manually operated valve

Electrically operated throttling valve

Thermostatic valve

Capillary tube

36. The ratio of actual mass of water vapour in a given volume of moist air to the mass of water vapour in the same volume of saturated air at the same temperature and pressure, is called

Degree of saturation

Relative humidity

Absolute humidity

Humidity ratio

37. The vapour pressure of refrigerant should be

Higher than atmospheric pressure

Could be anything

Lower than atmospheric pressure

Equal to atmospheric pressure

38. Which of the following statement is wrong?

The effect of under-cooling the liquid refrigerant is to decrease the coefficient of performance.

In vapour compression cycle, the useful part of the heat transfer is at the condenser.

In ammonia-hydrogen (Electrolux) refrigerator, no compressor, pump or fan is required.

The performance of the vapour compression refrigerator varies considerably with both vaporising and condensing temperatures.

39. For air conditioning the operation theater in a hospital, the percentage of outside air in the air supplied is

Zero

100

40. In a vapour compression system, the condition of refrigerant before passing through the condenser is

Dry saturated vapour

Wet vapour

Superheated vapour

Saturated liquid

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