Refrigeration & Air-Conditioning Practice Set-1

May 16, 2021

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1. The reduced ambient air cooling system has

One cooling turbine and one heat exchanger

Two cooling turbines and one heat exchanger

Two cooling turbines and two heat exchangers

One cooling turbine and two heat exchangers

2. 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

Relative humidity

Absolute humidity

Humidity ratio

Degree of saturation

3. Under cooling in a refrigeration cycle

Other factors decide C.O.P

C.O.P remains unaltered

Decreases C.O.P

Increases C.O.P

4. During humidification process, dry bulb temperature

None of these

Increases

Decreases

Remains constant

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

Capillary tube

Manually operated valve

Electrically operated throttling valve

Thermostatic valve

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

CO₂

Ammonia

All of these

R-12

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

Increase

Remain unaffected

May increase or decrease depending on the type of refrigerant used

Decrease

8. The refrigerant widely used in domestic refrigerators is

Ammonia

Carbon dioxide

R-12

Sulphur dioxide

9. During humidification process, __________ increases.

Wet bulb temperature

Specific humidity

Dry bulb temperature

Relative humidity

10. Chaperon equation is a relation between

Temperature, pressure and enthalpy

Temperature, pressure, specific volume and enthalpy

Specific volume and enthalpy

Temperature and enthalpy

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

Depends on other factors

Remain same

Decreases

Increases

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

Before passing through the condenser

After passing through the condenser

After passing through the expansion throttle valve

Before entering the expansion valve

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

Condenser

Compressor

Expansion valve

Evaporator

14. During sensible cooling of air ________ decreases.

Dry bulb temperature

Wet bulb temperature

Relative humidity

Specific humidity

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

Lower

None of these

Same

Higher

16. One ton refrigeration corresponds to

80 kcal/ min

50 kcal/ min

80 kcal/ hr

50 kcal/ hr

17. During dehumidification process, the relative humidity

Increases

None of these

Remains constant

Decreases

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

Saturated liquid

Dry saturated vapour

Wet vapour

Superheated vapour

19. Absorption system normally uses the following refrigerant

Freon-22

CO2

Ammonia

Freon-11

20. An important characteristic of absorption system of refrigeration is

Very little power consumption

Quiet operation

Noisy operation

Cooling below 0°C

Page 3 of 4

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

Large displacements and high condensing pressures

Small displacements and low condensing pressures

Large displacements and low condensing pressures

Small displacements and high condensing pressures

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

Expansion valve

Evaporator

Compressor

Condenser

23. The fluids used in Electrolux refrigerator are

None of these

Ammonia and hydrogen

Ammonia, water and hydrogen

Water and hydrogen

24. 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

Wet bulb temperature

Dry bulb temperature

Dew point temperature

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

Using reagents

Halide torch which on detection produces greenish flame lighting

Smelling

Sulphur sticks which on detection gives white smoke

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

Zero

1.0

0.75

0.5

27. Which of the following statement is correct?

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

All of these

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

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

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

Bright green

Red

Yellow

Orange

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

Zero

100

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

Low pressure side near receiver

High pressure side close to receiver

Delivery of compressor

Suction of compressor

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31. Which of the following statement is wrong?

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

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

32. The moisture in a refrigerant is removed by

Driers

Safety relief valve

Dehumidifier

Evaporator

33. The vapour pressure of refrigerant should be

Could be anything

Higher than atmospheric pressure

Lower than atmospheric pressure

Equal to atmospheric pressure

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

Less

More/less depending on size of plant

Same

35. 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

Bigger cabinet should be used

Perfectly tight vapour seal should be used

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

56 bars

24 bars

Atmospheric pressure

Slightly above atmospheric pressure

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

Cooling and dehumidification

Dehumidification

Humidification

Heating and humidification

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

Wet vapour

Dry vapour

High pressure saturated liquid

Very wet vapour

39. Pick up the incorrect statement

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

Lithium bromide used in vapour absorption cycle is non volatile

Lithium bromide plant can't operate below 0°C

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

40. During sensible heating of air _________ decreases.

Relative humidity

Dry bulb temperature

Wet bulb temperature

Specific humidity

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