Refrigeration & Air-Conditioning Practice Set-4

June 7, 2021

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Page 1 of 5

1. The thermostatic expansion valve is used in ________ type of evaporators.

None of these

DX coil

Flooded

Dry

2. The Freon group of refrigerants are

Hydrocarbon refrigerants

Inorganic refrigerants

Zoetrope refrigerants

Halocarbon refrigerants

3. Superheating in a refrigeration cycle

Other factors decide C.O.P

Decreases C.O.P

C.O.P remains unaltered

Increases C.O.P

4. For better C.O.P of refrigerator, the pressure range corresponding to temperature in evaporator and condenser must be

High

Small

Equal

Anything

5. In refrigerator, liquid receiver is required between condenser and flow controlling device, if quantity of refrigerant for system is

There is no such consideration

More than 10 kg

Less than 2 kg

More than or equal to 3.65 kg

6. The conditioned air supplied to the room must have the capacity to take up

None of the above

Room sensible heat load only

Both room sensible heat and latent heat loads

Room latent heat load only

7. Moisture in Freon refrigeration system causes

Ineffective refrigeration

Corrosion of whole system

Freezing automatic regulating valve

High power consumption

8. During sensible cooling,

Partial pressure of vapour remains constant

Relative humidity remains constant

Specific humidity increases

Wet bulb temperature increases

9. In vapour compression refrigeration system, refrigerant occurs as liquid between

Compressor and evaporator

Expansion valve and evaporator

Compressor and condenser

Condenser and expansion valve

10. A heat pump working on a reversed Carnot cycle has a C.O.P. of 5. It works as a refrigerator taking 1 kW of work input. The refrigerating effect will be

2 kW

4 kW

3 kW

1 kW

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11. The sensible heat factor during the heating and humidification process is given by (where h₁ = Enthalpy of air entering the heating coil, h₂ = Enthalpy of air leaving the heating coil, and h_A = Enthalpy of air at the end of humidification process)

(hA - h1)/ (h2 - h1)

(hA - h2)/ (h1 - h2)

(h2 - hA)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

12. The boiling point of ________ is 10.5°C.

R-12

Carbon dioxide

Sulphur dioxide

Ammonia

13. The specific humidity during heating and humidification process.

Decreases

Increases

None of these

Remains constant

14. The relative coefficient of performance is

Actual COP × theoretical COP

Actual COP/theoretical COP

None of these

Theoretical COP/actual COP

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

Which lies between the wet bulb and dew point temperatures of the incoming stream

Which lies between the dry bulb and wet bulb temperatures of the incoming stream

Of adiabatic saturation of incoming stream

Which is lower than the dew point temperature of the incoming stream

16. The superheating in a refrigeration cycle

Does not alter C.O.P.

Increases C.O.P.

Decreases C.O.P.

None of these

17. Refrigeration in aeroplanes usually employs the following refrigerant

Air

Freon-11

Freon-22

CO2

18. The alignment circle is marked on the psychrometric chart at

20°C DBT and 60% RH

26°C DBT and 50% RH

26°C DBT and 60% RH

20°C DBT and 50% RH

19. Ammonia absorption refrigeration cycle requires

Nearly same work input as for vapour compression cycle

Maximum work input

Zero work input

Very little work input

20. During cooling and dehumidification, dry bulb temperature

Increases

None of these

Decreases

Remains constant

Page 3 of 5

21. Which of the following statement is correct?

The constant enthalpy lines are also constant wet bulb temperature lines

All of these

The wet bulb temperature is a measure of enthalpy of moist air

The wet bulb and dry bulb temperature are equal at saturation condition

22. The lower horizontal line of the refrigeration cycle plotted on pressure-enthalpy diagram represents

Evaporation of the refrigerant liquid

Condensation of the refrigerant vapour

Compression of the refrigerant vapour

Metering of the refrigerant liquid

23. Vapour compression refrigeration is somewhat like

Rankine’s cycle

None of the above

Reversed Carnot cycle

Carnot cycle

24. Aqua ammonia is used as refrigerant in the following type of refrigeration system

Absorption

Compression

Direct

Indirect

25. The sub-cooling in a refrigeration cycle

Decreases C.O.P.

Does not alter C.O.P.

None of these

Increases C.O.P.

26. The leakage in a refrigeration system using Freon is detected by

Soap and water

Sulphur sticks

All of these

Halide torch

27. The specific humidity during dehumidification process

Remains constant

None of these

Decreases

Increases

28. The wet bulb depression indicates _________ humidity of the air.

Absolute

Specific

Relative

None of these

29. In vapour compression cycle, the condition of refrigerant is very wet vapour

After passing through the expansion or throttle valve

Before entering the compressor

After passing through the condenser

Before passing through the condenser

30. A standard ice point temperature corresponds to the temperature of

Ice at 4°C

Water at 0°C

Solid and dry ice

Mixture of ice and water under equilibrium conditions

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31. Air refrigeration operates on

Carnot cycle

Brayton cycle

Rankine’s cycle

Reversed Carnot cycle

32. The advantage of dry compression is that

All of the above

It results in high volumetric and mechanical efficiency

It permits higher speeds to be used

It permits complete evaporation in the evaporator

33. A refrigeration cycle operates between condenser temperature of + 27°C and evaporator temperature of -23°C. The Carnot coefficient of performance of cycle will be

1.2

0.2

34. Which of the following refrigerants has lowest freezing point?

CO2

Freon-22

NH3

Freon-12

35. The index which correlates the combined effects of air temperature, relative humidity and air velocity on the human body, is known as

Mean radiant temperature

Dew point temperature

Effective temperature

None of these

36. The wet bulb temperature at 100% relative humidity is ________ dew point temperature.

None of these

Same as

Lower than

Higher than

37. The condensing pressure due to the presence of non-condensable gases, as compared to that actually required for condensing temperatures without non-condensable gases,

Will remain unaffected

Will be lower

Will be higher

May be higher or lower depending upon the nature of non-condensable gases

38. Which of the following refrigerant has the highest freezing point.

Ammonia

R-12

Carbon dioxide

Sulphur dioxide

39. Relative humidity is given by (where p_v = Partial pressure of water vapour, p_b = Barometric pressure, p_s = Pressure of saturated air, p_d = Pressure at dry bulb temperature, p_w = Saturation pressure corresponding to wet bulb temperature, and μ = Degree of saturation)

0.622 Pv / (Pb - Pv)

[Pv (Pb - Pd)]/ [Pd (Pb - Pv)]

μ/[1 - (1 - μ) (Ps/Pb)]

None of these

40. The C.O.P. of a refrigeration cycle with lowering of condenser temperature, keeping the evaporator temperature constant, will

Decrease

May increase or decrease depending on the type of refrigerant used

Increase

Remain unaffected

Page 5 of 5

41. Air conditioning means

Cooling

Dehumidifying

All of these

Heating

42. The condition of refrigerant as it leaves the compressor in a vapour compression system is

Superheated vapour

Wet vapour

Dry saturated vapour

Saturated liquid

43. The bypass factor (B. P. F.) in case of sensible heating of air is (Where t_d₁ = Dry bulb temperature of air entering the heating coil, t_d₂ = Dry bulb temperature of air leaving the heating coil, and t_d₃ = Dry bulb temperature of heating coil)

(td₃ - td₂)/(td₃ - td₁)

(td₃ - td₁)/(td₃ - td₂)

(td₂ - td₃)/(td₃ - td₁)

(td₃ - td₁)/(td₂ - td₃)

44. The coefficient of performance is the ratio of the refrigerant effect to the

Enthalpy increase in compressor

All of the above

Heat of compression

Work done by compressor

45. The refrigeration effect in a dry evaporator compared to flooded evaporator in a similar plant is

More or less depending on ambient conditions

Same

Less

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Refrigeration & Air-Conditioning Practice Set-4

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