Refrigeration & Air-Conditioning Practice Set-4

June 7, 2021

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Page 1 of 5

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

Metering of the refrigerant liquid

Condensation of the refrigerant vapour

Compression of the refrigerant vapour

Evaporation of the refrigerant liquid

2. Ammonia absorption refrigeration cycle requires

Very little work input

Nearly same work input as for vapour compression cycle

Maximum work input

Zero work input

3. The specific humidity during heating and humidification process.

Increases

None of these

Remains constant

Decreases

4. 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

1 kW

2 kW

3 kW

4 kW

5. The superheating in a refrigeration cycle

Decreases C.O.P.

None of these

Does not alter C.O.P.

Increases C.O.P.

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

Direct

Indirect

Absorption

Compression

7. The sub-cooling in a refrigeration cycle

Does not alter C.O.P.

None of these

Decreases C.O.P.

Increases C.O.P.

8. During sensible cooling,

Wet bulb temperature increases

Specific humidity increases

Relative humidity remains constant

Partial pressure of vapour remains constant

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

None of these

Effective temperature

Dew point temperature

Mean radiant temperature

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

Carbon dioxide

Ammonia

R-12

Sulphur dioxide

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

None of these

Relative

Specific

Absolute

12. During cooling and dehumidification, dry bulb temperature

Increases

Remains constant

Decreases

None of these

13. Air refrigeration operates on

Brayton cycle

Carnot cycle

Rankine’s cycle

Reversed Carnot cycle

14. 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)

(h1 - h2)/ (hA - h2)

(hA - h2)/ (h1 - h2)

(h2 - hA)/ (h1 - h2)

(hA - h1)/ (h2 - h1)

15. The Freon group of refrigerants are

Halocarbon refrigerants

Hydrocarbon refrigerants

Inorganic refrigerants

Zoetrope refrigerants

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

Enthalpy increase in compressor

Heat of compression

All of the above

Work done by compressor

17. Which of the following statement is correct?

All of these

The constant enthalpy lines are also constant wet bulb temperature lines

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

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

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

Dry

DX coil

None of these

Flooded

19. The specific humidity during dehumidification process

Decreases

Remains constant

None of these

Increases

20. The advantage of dry compression is that

All of the above

It permits higher speeds to be used

It permits complete evaporation in the evaporator

It results in high volumetric and mechanical efficiency

Page 3 of 5

21. 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

0.2

1.2

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

Same as

None of these

Lower than

Higher than

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

After passing through the condenser

Before passing through the condenser

Before entering the compressor

After passing through the expansion or throttle valve

24. Moisture in Freon refrigeration system causes

High power consumption

Freezing automatic regulating valve

Ineffective refrigeration

Corrosion of whole system

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

26°C DBT and 60% RH

26°C DBT and 50% RH

20°C DBT and 60% RH

20°C DBT and 50% RH

26. Air conditioning means

Dehumidifying

Heating

All of these

Cooling

27. 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)

μ/[1 - (1 - μ) (Ps/Pb)]

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

None of these

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

More than or equal to 3.65 kg

Less than 2 kg

More than 10 kg

There is no such consideration

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

Condenser and expansion valve

Compressor and evaporator

Compressor and condenser

Expansion valve and evaporator

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

Wet vapour

Saturated liquid

Superheated vapour

Dry saturated vapour

Page 4 of 5

31. Vapour compression refrigeration is somewhat like

Carnot cycle

None of the above

Rankine’s cycle

Reversed Carnot cycle

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

May increase or decrease depending on the type of refrigerant used

Increase

Decrease

Remain unaffected

33. Superheating in a refrigeration cycle

Decreases C.O.P

Other factors decide C.O.P

Increases C.O.P

C.O.P remains unaltered

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

Room latent heat load only

Both room sensible heat and latent heat loads

None of the above

Room sensible heat load only

35. 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 - td₁)/(td₃ - td₂)

(td₃ - td₁)/(td₂ - td₃)

(td₂ - td₃)/(td₃ - td₁)

(td₃ - td₂)/(td₃ - td₁)

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

Sulphur dioxide

Carbon dioxide

Ammonia

R-12

37. The relative coefficient of performance is

Theoretical COP/actual COP

Actual COP × theoretical COP

Actual COP/theoretical COP

None of these

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

Small

Equal

Anything

High

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

Mixture of ice and water under equilibrium conditions

Water at 0°C

Ice at 4°C

Solid and dry ice

40. 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

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

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

Of adiabatic saturation of incoming stream

Page 5 of 5

41. 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 be higher

Will remain unaffected

Will be lower

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

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

All of these

Sulphur sticks

Halide torch

Soap and water

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

Same

More or less depending on ambient conditions

Less

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

NH3

CO2

Freon-12

Freon-22

45. Refrigeration in aeroplanes usually employs the following refrigerant

Freon-22

CO2

Air

Freon-11

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Refrigeration & Air-Conditioning Practice Set-4

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