Refrigeration & Air-Conditioning Practice Set-4

June 7, 2021

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Page 1 of 5

1. Air refrigeration operates on

Rankine’s cycle

Carnot cycle

Reversed Carnot cycle

Brayton cycle

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

Compressor and condenser

Expansion valve and evaporator

Condenser and expansion valve

Compressor and evaporator

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

There is no such consideration

Less than 2 kg

More than 10 kg

More than or equal to 3.65 kg

4. 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

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

Evaporation of the refrigerant liquid

Metering of the refrigerant liquid

Condensation of the refrigerant vapour

Compression of the refrigerant vapour

6. The advantage of dry compression is that

It results in high volumetric and mechanical efficiency

It permits complete evaporation in the evaporator

It permits higher speeds to be used

All of the above

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

R-12

Sulphur dioxide

Ammonia

Carbon dioxide

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

Less

Same

More or less depending on ambient conditions

9. 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

Effective temperature

None of these

Dew point temperature

10. 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)

(td₃ - td₂)/(td₃ - td₁)

(td₂ - td₃)/(td₃ - td₁)

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11. Ammonia absorption refrigeration cycle requires

Zero work input

Nearly same work input as for vapour compression cycle

Very little work input

Maximum work input

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

Solid and dry ice

Water at 0°C

Ice at 4°C

Mixture of ice and water under equilibrium conditions

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

None of the above

Room latent heat load only

Both room sensible heat and latent heat loads

Room sensible heat load only

14. 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)

None of these

μ/[1 - (1 - μ) (Ps/Pb)]

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

0.622 Pv / (Pb - Pv)

15. Moisture in Freon refrigeration system causes

High power consumption

Ineffective refrigeration

Freezing automatic regulating valve

Corrosion of whole system

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

Increase

Decrease

Remain unaffected

May increase or decrease depending on the type of refrigerant used

17. 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

4 kW

3 kW

2 kW

1 kW

18. During sensible cooling,

Relative humidity remains constant

Wet bulb temperature increases

Partial pressure of vapour remains constant

Specific humidity increases

19. 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 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

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

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

Before passing through the condenser

After passing through the condenser

After passing through the expansion or throttle valve

Before entering the compressor

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21. The relative coefficient of performance is

Theoretical COP/actual COP

Actual COP/theoretical COP

Actual COP × theoretical COP

None of these

22. Refrigeration in aeroplanes usually employs the following refrigerant

Air

CO2

Freon-11

Freon-22

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

Lower than

Same as

None of these

Higher than

24. 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

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

Freon-22

NH3

CO2

Freon-12

26. The superheating in a refrigeration cycle

None of these

Does not alter C.O.P.

Decreases C.O.P.

Increases C.O.P.

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

Relative

Specific

Absolute

None of these

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

High

Equal

Anything

Small

29. 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)

(h1 - h2)/ (hA - h2)

(h2 - hA)/ (h1 - h2)

(hA - h2)/ (h1 - h2)

30. 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 lower

Will be higher

Will remain unaffected

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

Page 4 of 5

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

Ammonia

Sulphur dioxide

Carbon dioxide

R-12

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

None of these

Flooded

DX coil

Dry

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

Wet vapour

Saturated liquid

Dry saturated vapour

Superheated vapour

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

26°C DBT and 60% RH

20°C DBT and 50% RH

20°C DBT and 60% RH

26°C DBT and 50% RH

35. The sub-cooling in a refrigeration cycle

Increases C.O.P.

Does not alter C.O.P.

None of these

Decreases C.O.P.

36. During cooling and dehumidification, dry bulb temperature

Decreases

Remains constant

None of these

Increases

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

All of these

Halide torch

Sulphur sticks

Soap and water

38. Superheating in a refrigeration cycle

Decreases C.O.P

Other factors decide C.O.P

C.O.P remains unaltered

Increases C.O.P

39. Which of the following statement is correct?

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

The constant enthalpy lines are also constant wet bulb temperature lines

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

Indirect

Absorption

Compression

Direct

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41. The Freon group of refrigerants are

Inorganic refrigerants

Hydrocarbon refrigerants

Halocarbon refrigerants

Zoetrope refrigerants

42. The specific humidity during heating and humidification process.

Decreases

None of these

Remains constant

Increases

43. Air conditioning means

Heating

All of these

Cooling

Dehumidifying

44. Vapour compression refrigeration is somewhat like

None of the above

Rankine’s cycle

Reversed Carnot cycle

Carnot cycle

45. The specific humidity during dehumidification process

Increases

Decreases

Remains constant

None of these

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Refrigeration & Air-Conditioning Practice Set-4

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