Refrigeration & Air-Conditioning Practice Set-4

June 7, 2021

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Page 1 of 5

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

Lower than

Higher than

None of these

Same as

2. Ammonia absorption refrigeration cycle requires

Maximum work input

Nearly same work input as for vapour compression cycle

Zero work input

Very little work input

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

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

Will be higher

Will be lower

Will remain unaffected

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

Increase

May increase or decrease depending on the type of refrigerant used

Decrease

Remain unaffected

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

Compressor and condenser

Compressor and evaporator

Expansion valve and evaporator

Condenser and expansion valve

6. 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

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

Before entering the compressor

Before passing through the condenser

After passing through the expansion or throttle valve

After passing through the condenser

8. The advantage of dry compression is that

It results in high volumetric and mechanical efficiency

All of the above

It permits higher speeds to be used

It permits complete evaporation in the evaporator

9. Refrigeration in aeroplanes usually employs the following refrigerant

Freon-11

Air

CO2

Freon-22

10. Moisture in Freon refrigeration system causes

Ineffective refrigeration

Freezing automatic regulating valve

High power consumption

Corrosion of whole system

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

DX coil

Flooded

None of these

Dry

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

Compression

Absorption

Direct

Indirect

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

CO2

NH3

Freon-22

Freon-12

14. The sub-cooling in a refrigeration cycle

None of these

Decreases C.O.P.

Increases C.O.P.

Does not alter C.O.P.

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

Carbon dioxide

Sulphur dioxide

Ammonia

R-12

16. Air refrigeration operates on

Carnot cycle

Reversed Carnot cycle

Brayton cycle

Rankine’s cycle

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

Saturated liquid

Wet vapour

Dry saturated vapour

Superheated vapour

18. 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)

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

0.622 Pv / (Pb - Pv)

None of these

μ/[1 - (1 - μ) (Ps/Pb)]

19. The Freon group of refrigerants are

Halocarbon refrigerants

Hydrocarbon refrigerants

Zoetrope refrigerants

Inorganic refrigerants

20. Superheating in a refrigeration cycle

Decreases C.O.P

Other factors decide C.O.P

Increases C.O.P

C.O.P remains unaltered

Page 3 of 5

21. The specific humidity during heating and humidification process.

Decreases

None of these

Increases

Remains constant

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

Carbon dioxide

Ammonia

Sulphur dioxide

R-12

23. The relative coefficient of performance is

None of these

Theoretical COP/actual COP

Actual COP/theoretical COP

Actual COP × theoretical COP

24. 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

3 kW

4 kW

1 kW

25. During sensible cooling,

Partial pressure of vapour remains constant

Wet bulb temperature increases

Specific humidity increases

Relative humidity remains constant

26. 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

More than or equal to 3.65 kg

Less than 2 kg

27. The specific humidity during dehumidification process

Decreases

None of these

Remains constant

Increases

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

Condensation of the refrigerant vapour

Evaporation of the refrigerant liquid

Metering of the refrigerant liquid

Compression of the refrigerant vapour

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

Specific

None of these

Relative

Absolute

30. 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)/(td₂ - td₃)

(td₃ - td₁)/(td₃ - td₂)

(td₃ - td₂)/(td₃ - td₁)

(td₂ - td₃)/(td₃ - td₁)

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31. 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

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

Small

Equal

High

Anything

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

None of the above

Room sensible heat load only

Room latent heat load only

Both room sensible heat and latent heat loads

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

Soap and water

Sulphur sticks

Halide torch

All of these

35. 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 - h2)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

(h2 - hA)/ (h1 - h2)

(hA - h1)/ (h2 - h1)

36. 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 is lower than the dew point temperature of the incoming stream

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

Of adiabatic saturation of incoming stream

37. 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

Dew point temperature

Effective temperature

Mean radiant temperature

38. 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

39. Vapour compression refrigeration is somewhat like

None of the above

Carnot cycle

Rankine’s cycle

Reversed Carnot cycle

40. 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

Page 5 of 5

41. Air conditioning means

Cooling

Dehumidifying

All of these

Heating

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

20°C DBT and 50% RH

20°C DBT and 60% RH

26°C DBT and 50% RH

26°C DBT and 60% RH

43. During cooling and dehumidification, dry bulb temperature

Decreases

Increases

None of these

Remains constant

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

All of the above

Heat of compression

Enthalpy increase in compressor

Work done by compressor

45. The superheating in a refrigeration cycle

Increases C.O.P.

None of these

Does not alter C.O.P.

Decreases C.O.P.

Refrigeration & Air-Conditioning Practice Set-4

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