Refrigeration & Air-Conditioning Practice Set-4

June 7, 2021

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Page 1 of 5

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

Ammonia

Carbon dioxide

R-12

Sulphur dioxide

2. Moisture in Freon refrigeration system causes

Freezing automatic regulating valve

Ineffective refrigeration

High power consumption

Corrosion of whole system

3. Vapour compression refrigeration is somewhat like

Reversed Carnot cycle

Carnot cycle

Rankine’s cycle

None of the above

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

Condensation of the refrigerant vapour

Compression of the refrigerant vapour

Metering of the refrigerant liquid

Evaporation of the refrigerant liquid

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

Of adiabatic saturation of incoming stream

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

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

Room latent heat load only

Room sensible heat load only

None of the above

Both room sensible heat and latent heat loads

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

Less

More or less depending on ambient conditions

Same

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

None of these

Lower than

Same as

Higher than

9. 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)

μ/[1 - (1 - μ) (Ps/Pb)]

0.622 Pv / (Pb - Pv)

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

None of these

10. The specific humidity during heating and humidification process.

Increases

Decreases

None of these

Remains constant

Page 2 of 5

11. 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

12. 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

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

Relative

Absolute

None of these

Specific

14. Superheating in a refrigeration cycle

C.O.P remains unaltered

Other factors decide C.O.P

Decreases C.O.P

Increases C.O.P

15. Ammonia absorption refrigeration cycle requires

Zero work input

Nearly same work input as for vapour compression cycle

Maximum work input

Very little work input

16. 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

Mean radiant temperature

Dew point temperature

17. The Freon group of refrigerants are

Halocarbon refrigerants

Zoetrope refrigerants

Hydrocarbon refrigerants

Inorganic refrigerants

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

NH3

CO2

Freon-12

Freon-22

19. Air refrigeration operates on

Reversed Carnot cycle

Brayton cycle

Rankine’s cycle

Carnot cycle

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

After passing through the expansion or throttle valve

Before passing through the condenser

Before entering the compressor

After passing through the condenser

Page 3 of 5

21. 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

Remain unaffected

Decrease

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

Sulphur sticks

Soap and water

All of these

Halide torch

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

Condenser and expansion valve

Expansion valve and evaporator

Compressor and condenser

Compressor and evaporator

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

R-12

Carbon dioxide

Sulphur dioxide

Ammonia

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

Direct

Compression

Absorption

Indirect

26. The relative coefficient of performance is

Actual COP × theoretical COP

None of these

Actual COP/theoretical COP

Theoretical COP/actual COP

27. The superheating in a refrigeration cycle

Does not alter C.O.P.

Decreases C.O.P.

Increases C.O.P.

None of these

28. 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)

(td₂ - td₃)/(td₃ - td₁)

(td₃ - td₁)/(td₂ - td₃)

(td₃ - td₁)/(td₃ - td₂)

(td₃ - td₂)/(td₃ - td₁)

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

Ice at 4°C

Water at 0°C

Mixture of ice and water under equilibrium conditions

Solid and dry ice

30. During sensible cooling,

Partial pressure of vapour remains constant

Relative humidity remains constant

Wet bulb temperature increases

Specific humidity increases

Page 4 of 5

31. During cooling and dehumidification, dry bulb temperature

Remains constant

Increases

None of these

Decreases

32. 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

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

Anything

Small

High

Equal

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

26°C DBT and 60% RH

20°C DBT and 60% RH

20°C DBT and 50% RH

26°C DBT and 50% RH

35. The sub-cooling in a refrigeration cycle

Decreases C.O.P.

Does not alter C.O.P.

None of these

Increases C.O.P.

36. Which of the following statement is correct?

The constant enthalpy lines are also constant wet bulb temperature lines

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

All of these

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

37. The specific humidity during dehumidification process

Decreases

None of these

Remains constant

Increases

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

None of these

Dry

DX coil

Flooded

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

Heat of compression

Work done by compressor

Enthalpy increase in compressor

All of the above

40. 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

Page 5 of 5

41. Air conditioning means

Dehumidifying

Heating

Cooling

All of these

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

Dry saturated vapour

Superheated vapour

Wet vapour

Saturated liquid

43. Refrigeration in aeroplanes usually employs the following refrigerant

Freon-11

Freon-22

Air

CO2

44. 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

2 kW

3 kW

1 kW

45. 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)

(h2 - hA)/ (h1 - h2)

(hA - h2)/ (h1 - h2)

(hA - h1)/ (h2 - h1)

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Refrigeration & Air-Conditioning Practice Set-4

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