Refrigeration & Air-Conditioning Practice Set-4

June 7, 2021

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Page 1 of 5

1. The specific humidity during heating and humidification process.

Remains constant

Increases

None of these

Decreases

2. Vapour compression refrigeration is somewhat like

None of the above

Carnot cycle

Rankine’s cycle

Reversed Carnot cycle

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

Direct

Compression

Absorption

Indirect

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

Ice at 4°C

Mixture of ice and water under equilibrium conditions

Water at 0°C

Solid and dry ice

5. Which of the following statement is correct?

All of these

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

The constant enthalpy lines are also constant wet bulb temperature lines

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

6. 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

7. 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

8. Ammonia absorption refrigeration cycle requires

Maximum work input

Zero work input

Nearly same work input as for vapour compression cycle

Very little work input

9. Air refrigeration operates on

Brayton cycle

Rankine’s cycle

Reversed Carnot cycle

Carnot cycle

10. Superheating in a refrigeration cycle

C.O.P remains unaltered

Increases C.O.P

Decreases C.O.P

Other factors decide C.O.P

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

Carbon dioxide

Sulphur dioxide

Ammonia

R-12

12. 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 be lower

Will remain unaffected

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

13. The sub-cooling in a refrigeration cycle

Does not alter C.O.P.

None of these

Increases C.O.P.

Decreases C.O.P.

14. 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

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

Metering of the refrigerant liquid

Condensation of the refrigerant vapour

Evaporation of the refrigerant liquid

Compression of the refrigerant vapour

16. 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 condenser

After passing through the expansion or throttle valve

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

Same as

None of these

Lower than

Higher than

18. Moisture in Freon refrigeration system causes

High power consumption

Corrosion of whole system

Freezing automatic regulating valve

Ineffective refrigeration

19. The specific humidity during dehumidification process

Remains constant

None of these

Decreases

Increases

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

26°C DBT and 60% RH

20°C DBT and 50% RH

26°C DBT and 50% RH

20°C DBT and 60% RH

Page 3 of 5

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

Specific

Relative

None of these

Absolute

22. The Freon group of refrigerants are

Zoetrope refrigerants

Hydrocarbon refrigerants

Halocarbon refrigerants

Inorganic refrigerants

23. 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)/(td₂ - td₃)

(td₃ - td₁)/(td₃ - td₂)

(td₂ - td₃)/(td₃ - td₁)

24. The advantage of dry compression is that

It permits complete evaporation in the evaporator

It permits higher speeds to be used

It results in high volumetric and mechanical efficiency

All of the above

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

Halide torch

Soap and water

Sulphur sticks

All of these

26. During sensible cooling,

Partial pressure of vapour remains constant

Specific humidity increases

Wet bulb temperature increases

Relative humidity remains constant

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

Room sensible heat load only

Room latent heat load only

None of the above

Both room sensible heat and latent heat loads

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

Freon-22

CO2

NH3

Freon-12

29. During cooling and dehumidification, dry bulb temperature

Decreases

Increases

None of these

Remains constant

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

Small

Equal

High

Anything

Page 4 of 5

31. The relative coefficient of performance is

Actual COP × theoretical COP

Theoretical COP/actual COP

Actual COP/theoretical COP

None of these

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

R-12

Ammonia

Carbon dioxide

Sulphur dioxide

33. The superheating in a refrigeration cycle

Decreases C.O.P.

Does not alter C.O.P.

Increases C.O.P.

None of these

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

Less than 2 kg

There is no such consideration

More than 10 kg

More than or equal to 3.65 kg

35. Air conditioning means

Heating

All of these

Cooling

Dehumidifying

36. 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)

37. 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

Decrease

Increase

Remain unaffected

38. Refrigeration in aeroplanes usually employs the following refrigerant

Freon-22

Air

Freon-11

CO2

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

Flooded

Dry

DX coil

None of these

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

Enthalpy increase in compressor

Work done by compressor

All of the above

Heat of compression

Page 5 of 5

41. 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

Mean radiant temperature

Effective temperature

42. 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

1 kW

3 kW

4 kW

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

Wet vapour

Dry saturated vapour

Saturated liquid

Superheated vapour

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

Expansion valve and evaporator

Condenser and expansion valve

Compressor and condenser

Compressor and evaporator

45. 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)]

None of these

μ/[1 - (1 - μ) (Ps/Pb)]

0.622 Pv / (Pb - Pv)

Refrigeration & Air-Conditioning Practice Set-4

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