Refrigeration & Air-Conditioning Practice Set-4

June 7, 2021

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Page 1 of 5

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

Enthalpy increase in compressor

Work done by compressor

Heat of compression

All of the above

2. The relative coefficient of performance is

Theoretical COP/actual COP

Actual COP/theoretical COP

None of these

Actual COP × theoretical COP

3. The Freon group of refrigerants are

Hydrocarbon refrigerants

Inorganic refrigerants

Zoetrope refrigerants

Halocarbon refrigerants

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

Dew point temperature

Mean radiant temperature

None of these

Effective temperature

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

After passing through the condenser

Before entering the compressor

After passing through the expansion or throttle valve

Before passing through the condenser

7. The specific humidity during heating and humidification process.

None of these

Decreases

Increases

Remains constant

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

Remain unaffected

Decrease

May increase or decrease depending on the type of refrigerant used

Increase

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

26°C DBT and 50% RH

20°C DBT and 60% RH

26°C DBT and 60% RH

20°C DBT and 50% RH

10. During cooling and dehumidification, dry bulb temperature

Remains constant

None of these

Increases

Decreases

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11. Superheating in a refrigeration cycle

C.O.P remains unaltered

Other factors decide C.O.P

Decreases C.O.P

Increases C.O.P

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

Relative

Absolute

None of these

Specific

13. 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

14. 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

4 kW

3 kW

1 kW

15. Refrigeration in aeroplanes usually employs the following refrigerant

Air

CO2

Freon-11

Freon-22

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

Direct

Absorption

Compression

Indirect

17. 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)]

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

None of these

0.622 Pv / (Pb - Pv)

18. The superheating in a refrigeration cycle

Does not alter C.O.P.

Increases C.O.P.

None of these

Decreases C.O.P.

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

Saturated liquid

Wet vapour

Dry saturated vapour

Superheated vapour

20. Vapour compression refrigeration is somewhat like

Reversed Carnot cycle

None of the above

Rankine’s cycle

Carnot cycle

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

Small

High

Anything

Equal

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

DX coil

Dry

Flooded

None of these

23. The specific humidity during dehumidification process

Decreases

None of these

Remains constant

Increases

24. Air refrigeration operates on

Reversed Carnot cycle

Carnot cycle

Rankine’s cycle

Brayton cycle

25. 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

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

Mixture of ice and water under equilibrium conditions

Ice at 4°C

Water at 0°C

Solid and dry ice

27. Moisture in Freon refrigeration system causes

Ineffective refrigeration

High power consumption

Corrosion of whole system

Freezing automatic regulating valve

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

All of these

Soap and water

Sulphur sticks

Halide torch

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)

(h2 - hA)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

(hA - h2)/ (h1 - h2)

30. 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

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

Ammonia

R-12

Carbon dioxide

Sulphur dioxide

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

None of the above

Both room sensible heat and latent heat loads

Room sensible heat load only

Room latent heat load only

33. Which of the following statement is correct?

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

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

The constant enthalpy lines are also constant wet bulb temperature lines

All of these

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

Freon-12

CO2

Freon-22

NH3

35. 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 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

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

36. The advantage of dry compression is that

It permits complete evaporation in the evaporator

It results in high volumetric and mechanical efficiency

All of the above

It permits higher speeds to be used

37. Air conditioning means

All of these

Heating

Cooling

Dehumidifying

38. The sub-cooling in a refrigeration cycle

Decreases C.O.P.

Does not alter C.O.P.

Increases C.O.P.

None of these

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

Ammonia

Carbon dioxide

R-12

Sulphur dioxide

40. Ammonia absorption refrigeration cycle requires

Very little work input

Maximum work input

Nearly same work input as for vapour compression cycle

Zero work input

Page 5 of 5

41. During sensible cooling,

Specific humidity increases

Partial pressure of vapour remains constant

Relative humidity remains constant

Wet bulb temperature increases

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

Compressor and evaporator

Expansion valve and evaporator

Compressor and condenser

Condenser and expansion valve

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

Lower than

Higher than

None of these

Same as

44. 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 - td₂)/(td₃ - td₁)

(td₂ - td₃)/(td₃ - td₁)

(td₃ - td₁)/(td₃ - td₂)

45. 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

There is no such consideration

More than 10 kg

Less than 2 kg

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Refrigeration & Air-Conditioning Practice Set-4

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