Refrigeration & Air-Conditioning Practice Set-4

June 7, 2021

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1. Superheating in a refrigeration cycle

Decreases C.O.P

Other factors decide C.O.P

Increases C.O.P

C.O.P remains unaltered

2. The relative coefficient of performance is

Actual COP/theoretical COP

None of these

Theoretical COP/actual COP

Actual COP × theoretical COP

3. 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

4. The sub-cooling in a refrigeration cycle

Decreases C.O.P.

Does not alter C.O.P.

None of these

Increases C.O.P.

5. The superheating in a refrigeration cycle

Increases C.O.P.

None of these

Decreases C.O.P.

Does not alter C.O.P.

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

Equal

Anything

Small

High

7. 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

8. The Freon group of refrigerants are

Halocarbon refrigerants

Inorganic refrigerants

Zoetrope refrigerants

Hydrocarbon refrigerants

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)

(td₂ - td₃)/(td₃ - td₁)

(td₃ - td₂)/(td₃ - td₁)

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11. Refrigeration in aeroplanes usually employs the following refrigerant

CO2

Freon-22

Freon-11

Air

12. 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

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

0.622 Pv / (Pb - Pv)

μ/[1 - (1 - μ) (Ps/Pb)]

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

Sulphur dioxide

R-12

Carbon dioxide

Ammonia

14. Ammonia absorption refrigeration cycle requires

Maximum work input

Zero work input

Very little work input

Nearly same work input as for vapour compression cycle

15. 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 remain unaffected

Will be lower

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

Will be higher

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

Room latent heat load only

Both room sensible heat and latent heat loads

None of the above

Room sensible heat load only

17. Which of the following statement is correct?

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

All of these

The constant enthalpy lines are also constant wet bulb temperature lines

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

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

After passing through the expansion or throttle valve

Before entering the compressor

After passing through the condenser

Before passing through the condenser

19. 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

20. Vapour compression refrigeration is somewhat like

Reversed Carnot cycle

None of the above

Rankine’s cycle

Carnot cycle

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21. Air refrigeration operates on

Reversed Carnot cycle

Carnot cycle

Rankine’s cycle

Brayton cycle

22. Air conditioning means

Heating

All of these

Dehumidifying

Cooling

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

26°C DBT and 50% RH

26°C DBT and 60% RH

20°C DBT and 50% RH

20°C DBT and 60% RH

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

Compression

Direct

Absorption

Indirect

25. 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

Of adiabatic saturation of 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

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

Ammonia

Carbon dioxide

Sulphur dioxide

R-12

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

None of these

Relative

Absolute

Specific

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

Work done by compressor

Enthalpy increase in compressor

All of the above

Heat of compression

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

Sulphur sticks

All of these

Halide torch

Soap and water

30. Moisture in Freon refrigeration system causes

Corrosion of whole system

Freezing automatic regulating valve

Ineffective refrigeration

High power consumption

Page 4 of 5

31. During cooling and dehumidification, dry bulb temperature

Remains constant

Increases

Decreases

None of these

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

DX coil

Dry

None of these

Flooded

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

None of these

Higher than

Same as

Lower than

34. 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)

(h2 - hA)/ (h1 - h2)

(hA - h2)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

(hA - h1)/ (h2 - h1)

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

Water at 0°C

Mixture of ice and water under equilibrium conditions

Solid and dry ice

Ice at 4°C

36. During sensible cooling,

Specific humidity increases

Wet bulb temperature increases

Relative humidity remains constant

Partial pressure of vapour remains constant

37. The specific humidity during heating and humidification process.

Increases

None of these

Remains constant

Decreases

38. The advantage of dry compression is that

It results in high volumetric and mechanical efficiency

It permits complete evaporation in the evaporator

All of the above

It permits higher speeds to be used

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

Wet vapour

Saturated liquid

Superheated vapour

Dry saturated vapour

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

CO2

Freon-12

NH3

Freon-22

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

Less than 2 kg

More than 10 kg

More than or equal to 3.65 kg

There is no such consideration

42. The specific humidity during dehumidification process

None of these

Increases

Decreases

Remains constant

43. 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

1 kW

2 kW

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

Compression of the refrigerant vapour

Condensation of the refrigerant vapour

Metering of the refrigerant liquid

Evaporation of the refrigerant liquid

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

Compressor and condenser

Expansion valve and evaporator

Condenser and expansion valve

Compressor and evaporator

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