Refrigeration & Air-Conditioning Practice Set-4

June 7, 2021

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Page 1 of 5

1. The superheating in a refrigeration cycle

None of these

Decreases C.O.P.

Increases C.O.P.

Does not alter C.O.P.

2. The relative coefficient of performance is

None of these

Actual COP × theoretical COP

Actual COP/theoretical COP

Theoretical COP/actual COP

3. Vapour compression refrigeration is somewhat like

Rankine’s cycle

None of the above

Carnot cycle

Reversed Carnot cycle

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

20°C DBT and 60% RH

26°C DBT and 50% RH

20°C DBT and 50% RH

26°C DBT and 60% RH

5. 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 - td₂)/(td₃ - td₁)

(td₃ - td₁)/(td₃ - td₂)

(td₃ - td₁)/(td₂ - td₃)

6. The advantage of dry compression is that

It permits higher speeds to be used

All of the above

It results in high volumetric and mechanical efficiency

It permits complete evaporation in the evaporator

7. The specific humidity during heating and humidification process.

Decreases

None of these

Remains constant

Increases

8. 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

9. Moisture in Freon refrigeration system causes

Freezing automatic regulating valve

Corrosion of whole system

High power consumption

Ineffective refrigeration

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

Both room sensible heat and latent heat loads

Room latent heat load only

Room sensible heat load only

None of the above

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11. 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

12. 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

Dew point temperature

Effective temperature

None of these

13. 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 or equal to 3.65 kg

Less than 2 kg

More than 10 kg

14. 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

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

Will remain unaffected

Will be higher

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

R-12

Ammonia

Carbon dioxide

Sulphur dioxide

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

Lower than

Higher than

Same as

None of these

17. Superheating in a refrigeration cycle

Increases C.O.P

Decreases C.O.P

C.O.P remains unaltered

Other factors decide C.O.P

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

Increase

Remain unaffected

May increase or decrease depending on the type of refrigerant used

Decrease

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

After passing through the expansion or throttle valve

After passing through the condenser

Before entering the compressor

Before passing through the condenser

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

Small

Anything

High

Equal

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

Compression of the refrigerant vapour

Evaporation of the refrigerant liquid

Metering of the refrigerant liquid

Condensation of the refrigerant vapour

22. Refrigeration in aeroplanes usually employs the following refrigerant

CO2

Freon-22

Freon-11

Air

23. Air refrigeration operates on

Brayton cycle

Carnot cycle

Reversed Carnot cycle

Rankine’s cycle

24. 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)

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

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

26. Air conditioning means

All of these

Heating

Cooling

Dehumidifying

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

Solid and dry ice

Ice at 4°C

Mixture of ice and water under equilibrium conditions

Water at 0°C

28. The sub-cooling in a refrigeration cycle

Decreases C.O.P.

Increases C.O.P.

Does not alter C.O.P.

None of these

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

Dry

DX coil

None of these

Flooded

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

Absorption

Indirect

Compression

Direct

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

NH3

CO2

Freon-12

Freon-22

32. The specific humidity during dehumidification process

Remains constant

None of these

Decreases

Increases

33. During sensible cooling,

Relative humidity remains constant

Specific humidity increases

Partial pressure of vapour remains constant

Wet bulb temperature increases

34. 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

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

None of these

Specific

Absolute

Relative

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

Carbon dioxide

R-12

Ammonia

Sulphur dioxide

37. During cooling and dehumidification, dry bulb temperature

Remains constant

Decreases

None of these

Increases

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

Expansion valve and evaporator

Compressor and condenser

Condenser and expansion valve

Compressor and evaporator

39. Ammonia absorption refrigeration cycle requires

Zero work input

Maximum work input

Nearly same work input as for vapour compression cycle

Very little work input

40. The Freon group of refrigerants are

Zoetrope refrigerants

Inorganic refrigerants

Hydrocarbon refrigerants

Halocarbon refrigerants

Page 5 of 5

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

Wet vapour

Dry saturated vapour

Superheated vapour

Saturated liquid

42. 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

μ/[1 - (1 - μ) (Ps/Pb)]

0.622 Pv / (Pb - Pv)

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

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

3 kW

2 kW

4 kW

1 kW

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

Heat of compression

Enthalpy increase in compressor

Work done by compressor

All of the above

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

Sulphur sticks

Halide torch

All of these

Soap and water

Refrigeration & Air-Conditioning Practice Set-4

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