Refrigeration & Air-Conditioning Practice Set-4

June 7, 2021

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Page 1 of 5

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

Absolute

None of these

Relative

Specific

2. The Freon group of refrigerants are

Hydrocarbon refrigerants

Zoetrope refrigerants

Inorganic refrigerants

Halocarbon refrigerants

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

Saturated liquid

Wet vapour

Superheated vapour

Dry saturated vapour

4. During cooling and dehumidification, dry bulb temperature

None of these

Remains constant

Increases

Decreases

5. 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

6. The specific humidity during heating and humidification process.

None of these

Increases

Remains constant

Decreases

7. The advantage of dry compression is that

All of the above

It permits higher speeds to be used

It permits complete evaporation in the evaporator

It results in high volumetric and mechanical efficiency

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

There is no such consideration

Less than 2 kg

More than or equal to 3.65 kg

More than 10 kg

9. 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

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 - td₂)/(td₃ - td₁)

(td₂ - td₃)/(td₃ - td₁)

(td₃ - td₁)/(td₂ - td₃)

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11. Which of the following statement is correct?

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

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

The constant enthalpy lines are also constant wet bulb temperature lines

All of these

12. The sub-cooling in a refrigeration cycle

None of these

Increases C.O.P.

Does not alter C.O.P.

Decreases C.O.P.

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

Direct

Absorption

Indirect

Compression

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

Flooded

Dry

DX coil

None of these

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

All of these

Sulphur sticks

Soap and water

Halide torch

16. Superheating in a refrigeration cycle

C.O.P remains unaltered

Increases C.O.P

Decreases C.O.P

Other factors decide C.O.P

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

Evaporation of the refrigerant liquid

Condensation of the refrigerant vapour

Metering of the refrigerant liquid

Compression of the refrigerant vapour

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

Carbon dioxide

Sulphur dioxide

R-12

Ammonia

19. The specific humidity during dehumidification process

Remains constant

Increases

None of these

Decreases

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

Enthalpy increase in compressor

All of the above

Heat of compression

Work done by compressor

Page 3 of 5

21. 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)

(h1 - h2)/ (hA - h2)

(hA - h2)/ (h1 - h2)

(h2 - hA)/ (h1 - h2)

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

Solid and dry ice

Water at 0°C

Mixture of ice and water under equilibrium conditions

Ice at 4°C

23. During sensible cooling,

Relative humidity remains constant

Specific humidity increases

Partial pressure of vapour remains constant

Wet bulb temperature increases

24. 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)

0.622 Pv / (Pb - Pv)

None of these

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

μ/[1 - (1 - μ) (Ps/Pb)]

25. Ammonia absorption refrigeration cycle requires

Very little work input

Zero work input

Maximum work input

Nearly same work input as for vapour compression cycle

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

Less

Same

More or less depending on ambient conditions

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

Compressor and condenser

Compressor and evaporator

Expansion valve and evaporator

Condenser and expansion valve

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

None of the above

Room latent heat load only

Room sensible heat load only

Both room sensible heat and latent heat loads

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

Lower than

Same as

None of these

Higher than

30. Vapour compression refrigeration is somewhat like

Rankine’s cycle

Carnot cycle

Reversed Carnot cycle

None of the above

Page 4 of 5

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

Sulphur dioxide

Ammonia

Carbon dioxide

R-12

32. Air refrigeration operates on

Reversed Carnot cycle

Brayton cycle

Rankine’s cycle

Carnot cycle

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

26°C DBT and 60% RH

26°C DBT and 50% RH

20°C DBT and 60% RH

20°C DBT and 50% RH

34. 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 remain unaffected

Will be higher

Will be lower

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

Freon-22

NH3

CO2

Freon-12

36. The relative coefficient of performance is

Theoretical COP/actual COP

None of these

Actual COP × theoretical COP

Actual COP/theoretical COP

37. Air conditioning means

Dehumidifying

Cooling

Heating

All of these

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

Decrease

Remain unaffected

May increase or decrease depending on the type of refrigerant used

Increase

39. Moisture in Freon refrigeration system causes

Ineffective refrigeration

High power consumption

Corrosion of whole system

Freezing automatic regulating valve

40. 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

Page 5 of 5

41. The superheating in a refrigeration cycle

None of these

Decreases C.O.P.

Increases C.O.P.

Does not alter C.O.P.

42. 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 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

Of adiabatic saturation of incoming stream

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

Anything

High

Small

Equal

44. Refrigeration in aeroplanes usually employs the following refrigerant

CO2

Air

Freon-11

Freon-22

45. 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 expansion or throttle valve

After passing through the condenser

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Refrigeration & Air-Conditioning Practice Set-4

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