Refrigeration & Air-Conditioning Practice Set-4

June 7, 2021

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Page 1 of 5

1. 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

2. Ammonia absorption refrigeration cycle requires

Very little work input

Nearly same work input as for vapour compression cycle

Zero work input

Maximum work input

3. Refrigeration in aeroplanes usually employs the following refrigerant

CO2

Freon-22

Freon-11

Air

4. Vapour compression refrigeration is somewhat like

Rankine’s cycle

Carnot cycle

None of the above

Reversed Carnot cycle

5. 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 is lower than the dew point temperature of the incoming stream

Which lies between the dry bulb and wet bulb temperatures of the incoming stream

Of adiabatic saturation of incoming stream

6. 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 10 kg

More than or equal to 3.65 kg

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

Decrease

Increase

Remain unaffected

May increase or decrease depending on the type of refrigerant used

8. Air conditioning means

Dehumidifying

Cooling

All of these

Heating

9. Superheating in a refrigeration cycle

C.O.P remains unaltered

Decreases C.O.P

Increases C.O.P

Other factors decide C.O.P

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

Sulphur dioxide

R-12

Carbon dioxide

Ammonia

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11. Moisture in Freon refrigeration system causes

Corrosion of whole system

Ineffective refrigeration

Freezing automatic regulating valve

High power consumption

12. 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)/(td₃ - td₂)

(td₂ - td₃)/(td₃ - td₁)

(td₃ - td₁)/(td₂ - td₃)

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

Sulphur sticks

All of these

Halide torch

Soap and water

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

Condenser and expansion valve

Compressor and evaporator

Compressor and condenser

Expansion valve and evaporator

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

Absorption

Direct

Compression

Indirect

16. 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

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

Saturated liquid

Superheated vapour

Dry saturated vapour

Wet vapour

18. 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)

(h1 - h2)/ (hA - h2)

(hA - h1)/ (h2 - h1)

(h2 - hA)/ (h1 - h2)

(hA - h2)/ (h1 - h2)

19. During sensible cooling,

Specific humidity increases

Wet bulb temperature increases

Partial pressure of vapour remains constant

Relative humidity remains constant

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

20°C DBT and 50% RH

26°C DBT and 60% RH

20°C DBT and 60% RH

26°C DBT and 50% RH

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21. The specific humidity during dehumidification process

Decreases

None of these

Remains constant

Increases

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

All of the above

Enthalpy increase in compressor

Heat of compression

Work done by compressor

23. The Freon group of refrigerants are

Zoetrope refrigerants

Hydrocarbon refrigerants

Inorganic refrigerants

Halocarbon refrigerants

24. The sub-cooling in a refrigeration cycle

None of these

Decreases C.O.P.

Does not alter C.O.P.

Increases C.O.P.

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

Equal

Small

High

Anything

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

Sulphur dioxide

Ammonia

Carbon dioxide

R-12

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

None of these

Lower than

Same as

Higher than

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

Room latent heat load only

Room sensible heat load only

Both room sensible heat and latent heat loads

None of the above

29. 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 remain unaffected

Will be lower

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

None of these

Relative

Absolute

Specific

Page 4 of 5

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

Mixture of ice and water under equilibrium conditions

Water at 0°C

Ice at 4°C

Solid and dry ice

32. The superheating in a refrigeration cycle

Decreases C.O.P.

Does not alter C.O.P.

None of these

Increases C.O.P.

33. 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

34. 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

35. Air refrigeration operates on

Brayton cycle

Rankine’s cycle

Reversed Carnot cycle

Carnot cycle

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

Before entering the compressor

After passing through the condenser

After passing through the expansion or throttle valve

Before passing through the condenser

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

Condensation of the refrigerant vapour

Compression of the refrigerant vapour

Evaporation of the refrigerant liquid

Metering of the refrigerant liquid

38. During cooling and dehumidification, dry bulb temperature

Decreases

Increases

Remains constant

None of these

39. The relative coefficient of performance is

None of these

Actual COP/theoretical COP

Actual COP × theoretical COP

Theoretical COP/actual COP

40. The advantage of dry compression is that

It results in high volumetric and mechanical efficiency

It permits higher speeds to be used

All of the above

It permits complete evaporation in the evaporator

Page 5 of 5

41. The specific humidity during heating and humidification process.

Remains constant

None of these

Increases

Decreases

42. 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

Effective temperature

Mean radiant temperature

None of these

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

Freon-22

NH3

Freon-12

CO2

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

Dry

None of these

Flooded

DX coil

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)]

μ/[1 - (1 - μ) (Ps/Pb)]

None of these

0.622 Pv / (Pb - Pv)

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Refrigeration & Air-Conditioning Practice Set-4

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