Refrigeration & Air-Conditioning Practice Set-4

June 7, 2021

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Page 1 of 5

1. The specific humidity during heating and humidification process.

Remains constant

None of these

Increases

Decreases

2. 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

3. Air conditioning means

All of these

Heating

Cooling

Dehumidifying

4. 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)

(hA - h2)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

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

Remain unaffected

Increase

Decrease

May increase or decrease depending on the type of refrigerant used

6. 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

7. 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)]

None of these

0.622 Pv / (Pb - Pv)

μ/[1 - (1 - μ) (Ps/Pb)]

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

Sulphur dioxide

Ammonia

Carbon dioxide

R-12

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

20°C DBT and 50% RH

20°C DBT and 60% RH

26°C DBT and 50% RH

26°C DBT and 60% RH

10. 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 10 kg

More than or equal to 3.65 kg

Less than 2 kg

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

Small

Equal

High

Anything

12. During cooling and dehumidification, dry bulb temperature

None of these

Increases

Decreases

Remains constant

13. The superheating in a refrigeration cycle

None of these

Does not alter C.O.P.

Increases C.O.P.

Decreases C.O.P.

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

Dry saturated vapour

Superheated vapour

Wet vapour

Saturated liquid

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

Sulphur dioxide

Carbon dioxide

R-12

Ammonia

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

Condenser and expansion valve

Expansion valve and evaporator

Compressor and condenser

Compressor and evaporator

17. Vapour compression refrigeration is somewhat like

Rankine’s cycle

Reversed Carnot cycle

Carnot cycle

None of the above

18. The sub-cooling in a refrigeration cycle

Decreases C.O.P.

Increases C.O.P.

Does not alter C.O.P.

None of these

19. 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

20. Air refrigeration operates on

Brayton cycle

Rankine’s cycle

Carnot cycle

Reversed Carnot cycle

Page 3 of 5

21. The specific humidity during dehumidification process

Decreases

Increases

None of these

Remains constant

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

Room sensible heat load only

Room latent heat load only

Both room sensible heat and latent heat loads

None of the above

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

DX coil

Dry

None of these

Flooded

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

CO2

Freon-12

NH3

Freon-22

25. 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

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

Before entering the compressor

After passing through the expansion or throttle valve

Before passing through the condenser

After passing through the condenser

27. 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

28. The relative coefficient of performance is

Actual COP/theoretical COP

Actual COP × theoretical COP

None of these

Theoretical COP/actual COP

29. During sensible cooling,

Wet bulb temperature increases

Specific humidity increases

Partial pressure of vapour remains constant

Relative humidity remains constant

30. Ammonia absorption refrigeration cycle requires

Very little work input

Nearly same work input as for vapour compression cycle

Maximum work input

Zero work input

Page 4 of 5

31. The Freon group of refrigerants are

Zoetrope refrigerants

Hydrocarbon refrigerants

Halocarbon refrigerants

Inorganic refrigerants

32. 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

33. Refrigeration in aeroplanes usually employs the following refrigerant

Freon-22

Air

CO2

Freon-11

34. 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

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

Effective temperature

Mean radiant temperature

None of these

Dew point temperature

37. The advantage of dry compression is that

It permits complete evaporation in the evaporator

All of the above

It permits higher speeds to be used

It results in high volumetric and mechanical efficiency

38. Moisture in Freon refrigeration system causes

Freezing automatic regulating valve

Corrosion of whole system

High power consumption

Ineffective refrigeration

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

Absolute

Specific

Relative

None of these

40. 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 - td₁)/(td₂ - td₃)

(td₃ - td₂)/(td₃ - td₁)

(td₃ - td₁)/(td₃ - td₂)

Page 5 of 5

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

Same as

Lower than

None of these

Higher than

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

Compression

Direct

Indirect

Absorption

43. Superheating in a refrigeration cycle

Increases C.O.P

Other factors decide C.O.P

Decreases C.O.P

C.O.P remains unaltered

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

All of these

Sulphur sticks

Soap and water

Halide torch

45. 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

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

Will be higher

Will be lower

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Refrigeration & Air-Conditioning Practice Set-4

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