Refrigeration & Air-Conditioning Practice Set-4

Page 1 of 5

1. Vapour compression refrigeration is somewhat like

Rankine’s cycle

Reversed Carnot cycle

None of the above

Carnot cycle

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

CO2

Freon-22

Freon-12

NH3

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

26°C DBT and 60% RH

20°C DBT and 50% RH

20°C DBT and 60% RH

26°C DBT and 50% RH

4. 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

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

Direct

Absorption

Indirect

Compression

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

Superheated vapour

Dry saturated vapour

Wet vapour

Saturated liquid

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

None of these

Higher than

Lower than

Same as

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

Sulphur dioxide

Ammonia

Carbon dioxide

R-12

9. Air refrigeration operates on

Rankine’s cycle

Reversed Carnot cycle

Brayton cycle

Carnot cycle

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

More or less depending on ambient conditions

Less

More

Same

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11. The relative coefficient of performance is

None of these

Actual COP/theoretical COP

Theoretical COP/actual COP

Actual COP × theoretical COP

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

Specific

Relative

Absolute

None of these

13. During sensible cooling,

Wet bulb temperature increases

Specific humidity increases

Relative humidity remains constant

Partial pressure of vapour remains constant

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

Evaporation of the refrigerant liquid

Condensation of the refrigerant vapour

Compression of the refrigerant vapour

Metering of the refrigerant liquid

15. During cooling and dehumidification, dry bulb temperature

Increases

None of these

Decreases

Remains constant

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

Mixture of ice and water under equilibrium conditions

Solid and dry ice

Ice at 4°C

Water at 0°C

17. 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

5

6

0.2

1.2

18. Refrigeration in aeroplanes usually employs the following refrigerant

Freon-11

Freon-22

CO2

Air

19. The specific humidity during dehumidification process

None of these

Remains constant

Decreases

Increases

20. The specific humidity during heating and humidification process.

Decreases

Increases

Remains constant

None of these

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

Anything

Equal

High

Small

22. 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

23. The sub-cooling in a refrigeration cycle

None of these

Decreases C.O.P.

Increases C.O.P.

Does not alter C.O.P.

24. Which of the following statement is correct?

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

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

All of these

The constant enthalpy lines are also constant wet bulb temperature lines

25. 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)

μ/[1 - (1 - μ) (Ps/Pb)]

None of these

0.622 Pv / (Pb - Pv)

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

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

None of the above

Room sensible heat load only

Both room sensible heat and latent heat loads

Room latent heat load only

27. Moisture in Freon refrigeration system causes

High power consumption

Corrosion of whole system

Ineffective refrigeration

Freezing automatic regulating valve

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

Less than 2 kg

There is no such consideration

More than or equal to 3.65 kg

More than 10 kg

29. 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)

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

Increase

Decrease

Remain unaffected

May increase or decrease depending on the type of refrigerant used

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31. 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

4 kW

1 kW

3 kW

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

Enthalpy increase in compressor

Work done by compressor

Heat of compression

All of the above

33. Air conditioning means

Dehumidifying

Cooling

All of these

Heating

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

Halide torch

All of these

Sulphur sticks

Soap and water

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

Sulphur dioxide

R-12

Ammonia

Carbon dioxide

36. Ammonia absorption refrigeration cycle requires

Nearly same work input as for vapour compression cycle

Very little work input

Zero work input

Maximum work input

37. In order to cool and dehumidify a stream of moist air, it must be passed over the coil at a temperature

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

Which lies between the wet bulb and dew point temperatures of the incoming stream

Of adiabatic saturation of incoming stream

38. The Freon group of refrigerants are

Halocarbon refrigerants

Hydrocarbon refrigerants

Inorganic refrigerants

Zoetrope refrigerants

39. 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

None of these

Effective temperature

Mean radiant temperature

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)

(td₃ - td₁)/(td₂ - td₃)

(td₃ - td₂)/(td₃ - td₁)

(td₂ - td₃)/(td₃ - td₁)

(td₃ - td₁)/(td₃ - td₂)

Page 5 of 5

41. The superheating in a refrigeration cycle

Increases C.O.P.

Does not alter C.O.P.

None of these

Decreases C.O.P.

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

Flooded

Dry

None of these

DX coil

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

Expansion valve and evaporator

Condenser and expansion valve

Compressor and condenser

Compressor and evaporator

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

After passing through the expansion or throttle valve

Before passing through the condenser

Before entering the compressor

After passing through the condenser

45. Superheating in a refrigeration cycle

Increases C.O.P

C.O.P remains unaltered

Other factors decide C.O.P

Decreases C.O.P

Refrigeration & Air-Conditioning Practice Set-4

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