Refrigeration & Air-Conditioning Practice Set-4

Page 1 of 5

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

After passing through the condenser

Before entering the compressor

Before passing through the condenser

After passing through the expansion or throttle valve

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

Equal

High

Anything

Small

3. 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

4. The specific humidity during dehumidification process

None of these

Decreases

Remains constant

Increases

5. The superheating in a refrigeration cycle

None of these

Increases C.O.P.

Does not alter C.O.P.

Decreases C.O.P.

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

None of these

DX coil

Flooded

Dry

7. During cooling and dehumidification, dry bulb temperature

Remains constant

None of these

Increases

Decreases

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

Wet vapour

Superheated vapour

Dry saturated vapour

Saturated liquid

9. Air conditioning means

Heating

Cooling

All of these

Dehumidifying

10. Air refrigeration operates on

Brayton cycle

Rankine’s cycle

Carnot cycle

Reversed Carnot cycle

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11. During sensible cooling,

Partial pressure of vapour remains constant

Specific humidity increases

Wet bulb temperature increases

Relative humidity remains constant

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

NH3

Freon-22

CO2

Freon-12

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

Water at 0°C

Solid and dry ice

Mixture of ice and water under equilibrium conditions

Ice at 4°C

14. Superheating in a refrigeration cycle

Other factors decide C.O.P

Increases C.O.P

C.O.P remains unaltered

Decreases C.O.P

15. 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

μ/[1 - (1 - μ) (Ps/Pb)]

0.622 Pv / (Pb - Pv)

16. 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

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

Compressor and evaporator

Condenser and expansion valve

Compressor and condenser

Expansion valve and evaporator

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

Same

Less

More

More or less depending on ambient conditions

19. The advantage of dry compression is that

It results in high volumetric and mechanical efficiency

It permits complete evaporation in the evaporator

All of the above

It permits higher speeds to be used

20. 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)

(td₂ - td₃)/(td₃ - td₁)

(td₃ - td₁)/(td₃ - td₂)

(td₃ - td₂)/(td₃ - td₁)

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21. 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

5

6

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

R-12

Sulphur dioxide

Ammonia

Carbon dioxide

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

Carbon dioxide

Ammonia

Sulphur dioxide

R-12

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

Condensation of the refrigerant vapour

Metering of the refrigerant liquid

Evaporation of the refrigerant liquid

Compression of the refrigerant vapour

25. The Freon group of refrigerants are

Inorganic refrigerants

Hydrocarbon refrigerants

Zoetrope refrigerants

Halocarbon refrigerants

26. Which of the following statement is correct?

The constant enthalpy lines are also constant wet bulb temperature lines

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

All of these

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

27. Refrigeration in aeroplanes usually employs the following refrigerant

CO2

Air

Freon-11

Freon-22

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

Soap and water

All of these

Halide torch

Sulphur sticks

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)

(hA - h2)/ (h1 - h2)

(h2 - hA)/ (h1 - h2)

(hA - h1)/ (h2 - h1)

(h1 - h2)/ (hA - h2)

30. 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

None of these

Mean radiant temperature

Page 4 of 5

31. The sub-cooling in a refrigeration cycle

Increases C.O.P.

Does not alter C.O.P.

None of these

Decreases C.O.P.

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

Room latent heat load only

Room sensible heat load only

None of the above

Both room sensible heat and latent heat loads

33. Moisture in Freon refrigeration system causes

Freezing automatic regulating valve

High power consumption

Corrosion of whole system

Ineffective refrigeration

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

26°C DBT and 50% RH

26°C DBT and 60% RH

20°C DBT and 60% RH

20°C DBT and 50% RH

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

Compression

Absorption

Direct

Indirect

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

Decrease

May increase or decrease depending on the type of refrigerant used

Increase

Remain unaffected

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

Work done by compressor

Enthalpy increase in compressor

Heat of compression

All of the above

38. Ammonia absorption refrigeration cycle requires

Zero work input

Very little work input

Nearly same work input as for vapour compression cycle

Maximum work input

39. The specific humidity during heating and humidification process.

None of these

Increases

Remains constant

Decreases

40. The relative coefficient of performance is

Actual COP × theoretical COP

Actual COP/theoretical COP

Theoretical COP/actual COP

None of these

Page 5 of 5

41. 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

3 kW

1 kW

4 kW

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

None of these

Higher than

Same as

Lower than

43. Vapour compression refrigeration is somewhat like

Rankine’s cycle

None of the above

Reversed Carnot cycle

Carnot cycle

44. 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

Will remain unaffected

Will be higher

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

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

Specific

Relative

None of these

Absolute

Refrigeration & Air-Conditioning Practice Set-4

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