Refrigeration & Air-Conditioning Practice Set-4

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

Before entering the compressor

After passing through the condenser

Before passing through the condenser

After passing through the expansion or throttle valve

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

Absolute

Specific

Relative

None of these

3. 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

4. The superheating in a refrigeration cycle

Decreases C.O.P.

Does not alter C.O.P.

Increases C.O.P.

None of these

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

More

Less

More or less depending on ambient conditions

Same

6. The advantage of dry compression is that

It permits complete evaporation in the evaporator

It results in high volumetric and mechanical efficiency

All of the above

It permits higher speeds to be used

7. The specific humidity during dehumidification process

Increases

Remains constant

Decreases

None of these

8. Which of the following statement is correct?

The constant enthalpy lines are also constant wet bulb temperature lines

All of these

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

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

9. Air conditioning means

All of these

Dehumidifying

Heating

Cooling

10. 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

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

May increase or decrease depending on the type of refrigerant used

Increase

Decrease

Remain unaffected

12. Ammonia absorption refrigeration cycle requires

Maximum work input

Very little work input

Zero work input

Nearly same work input as for vapour compression cycle

13. The specific humidity during heating and humidification process.

None of these

Increases

Decreases

Remains constant

14. Refrigeration in aeroplanes usually employs the following refrigerant

Freon-11

Air

CO2

Freon-22

15. 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)

(td₃ - td₁)/(td₂ - td₃)

(td₂ - td₃)/(td₃ - td₁)

16. The Freon group of refrigerants are

Zoetrope refrigerants

Halocarbon refrigerants

Hydrocarbon refrigerants

Inorganic refrigerants

17. The sub-cooling in a refrigeration cycle

None of these

Decreases C.O.P.

Increases C.O.P.

Does not alter C.O.P.

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

DX coil

None of these

Dry

Flooded

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

Small

Anything

Equal

High

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

Metering of the refrigerant liquid

Condensation of the refrigerant vapour

Compression of the refrigerant vapour

Evaporation of the refrigerant liquid

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21. Superheating in a refrigeration cycle

Other factors decide C.O.P

C.O.P remains unaltered

Decreases C.O.P

Increases C.O.P

22. 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

3 kW

2 kW

1 kW

23. Vapour compression refrigeration is somewhat like

None of the above

Carnot cycle

Reversed Carnot cycle

Rankine’s cycle

24. 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 higher

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

Will remain unaffected

Will be lower

25. 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

Of adiabatic saturation of incoming stream

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

26. The relative coefficient of performance is

None of these

Actual COP × theoretical COP

Actual COP/theoretical COP

Theoretical COP/actual COP

27. Moisture in Freon refrigeration system causes

Corrosion of whole system

Ineffective refrigeration

High power consumption

Freezing automatic regulating valve

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

Freon-22

Freon-12

CO2

NH3

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

Sulphur dioxide

Carbon dioxide

R-12

Ammonia

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

Same as

Lower than

Higher than

None of these

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

Superheated vapour

Saturated liquid

Dry saturated vapour

Wet vapour

32. During sensible cooling,

Specific humidity increases

Wet bulb temperature increases

Relative humidity remains constant

Partial pressure of vapour remains constant

33. During cooling and dehumidification, dry bulb temperature

Increases

None of these

Decreases

Remains constant

34. 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)

None of these

μ/[1 - (1 - μ) (Ps/Pb)]

0.622 Pv / (Pb - Pv)

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

35. 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)

(h1 - h2)/ (hA - h2)

(hA - h1)/ (h2 - h1)

(hA - h2)/ (h1 - h2)

36. Air refrigeration operates on

Brayton cycle

Reversed Carnot cycle

Carnot cycle

Rankine’s cycle

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

More than 10 kg

Less than 2 kg

More than or equal to 3.65 kg

There is no such consideration

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

None of these

Dew point temperature

Mean radiant temperature

Effective temperature

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

Water at 0°C

Mixture of ice and water under equilibrium conditions

Ice at 4°C

Solid and dry ice

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

Condenser and expansion valve

Compressor and condenser

Compressor and evaporator

Expansion valve and evaporator

Page 5 of 5

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

Sulphur sticks

All of these

Soap and water

Halide torch

42. 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

6

5

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

Absorption

Compression

Indirect

Direct

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

20°C DBT and 60% RH

26°C DBT and 50% RH

26°C DBT and 60% RH

20°C DBT and 50% RH

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

Sulphur dioxide

R-12

Ammonia

Carbon dioxide

Refrigeration & Air-Conditioning Practice Set-4

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