Refrigeration & Air-Conditioning Practice Set-4

Page 1 of 5

1. Which of the following statement is correct?

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

All of these

2. Vapour compression refrigeration is somewhat like

Carnot cycle

None of the above

Reversed Carnot cycle

Rankine’s cycle

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

Halide torch

Soap and water

All of these

Sulphur sticks

4. 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

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

None of these

Absolute

Relative

Specific

6. Superheating in a refrigeration cycle

Decreases C.O.P

Increases C.O.P

Other factors decide C.O.P

C.O.P remains unaltered

7. The sub-cooling in a refrigeration cycle

Does not alter C.O.P.

None of these

Increases C.O.P.

Decreases C.O.P.

8. Air refrigeration operates on

Reversed Carnot cycle

Carnot cycle

Rankine’s cycle

Brayton cycle

9. During sensible cooling,

Partial pressure of vapour remains constant

Relative humidity remains constant

Specific humidity increases

Wet bulb temperature increases

10. 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

Page 2 of 5

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

Lower than

Higher than

Same as

None of these

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

Direct

Compression

Absorption

Indirect

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

Dry saturated vapour

Saturated liquid

Superheated vapour

Wet vapour

14. 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

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

Ice at 4°C

Water at 0°C

Mixture of ice and water under equilibrium conditions

Solid and dry ice

16. 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

17. 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)

0.622 Pv / (Pb - Pv)

None of these

μ/[1 - (1 - μ) (Ps/Pb)]

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

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)

(hA - h1)/ (h2 - h1)

(hA - h2)/ (h1 - h2)

(h2 - hA)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

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

Less than 2 kg

More than 10 kg

More than or equal to 3.65 kg

There is no such consideration

20. The relative coefficient of performance is

Actual COP/theoretical COP

None of these

Theoretical COP/actual COP

Actual COP × theoretical COP

Page 3 of 5

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

20°C DBT and 60% RH

26°C DBT and 60% RH

26°C DBT and 50% RH

20°C DBT and 50% RH

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

None of the above

Both room sensible heat and latent heat loads

Room latent heat load only

Room sensible heat load only

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

Carbon dioxide

Ammonia

Sulphur dioxide

R-12

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

Freon-12

Freon-22

CO2

NH3

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

Compressor and condenser

Compressor and evaporator

Expansion valve and evaporator

Condenser and expansion valve

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

Anything

High

Equal

Small

27. Air conditioning means

Heating

Dehumidifying

All of these

Cooling

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

Mean radiant temperature

Effective temperature

None of these

Dew point temperature

29. Moisture in Freon refrigeration system causes

High power consumption

Ineffective refrigeration

Freezing automatic regulating valve

Corrosion of whole system

30. The specific humidity during dehumidification process

Decreases

Increases

Remains constant

None of these

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31. 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

Of adiabatic saturation of incoming stream

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

32. 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

33. During cooling and dehumidification, dry bulb temperature

Remains constant

None of these

Decreases

Increases

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

Work done by compressor

Heat of compression

Enthalpy increase in compressor

All of the above

35. 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

Will be higher

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

Will be lower

36. The Freon group of refrigerants are

Zoetrope refrigerants

Hydrocarbon refrigerants

Inorganic refrigerants

Halocarbon refrigerants

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

Carbon dioxide

Ammonia

R-12

Sulphur dioxide

38. Ammonia absorption refrigeration cycle requires

Very little work input

Zero work input

Maximum work input

Nearly same work input as for vapour compression cycle

39. The specific humidity during heating and humidification process.

Remains constant

None of these

Increases

Decreases

40. The superheating in a refrigeration cycle

None of these

Does not alter C.O.P.

Increases C.O.P.

Decreases C.O.P.

Page 5 of 5

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

More

Less

Same

More or less depending on ambient conditions

42. 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)

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

Remain unaffected

Decrease

May increase or decrease depending on the type of refrigerant used

Increase

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

Dry

Flooded

DX coil

None of these

45. Refrigeration in aeroplanes usually employs the following refrigerant

Freon-11

CO2

Air

Freon-22

Refrigeration & Air-Conditioning Practice Set-4

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