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 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

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

All of the above

Heat of compression

Work done by compressor

Enthalpy increase in compressor

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

Compressor and condenser

Compressor and evaporator

Condenser and expansion valve

Expansion valve and evaporator

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

6

0.2

5

1.2

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

Ice at 4°C

Mixture of ice and water under equilibrium conditions

Solid and dry ice

Water at 0°C

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

Dry saturated vapour

Saturated liquid

Wet vapour

Superheated vapour

7. During sensible cooling,

Partial pressure of vapour remains constant

Wet bulb temperature increases

Specific humidity increases

Relative humidity remains constant

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

Evaporation of the refrigerant liquid

Metering of the refrigerant liquid

Compression of the refrigerant vapour

Condensation of the refrigerant vapour

9. The specific humidity during heating and humidification process.

None of these

Remains constant

Decreases

Increases

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

Flooded

None of these

DX coil

Dry

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11. Moisture in Freon refrigeration system causes

Ineffective refrigeration

Corrosion of whole system

High power consumption

Freezing automatic regulating valve

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

20°C DBT and 50% RH

26°C DBT and 60% RH

26°C DBT and 50% RH

20°C DBT and 60% RH

13. 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

Will remain unaffected

Will be lower

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

14. 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

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

Carbon dioxide

Ammonia

Sulphur dioxide

R-12

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

Higher than

Lower than

Same as

None of these

17. The relative coefficient of performance is

Actual COP/theoretical COP

None of these

Actual COP × theoretical COP

Theoretical COP/actual COP

18. 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

Remain unaffected

Increase

Decrease

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

1 kW

4 kW

20. The advantage of dry compression is that

All of the above

It permits higher speeds to be used

It results in high volumetric and mechanical efficiency

It permits complete evaporation in the evaporator

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21. Ammonia absorption refrigeration cycle requires

Nearly same work input as for vapour compression cycle

Very little work input

Maximum work input

Zero work input

22. Vapour compression refrigeration is somewhat like

None of the above

Rankine’s cycle

Reversed Carnot cycle

Carnot cycle

23. The superheating in a refrigeration cycle

Increases C.O.P.

Does not alter C.O.P.

Decreases C.O.P.

None of these

24. 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

Mean radiant temperature

Effective temperature

Dew point temperature

25. The sub-cooling in a refrigeration cycle

None of these

Increases C.O.P.

Decreases C.O.P.

Does not alter C.O.P.

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

Small

Equal

Anything

High

27. 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)

(td₂ - td₃)/(td₃ - td₁)

(td₃ - td₁)/(td₂ - td₃)

(td₃ - td₁)/(td₃ - td₂)

28. 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

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

0.622 Pv / (Pb - Pv)

μ/[1 - (1 - μ) (Ps/Pb)]

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

Ammonia

Sulphur dioxide

Carbon dioxide

R-12

30. 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)

(hA - h1)/ (h2 - h1)

(h2 - hA)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

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

Halide torch

All of these

Soap and water

Sulphur sticks

32. Air conditioning means

All of these

Dehumidifying

Cooling

Heating

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

None of these

Relative

Specific

Absolute

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

More than 10 kg

More than or equal to 3.65 kg

There is no such consideration

Less than 2 kg

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

Absorption

Direct

Compression

Indirect

36. During cooling and dehumidification, dry bulb temperature

Increases

Remains constant

None of these

Decreases

37. The Freon group of refrigerants are

Inorganic refrigerants

Zoetrope refrigerants

Halocarbon refrigerants

Hydrocarbon refrigerants

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

Same

Less

More or less depending on ambient conditions

More

39. Refrigeration in aeroplanes usually employs the following refrigerant

Air

Freon-22

Freon-11

CO2

40. Superheating in a refrigeration cycle

Other factors decide C.O.P

C.O.P remains unaltered

Decreases C.O.P

Increases C.O.P

Page 5 of 5

41. Air refrigeration operates on

Carnot cycle

Reversed Carnot cycle

Rankine’s cycle

Brayton cycle

42. 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

Of adiabatic saturation of incoming stream

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

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

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

CO2

NH3

Freon-22

Freon-12

44. The specific humidity during dehumidification process

None of these

Remains constant

Increases

Decreases

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

Before entering the compressor

After passing through the expansion or throttle valve

After passing through the condenser

Before passing through the condenser

Refrigeration & Air-Conditioning Practice Set-4

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