Refrigeration & Air-Conditioning Practice Set-4

Page 1 of 5

1. The relative coefficient of performance is

Theoretical COP/actual COP

Actual COP × theoretical COP

None of these

Actual COP/theoretical COP

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

Superheated vapour

Wet vapour

Dry saturated vapour

Saturated liquid

3. 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

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

Will be higher

Will remain unaffected

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

Before passing through the condenser

After passing through the condenser

Before entering the compressor

After passing through the expansion or throttle valve

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

Indirect

Compression

Absorption

Direct

6. 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

7. 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 dry bulb and wet bulb temperatures of the incoming stream

Of adiabatic saturation of incoming stream

Which is lower than the dew point temperature of the incoming stream

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

8. 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

0.622 Pv / (Pb - Pv)

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

μ/[1 - (1 - μ) (Ps/Pb)]

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

Enthalpy increase in compressor

All of the above

Work done by compressor

Heat of compression

10. 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

4 kW

1 kW

2 kW

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

Same as

None of these

Lower than

Higher than

12. Which of the following statement is correct?

All of these

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

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

The constant enthalpy lines are also constant wet bulb temperature lines

13. The advantage of dry compression is that

It permits higher speeds to be used

It results in high volumetric and mechanical efficiency

It permits complete evaporation in the evaporator

All of the above

14. The Freon group of refrigerants are

Halocarbon refrigerants

Inorganic refrigerants

Zoetrope refrigerants

Hydrocarbon refrigerants

15. Refrigeration in aeroplanes usually employs the following refrigerant

Freon-22

CO2

Air

Freon-11

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

Equal

High

Small

Anything

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

Halide torch

Sulphur sticks

All of these

Soap and water

18. 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

19. The specific humidity during dehumidification process

Remains constant

Decreases

None of these

Increases

20. 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

Mean radiant temperature

Effective temperature

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21. Superheating in a refrigeration cycle

C.O.P remains unaltered

Other factors decide C.O.P

Decreases C.O.P

Increases C.O.P

22. 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

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

None of these

DX coil

Flooded

Dry

24. Ammonia absorption refrigeration cycle requires

Zero work input

Very little work input

Nearly same work input as for vapour compression cycle

Maximum work input

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

Ice at 4°C

Water at 0°C

Solid and dry ice

Mixture of ice and water under equilibrium conditions

26. Moisture in Freon refrigeration system causes

High power consumption

Corrosion of whole system

Ineffective refrigeration

Freezing automatic regulating valve

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

Ammonia

Carbon dioxide

Sulphur dioxide

R-12

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

There is no such consideration

Less than 2 kg

More than or equal to 3.65 kg

More than 10 kg

29. 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

5

6

0.2

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

More or less depending on ambient conditions

More

Less

Same

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

Sulphur dioxide

Ammonia

R-12

Carbon dioxide

32. Air refrigeration operates on

Brayton cycle

Reversed Carnot cycle

Rankine’s cycle

Carnot cycle

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

Compressor and condenser

Expansion valve and evaporator

Condenser and expansion valve

Compressor and evaporator

34. During cooling and dehumidification, dry bulb temperature

Increases

Remains constant

Decreases

None of these

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

20°C DBT and 50% RH

26°C DBT and 60% RH

20°C DBT and 60% RH

26°C DBT and 50% RH

36. 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 - h1)/ (h2 - h1)

(hA - h2)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

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

Absolute

None of these

Specific

Relative

38. The superheating in a refrigeration cycle

Increases C.O.P.

Does not alter C.O.P.

Decreases C.O.P.

None of these

39. 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)/(td₃ - td₂)

(td₃ - td₁)/(td₂ - td₃)

(td₂ - td₃)/(td₃ - td₁)

(td₃ - td₂)/(td₃ - td₁)

40. Air conditioning means

All of these

Dehumidifying

Cooling

Heating

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41. The specific humidity during heating and humidification process.

Increases

None of these

Remains constant

Decreases

42. Vapour compression refrigeration is somewhat like

Reversed Carnot cycle

None of the above

Carnot cycle

Rankine’s cycle

43. The sub-cooling in a refrigeration cycle

None of these

Increases C.O.P.

Does not alter C.O.P.

Decreases C.O.P.

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

NH3

Freon-22

CO2

Freon-12

45. During sensible cooling,

Specific humidity increases

Relative humidity remains constant

Wet bulb temperature increases

Partial pressure of vapour remains constant

Refrigeration & Air-Conditioning Practice Set-4

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