Refrigeration & Air-Conditioning Practice Set-4

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

Saturated liquid

Wet vapour

Dry saturated vapour

Superheated vapour

2. The specific humidity during dehumidification process

None of these

Remains constant

Decreases

Increases

3. Air refrigeration operates on

Carnot cycle

Rankine’s cycle

Reversed Carnot cycle

Brayton cycle

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

Mixture of ice and water under equilibrium conditions

Ice at 4°C

Water at 0°C

Solid and dry ice

5. Moisture in Freon refrigeration system causes

Ineffective refrigeration

Corrosion of whole system

High power consumption

Freezing automatic regulating valve

6. 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

7. The superheating in a refrigeration cycle

Decreases C.O.P.

None of these

Increases C.O.P.

Does not alter C.O.P.

8. The relative coefficient of performance is

Theoretical COP/actual COP

None of these

Actual COP × theoretical COP

Actual COP/theoretical COP

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

More or less depending on ambient conditions

Less

More

Same

10. Which of the following statement is correct?

The constant enthalpy lines are also constant wet bulb temperature lines

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

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11. 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

12. The sub-cooling in a refrigeration cycle

None of these

Increases C.O.P.

Does not alter C.O.P.

Decreases C.O.P.

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

Direct

Absorption

Compression

Indirect

14. The Freon group of refrigerants are

Halocarbon refrigerants

Zoetrope refrigerants

Inorganic refrigerants

Hydrocarbon refrigerants

15. During sensible cooling,

Partial pressure of vapour remains constant

Specific humidity increases

Relative humidity remains constant

Wet bulb temperature increases

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

Relative

Specific

Absolute

None of these

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

High

Equal

Small

Anything

18. 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)

(td₂ - td₃)/(td₃ - td₁)

(td₃ - td₁)/(td₂ - td₃)

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

Ammonia

R-12

Carbon dioxide

Sulphur dioxide

20. 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

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21. Vapour compression refrigeration is somewhat like

Rankine’s cycle

None of the above

Reversed Carnot cycle

Carnot cycle

22. 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

23. 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 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

24. 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)]

0.622 Pv / (Pb - Pv)

None of these

μ/[1 - (1 - μ) (Ps/Pb)]

25. During cooling and dehumidification, dry bulb temperature

Decreases

None of these

Remains constant

Increases

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

All of the above

Enthalpy increase in compressor

Work done by compressor

Heat of compression

27. 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)

(h1 - h2)/ (hA - h2)

(hA - h1)/ (h2 - h1)

(h2 - hA)/ (h1 - h2)

(hA - h2)/ (h1 - h2)

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

Sulphur sticks

Soap and water

Halide torch

All of these

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

0.2

1.2

5

6

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

Freon-12

CO2

NH3

Freon-22

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

Evaporation of the refrigerant liquid

Condensation of the refrigerant vapour

Compression of the refrigerant vapour

Metering of the refrigerant liquid

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

Expansion valve and evaporator

Compressor and evaporator

Condenser and expansion valve

Compressor and condenser

33. Air conditioning means

All of these

Dehumidifying

Cooling

Heating

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

Sulphur dioxide

Carbon dioxide

R-12

Ammonia

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

Both room sensible heat and latent heat loads

None of the above

Room latent heat load only

Room sensible heat load only

36. 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 or equal to 3.65 kg

There is no such consideration

More than 10 kg

37. Superheating in a refrigeration cycle

Increases C.O.P

Decreases C.O.P

Other factors decide C.O.P

C.O.P remains unaltered

38. Ammonia absorption refrigeration cycle requires

Very little work input

Zero work input

Nearly same work input as for vapour compression cycle

Maximum work input

39. 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

40. 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

4 kW

1 kW

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41. Refrigeration in aeroplanes usually employs the following refrigerant

CO2

Freon-11

Freon-22

Air

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

Dry

DX coil

None of these

Flooded

43. The specific humidity during heating and humidification process.

Remains constant

Decreases

Increases

None of these

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

Same as

Higher than

Lower than

None of these

45. 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

Refrigeration & Air-Conditioning Practice Set-4

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