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

Superheated vapour

Dry saturated vapour

Wet vapour

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

None of these

Flooded

Dry

DX coil

3. 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

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

Remain unaffected

May increase or decrease depending on the type of refrigerant used

Decrease

Increase

5. Superheating in a refrigeration cycle

Other factors decide C.O.P

C.O.P remains unaltered

Increases C.O.P

Decreases C.O.P

6. During sensible cooling,

Specific humidity increases

Partial pressure of vapour remains constant

Relative humidity remains constant

Wet bulb temperature increases

7. The Freon group of refrigerants are

Hydrocarbon refrigerants

Inorganic refrigerants

Zoetrope refrigerants

Halocarbon refrigerants

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

Condensation of the refrigerant vapour

Compression of the refrigerant vapour

9. 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

1.2

5

0.2

10. The superheating in a refrigeration cycle

Increases C.O.P.

Decreases C.O.P.

None of these

Does not alter C.O.P.

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

NH3

Freon-22

CO2

Freon-12

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

Sulphur dioxide

R-12

Ammonia

Carbon dioxide

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

Water at 0°C

Solid and dry ice

Ice at 4°C

Mixture of ice and water under equilibrium conditions

14. 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)

μ/[1 - (1 - μ) (Ps/Pb)]

None of these

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

0.622 Pv / (Pb - Pv)

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

Room latent heat load only

None of the above

Both room sensible heat and latent heat loads

Room sensible heat load only

16. The specific humidity during dehumidification process

None of these

Remains constant

Decreases

Increases

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

Relative

Absolute

None of these

Specific

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

Ammonia

Sulphur dioxide

R-12

Carbon dioxide

19. Which of the following statement is correct?

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

All of these

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

The constant enthalpy lines are also constant wet bulb temperature lines

20. Air conditioning means

Dehumidifying

Cooling

Heating

All of these

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

Lower than

Higher than

Same as

None of these

22. The sub-cooling in a refrigeration cycle

Increases C.O.P.

Decreases C.O.P.

None of these

Does not alter C.O.P.

23. Air refrigeration operates on

Rankine’s cycle

Carnot cycle

Reversed Carnot cycle

Brayton cycle

24. Refrigeration in aeroplanes usually employs the following refrigerant

CO2

Air

Freon-11

Freon-22

25. 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

26. The relative coefficient of performance is

Actual COP/theoretical COP

Actual COP × theoretical COP

None of these

Theoretical COP/actual COP

27. During cooling and dehumidification, dry bulb temperature

Remains constant

None of these

Increases

Decreases

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

Expansion valve and evaporator

Compressor and evaporator

Condenser and expansion valve

Compressor and condenser

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

All of these

Halide torch

Sulphur sticks

Soap and water

30. 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

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31. Moisture in Freon refrigeration system causes

High power consumption

Corrosion of whole system

Freezing automatic regulating valve

Ineffective refrigeration

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

Direct

Indirect

Compression

Absorption

33. 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)

(td₂ - td₃)/(td₃ - td₁)

(td₃ - td₂)/(td₃ - td₁)

(td₃ - td₁)/(td₃ - td₂)

(td₃ - td₁)/(td₂ - td₃)

34. Vapour compression refrigeration is somewhat like

Rankine’s cycle

None of the above

Carnot cycle

Reversed Carnot cycle

35. 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

36. 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

37. 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

38. 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

Of adiabatic saturation of incoming stream

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

39. The specific humidity during heating and humidification process.

Remains constant

None of these

Decreases

Increases

40. 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)

(h2 - hA)/ (h1 - h2)

(hA - h1)/ (h2 - h1)

(h1 - h2)/ (hA - h2)

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

Equal

High

Small

Anything

42. 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

2 kW

1 kW

3 kW

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

After passing through the condenser

Before entering the compressor

Before passing through the condenser

After passing through the expansion or throttle valve

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

20°C DBT and 50% RH

20°C DBT and 60% RH

26°C DBT and 50% RH

26°C DBT and 60% RH

45. Ammonia absorption refrigeration cycle requires

Zero work input

Maximum work input

Nearly same work input as for vapour compression cycle

Very little work input

Refrigeration & Air-Conditioning Practice Set-4

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