Refrigeration & Air-Conditioning Practice Set-4

Page 1 of 5

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

None of these

Same as

Higher than

Lower than

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

Small

Equal

Anything

High

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

Halide torch

Soap and water

All of these

Sulphur sticks

4. Air conditioning means

Heating

Cooling

All of these

Dehumidifying

5. The sub-cooling in a refrigeration cycle

None of these

Increases C.O.P.

Decreases C.O.P.

Does not alter C.O.P.

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

R-12

Ammonia

Carbon dioxide

Sulphur dioxide

7. The Freon group of refrigerants are

Hydrocarbon refrigerants

Halocarbon refrigerants

Zoetrope refrigerants

Inorganic refrigerants

8. Moisture in Freon refrigeration system causes

Corrosion of whole system

Ineffective refrigeration

High power consumption

Freezing automatic regulating valve

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

5

1.2

0.2

10. The relative coefficient of performance is

Actual COP/theoretical COP

Actual COP × theoretical COP

Theoretical COP/actual COP

None of these

Page 2 of 5

11. During cooling and dehumidification, dry bulb temperature

Increases

Remains constant

None of these

Decreases

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

Decrease

May increase or decrease depending on the type of refrigerant used

Remain unaffected

Increase

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

CO2

Freon-12

NH3

Freon-22

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

DX coil

Flooded

None of these

Dry

15. Superheating in a refrigeration cycle

Increases C.O.P

Other factors decide C.O.P

C.O.P remains unaltered

Decreases C.O.P

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

Saturated liquid

Dry saturated vapour

Superheated vapour

Wet vapour

17. Air refrigeration operates on

Reversed Carnot cycle

Rankine’s cycle

Brayton cycle

Carnot cycle

18. 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

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

More than or equal to 3.65 kg

There is no such consideration

Less than 2 kg

More than 10 kg

20. 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 - h2)/ (h1 - h2)

(hA - h1)/ (h2 - h1)

(h1 - h2)/ (hA - h2)

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21. During sensible cooling,

Relative humidity remains constant

Specific humidity increases

Wet bulb temperature increases

Partial pressure of vapour remains constant

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

Metering of the refrigerant liquid

Evaporation of the refrigerant liquid

Compression of the refrigerant vapour

Condensation of the refrigerant vapour

23. 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

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

None of these

Absolute

Relative

Specific

25. 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 - td₁)/(td₃ - td₂)

(td₃ - td₂)/(td₃ - td₁)

(td₃ - td₁)/(td₂ - td₃)

26. The specific humidity during heating and humidification process.

Increases

None of these

Decreases

Remains constant

27. Vapour compression refrigeration is somewhat like

Reversed Carnot cycle

Rankine’s cycle

Carnot cycle

None of the above

28. 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

Dew point temperature

Effective temperature

29. Refrigeration in aeroplanes usually employs the following refrigerant

CO2

Freon-22

Air

Freon-11

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

Ammonia

Carbon dioxide

R-12

Sulphur dioxide

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

After passing through the condenser

Before entering the compressor

After passing through the expansion or throttle valve

Before passing through the condenser

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

Compressor and evaporator

Condenser and expansion valve

Expansion valve and evaporator

Compressor and condenser

33. Which of the following statement is correct?

All of these

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

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

The constant enthalpy lines are also constant wet bulb temperature lines

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

Compression

Indirect

Direct

Absorption

35. 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)]

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

None of these

0.622 Pv / (Pb - Pv)

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

Water at 0°C

Ice at 4°C

Mixture of ice and water under equilibrium conditions

Solid and dry ice

37. 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 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

38. Ammonia absorption refrigeration cycle requires

Zero work input

Nearly same work input as for vapour compression cycle

Very little work input

Maximum work input

39. The specific humidity during dehumidification process

Decreases

Remains constant

None of these

Increases

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

None of the above

Room latent heat load only

Room sensible heat load only

Both room sensible heat and latent heat loads

Page 5 of 5

41. 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

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

2 kW

1 kW

4 kW

3 kW

43. The superheating in a refrigeration cycle

Does not alter C.O.P.

Decreases C.O.P.

None of these

Increases C.O.P.

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

Less

More or less depending on ambient conditions

More

Same

45. 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

Refrigeration & Air-Conditioning Practice Set-4

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