Refrigeration & Air-Conditioning Practice Set-4

Page 1 of 5

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

Soap and water

Sulphur sticks

All of these

Halide torch

2. The superheating in a refrigeration cycle

None of these

Decreases C.O.P.

Increases C.O.P.

Does not alter C.O.P.

3. Air refrigeration operates on

Rankine’s cycle

Carnot cycle

Reversed Carnot cycle

Brayton cycle

4. The specific humidity during dehumidification process

Decreases

Remains constant

None of these

Increases

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

More

More or less depending on ambient conditions

Same

Less

6. The sub-cooling in a refrigeration cycle

Increases C.O.P.

None of these

Does not alter C.O.P.

Decreases C.O.P.

7. During sensible cooling,

Partial pressure of vapour remains constant

Relative humidity remains constant

Specific humidity increases

Wet bulb temperature increases

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

Absolute

Relative

Specific

None of these

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

Work done by compressor

All of the above

Heat of compression

Enthalpy increase in compressor

10. 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)

(h2 - hA)/ (h1 - h2)

(hA - h2)/ (h1 - h2)

(hA - h1)/ (h2 - h1)

Page 2 of 5

11. 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

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

Compressor and condenser

Compressor and evaporator

Condenser and expansion valve

Expansion valve and evaporator

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

There is no such consideration

More than or equal to 3.65 kg

More than 10 kg

Less than 2 kg

14. Ammonia absorption refrigeration cycle requires

Maximum work input

Zero work input

Nearly same work input as for vapour compression cycle

Very little work input

15. The specific humidity during heating and humidification process.

Remains constant

Decreases

Increases

None of these

16. Air conditioning means

Cooling

All of these

Dehumidifying

Heating

17. 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 be lower

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

Will remain unaffected

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

Solid and dry ice

Water at 0°C

Ice at 4°C

Mixture of ice and water under equilibrium conditions

19. 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

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

Flooded

Dry

DX coil

None of these

Page 3 of 5

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

After passing through the expansion or throttle valve

After passing through the condenser

Before entering the compressor

Before passing through the condenser

22. 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

3 kW

2 kW

1 kW

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

Equal

Small

Anything

High

24. Refrigeration in aeroplanes usually employs the following refrigerant

Freon-11

Air

CO2

Freon-22

25. Superheating in a refrigeration cycle

Decreases C.O.P

Increases C.O.P

Other factors decide C.O.P

C.O.P remains unaltered

26. Which of the following statement is correct?

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

The constant enthalpy lines are also constant wet bulb temperature lines

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

All of these

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

Saturated liquid

Superheated vapour

Dry saturated vapour

Wet vapour

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

Indirect

Direct

Absorption

Compression

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

None of these

Same as

Higher than

Lower than

30. 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

Page 4 of 5

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

20°C DBT and 50% RH

26°C DBT and 50% RH

20°C DBT and 60% RH

26°C DBT and 60% RH

32. Vapour compression refrigeration is somewhat like

None of the above

Rankine’s cycle

Carnot cycle

Reversed Carnot cycle

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

CO2

NH3

Freon-22

Freon-12

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

Carbon dioxide

R-12

Ammonia

Sulphur dioxide

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

Sulphur dioxide

R-12

Ammonia

Carbon dioxide

36. During cooling and dehumidification, dry bulb temperature

Increases

Remains constant

Decreases

None of these

37. The Freon group of refrigerants are

Hydrocarbon refrigerants

Inorganic refrigerants

Halocarbon refrigerants

Zoetrope refrigerants

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

None of the above

Room sensible heat load only

Room latent heat load only

Both room sensible heat and latent heat loads

39. The relative coefficient of performance is

None of these

Actual COP/theoretical COP

Theoretical COP/actual COP

Actual COP × theoretical COP

40. 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)

Page 5 of 5

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

Compression of the refrigerant vapour

Metering of the refrigerant liquid

Condensation of the refrigerant vapour

Evaporation of the refrigerant liquid

42. Moisture in Freon refrigeration system causes

Ineffective refrigeration

High power consumption

Freezing automatic regulating valve

Corrosion of whole system

43. 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)

μ/[1 - (1 - μ) (Ps/Pb)]

None of these

44. 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

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

Of adiabatic saturation of incoming stream

45. 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

Increase

Decrease

Remain unaffected

Refrigeration & Air-Conditioning Practice Set-4

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