Refrigeration & Air-Conditioning Practice Set-4

Page 1 of 5

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

Sulphur sticks

Halide torch

Soap and water

All of these

2. 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

0.2

5

6

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

Compressor and evaporator

Condenser and expansion valve

Expansion valve and evaporator

Compressor and condenser

4. 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

5. 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)]

μ/[1 - (1 - μ) (Ps/Pb)]

None of these

0.622 Pv / (Pb - Pv)

6. During sensible cooling,

Relative humidity remains constant

Specific humidity increases

Partial pressure of vapour remains constant

Wet bulb temperature increases

7. Air refrigeration operates on

Reversed Carnot cycle

Carnot cycle

Rankine’s cycle

Brayton cycle

8. Vapour compression refrigeration is somewhat like

None of the above

Carnot cycle

Reversed Carnot cycle

Rankine’s cycle

9. 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 - h2)/ (h1 - h2)

(h2 - hA)/ (h1 - h2)

(hA - h1)/ (h2 - h1)

10. 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

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11. In order to cool and dehumidify a stream of moist air, it must be passed over the coil at a temperature

Of adiabatic saturation of incoming stream

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

12. 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

13. Air conditioning means

Cooling

Dehumidifying

Heating

All of these

14. The sub-cooling in a refrigeration cycle

Does not alter C.O.P.

None of these

Increases C.O.P.

Decreases C.O.P.

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

Increase

May increase or decrease depending on the type of refrigerant used

Decrease

Remain unaffected

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

Carbon dioxide

Sulphur dioxide

R-12

Ammonia

17. The Freon group of refrigerants are

Inorganic refrigerants

Halocarbon refrigerants

Zoetrope refrigerants

Hydrocarbon refrigerants

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

High

Small

Anything

Equal

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

Mixture of ice and water under equilibrium conditions

Solid and dry ice

Water at 0°C

Ice at 4°C

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

Compression

Indirect

Absorption

Direct

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21. The relative coefficient of performance is

Theoretical COP/actual COP

Actual COP × theoretical COP

Actual COP/theoretical COP

None of these

22. Ammonia absorption refrigeration cycle requires

Zero work input

Maximum work input

Very little work input

Nearly same work input as for vapour compression cycle

23. 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)/(td₂ - td₃)

(td₃ - td₁)/(td₃ - td₂)

(td₂ - td₃)/(td₃ - td₁)

(td₃ - td₂)/(td₃ - td₁)

24. Refrigeration in aeroplanes usually employs the following refrigerant

Freon-11

CO2

Freon-22

Air

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

Wet vapour

Superheated vapour

Dry saturated vapour

Saturated liquid

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

CO2

NH3

Freon-12

Freon-22

27. 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

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

More

Same

Less

More or less depending on ambient conditions

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

DX coil

Flooded

Dry

None of these

30. 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

More than 10 kg

There is no such consideration

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31. The specific humidity during heating and humidification process.

Remains constant

Decreases

None of these

Increases

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

None of the above

Both room sensible heat and latent heat loads

Room latent heat load only

Room sensible heat load only

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

Evaporation of the refrigerant liquid

Condensation of the refrigerant vapour

Metering of the refrigerant liquid

Compression of the refrigerant vapour

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

Lower than

None of these

Same as

Higher than

35. Moisture in Freon refrigeration system causes

Ineffective refrigeration

Corrosion of whole system

Freezing automatic regulating valve

High power consumption

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

R-12

Sulphur dioxide

Ammonia

Carbon dioxide

37. The superheating in a refrigeration cycle

None of these

Decreases C.O.P.

Increases C.O.P.

Does not alter C.O.P.

38. 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

1 kW

3 kW

2 kW

4 kW

39. The specific humidity during dehumidification process

Increases

Remains constant

None of these

Decreases

40. During cooling and dehumidification, dry bulb temperature

None of these

Remains constant

Decreases

Increases

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41. Superheating in a refrigeration cycle

C.O.P remains unaltered

Decreases C.O.P

Increases C.O.P

Other factors decide C.O.P

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

Relative

Specific

None of these

Absolute

43. Which of the following statement is correct?

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

All of these

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

Before passing through the condenser

After passing through the expansion or throttle valve

Before entering the compressor

After passing through the condenser

45. The advantage of dry compression is that

It results in high volumetric and mechanical efficiency

All of the above

It permits complete evaporation in the evaporator

It permits higher speeds to be used

Refrigeration & Air-Conditioning Practice Set-4

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