Refrigeration & Air-Conditioning Practice Set-4

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1. The specific humidity during dehumidification process

Increases

None of these

Decreases

Remains constant

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

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

Which lies between the wet bulb and dew point temperatures of the incoming stream

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

Mixture of ice and water under equilibrium conditions

Water at 0°C

Ice at 4°C

Solid and dry ice

4. 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)

None of these

0.622 Pv / (Pb - Pv)

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

μ/[1 - (1 - μ) (Ps/Pb)]

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

None of these

Flooded

DX coil

Dry

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

After passing through the condenser

Before passing through the condenser

After passing through the expansion or throttle valve

Before entering the compressor

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

Sulphur sticks

Soap and water

Halide torch

All of these

8. Ammonia absorption refrigeration cycle requires

Very little work input

Zero work input

Maximum work input

Nearly same work input as for vapour compression cycle

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

More

Less

More or less depending on ambient conditions

Same

10. The superheating in a refrigeration cycle

Does not alter C.O.P.

Decreases C.O.P.

None of these

Increases C.O.P.

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11. The specific humidity during heating and humidification process.

Remains constant

Increases

None of these

Decreases

12. Superheating in a refrigeration cycle

Decreases C.O.P

Increases C.O.P

C.O.P remains unaltered

Other factors decide C.O.P

13. 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

Dew point temperature

None of these

14. Refrigeration in aeroplanes usually employs the following refrigerant

Freon-22

Air

CO2

Freon-11

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

Carbon dioxide

Sulphur dioxide

R-12

Ammonia

16. The advantage of dry compression is that

It results in high volumetric and mechanical efficiency

All of the above

It permits higher speeds to be used

It permits complete evaporation in the evaporator

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

Increase

Decrease

Remain unaffected

May increase or decrease depending on the type of refrigerant used

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

Compressor and evaporator

Condenser and expansion valve

Expansion valve and evaporator

Compressor and condenser

19. Which of the following statement is correct?

All of these

The constant enthalpy lines are also constant wet bulb temperature lines

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

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

20. Air refrigeration operates on

Carnot cycle

Brayton cycle

Reversed Carnot cycle

Rankine’s cycle

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21. 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 - h1)/ (h2 - h1)

(hA - h2)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

22. 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 lower

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

Will be higher

Will remain unaffected

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

Specific

Absolute

Relative

None of these

24. During cooling and dehumidification, dry bulb temperature

None of these

Decreases

Increases

Remains constant

25. Vapour compression refrigeration is somewhat like

None of the above

Rankine’s cycle

Reversed Carnot cycle

Carnot cycle

26. The sub-cooling in a refrigeration cycle

None of these

Decreases C.O.P.

Does not alter C.O.P.

Increases C.O.P.

27. 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 10 kg

Less than 2 kg

More than or equal to 3.65 kg

28. During sensible cooling,

Specific humidity increases

Relative humidity remains constant

Partial pressure of vapour remains constant

Wet bulb temperature increases

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

26°C DBT and 50% RH

20°C DBT and 50% RH

26°C DBT and 60% RH

20°C DBT and 60% RH

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

Higher than

None of these

Same as

Lower than

Page 4 of 5

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

Both room sensible heat and latent heat loads

Room latent heat load only

Room sensible heat load only

None of the above

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

Compression of the refrigerant vapour

Evaporation of the refrigerant liquid

Condensation of the refrigerant vapour

Metering of the refrigerant liquid

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

Compression

Direct

Indirect

Absorption

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

Wet vapour

Saturated liquid

Superheated vapour

Dry saturated vapour

35. Moisture in Freon refrigeration system causes

Ineffective refrigeration

Freezing automatic regulating valve

Corrosion of whole system

High power consumption

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

CO2

NH3

Freon-12

Freon-22

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

High

Small

Equal

Anything

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

Heat of compression

Enthalpy increase in compressor

Work done by compressor

All of the above

39. The Freon group of refrigerants are

Halocarbon refrigerants

Zoetrope refrigerants

Inorganic refrigerants

Hydrocarbon refrigerants

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

4 kW

1 kW

3 kW

2 kW

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41. The relative coefficient of performance is

Theoretical COP/actual COP

Actual COP/theoretical COP

None of these

Actual COP × theoretical COP

42. Air conditioning means

Cooling

Dehumidifying

Heating

All of these

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

Ammonia

Sulphur dioxide

R-12

Carbon dioxide

44. 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)

45. 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

6

5

Refrigeration & Air-Conditioning Practice Set-4

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