Refrigeration & Air-Conditioning Practice Set-4

Page 1 of 5

1. During cooling and dehumidification, dry bulb temperature

Decreases

Increases

Remains constant

None of these

2. The advantage of dry compression is that

It permits higher speeds to be used

It results in high volumetric and mechanical efficiency

All of the above

It permits complete evaporation in the evaporator

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

Same

More or less depending on ambient conditions

Less

More

4. The specific humidity during heating and humidification process.

Increases

Decreases

None of these

Remains constant

5. 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

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

Of adiabatic saturation of incoming stream

6. The sub-cooling in a refrigeration cycle

None of these

Increases C.O.P.

Decreases C.O.P.

Does not alter C.O.P.

7. 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

2 kW

3 kW

8. The Freon group of refrigerants are

Halocarbon refrigerants

Hydrocarbon refrigerants

Inorganic refrigerants

Zoetrope refrigerants

9. 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)

0.622 Pv / (Pb - Pv)

μ/[1 - (1 - μ) (Ps/Pb)]

None of these

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

10. The superheating in a refrigeration cycle

Decreases C.O.P.

Does not alter C.O.P.

Increases C.O.P.

None of these

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11. 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

More than 10 kg

Less than 2 kg

There is no such consideration

12. Which of the following statement is correct?

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

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

The constant enthalpy lines are also constant wet bulb temperature lines

All of these

13. 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

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

Solid and dry ice

Mixture of ice and water under equilibrium conditions

Water at 0°C

Ice at 4°C

15. 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 - h1)/ (h2 - h1)

(h1 - h2)/ (hA - h2)

(hA - h2)/ (h1 - h2)

(h2 - hA)/ (h1 - h2)

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

Expansion valve and evaporator

Condenser and expansion valve

Compressor and condenser

Compressor and evaporator

17. 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 passing through the condenser

Before entering the compressor

18. 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 - td₂)/(td₃ - td₁)

(td₂ - td₃)/(td₃ - td₁)

(td₃ - td₁)/(td₃ - td₂)

19. 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

None of these

Dew point temperature

Effective temperature

20. 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

Page 3 of 5

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

None of these

Lower than

Higher than

Same as

22. Superheating in a refrigeration cycle

C.O.P remains unaltered

Other factors decide C.O.P

Increases C.O.P

Decreases C.O.P

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

Specific

None of these

Relative

Absolute

24. Air conditioning means

Heating

All of these

Cooling

Dehumidifying

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

All of these

Halide torch

Sulphur sticks

Soap and water

26. The relative coefficient of performance is

None of these

Actual COP/theoretical COP

Theoretical COP/actual COP

Actual COP × theoretical COP

27. Moisture in Freon refrigeration system causes

Freezing automatic regulating valve

Ineffective refrigeration

High power consumption

Corrosion of whole system

28. 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

5

0.2

6

1.2

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

Dry

None of these

DX coil

Flooded

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

Room latent heat load only

Both room sensible heat and latent heat loads

Room sensible heat load only

None of the above

Page 4 of 5

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

Superheated vapour

Wet vapour

Saturated liquid

Dry saturated vapour

32. 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

Increase

Remain unaffected

33. Air refrigeration operates on

Reversed Carnot cycle

Brayton cycle

Rankine’s cycle

Carnot cycle

34. Vapour compression refrigeration is somewhat like

None of the above

Carnot cycle

Reversed Carnot cycle

Rankine’s cycle

35. 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 lower

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

Will be higher

36. The specific humidity during dehumidification process

None of these

Remains constant

Increases

Decreases

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

Small

Equal

Anything

High

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

Direct

Compression

Indirect

Absorption

39. During sensible cooling,

Wet bulb temperature increases

Partial pressure of vapour remains constant

Relative humidity remains constant

Specific humidity increases

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

Carbon dioxide

R-12

Ammonia

Sulphur dioxide

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41. Refrigeration in aeroplanes usually employs the following refrigerant

Air

Freon-22

CO2

Freon-11

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

20°C DBT and 60% RH

26°C DBT and 50% RH

20°C DBT and 50% RH

26°C DBT and 60% RH

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

R-12

Sulphur dioxide

Carbon dioxide

Ammonia

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

Freon-12

Freon-22

NH3

CO2

45. Ammonia absorption refrigeration cycle requires

Maximum work input

Nearly same work input as for vapour compression cycle

Very little work input

Zero work input

Refrigeration & Air-Conditioning Practice Set-4

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