Refrigeration & Air-Conditioning Practice Set-4

Page 1 of 5

1. The advantage of dry compression is that

It permits complete evaporation in the evaporator

All of the above

It results in high volumetric and mechanical efficiency

It permits higher speeds to be used

2. 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)

(td₂ - td₃)/(td₃ - td₁)

(td₃ - td₂)/(td₃ - td₁)

(td₃ - td₁)/(td₃ - td₂)

3. 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

4. The superheating in a refrigeration cycle

Increases C.O.P.

Decreases C.O.P.

None of these

Does not alter C.O.P.

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

Carbon dioxide

Sulphur dioxide

R-12

Ammonia

6. Which of the following statement is correct?

The constant enthalpy lines are also constant wet bulb temperature lines

All of these

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

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

7. The sub-cooling in a refrigeration cycle

Decreases C.O.P.

None of these

Does not alter C.O.P.

Increases C.O.P.

8. Air conditioning means

Heating

Cooling

Dehumidifying

All of these

9. Vapour compression refrigeration is somewhat like

Carnot cycle

Reversed Carnot cycle

Rankine’s cycle

None of the above

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

26°C DBT and 60% RH

26°C DBT and 50% RH

20°C DBT and 50% RH

20°C DBT and 60% RH

Page 2 of 5

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

Indirect

Absorption

Compression

Direct

12. The Freon group of refrigerants are

Inorganic refrigerants

Zoetrope refrigerants

Halocarbon refrigerants

Hydrocarbon refrigerants

13. 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)]

None of these

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

0.622 Pv / (Pb - Pv)

14. The specific humidity during heating and humidification process.

Remains constant

None of these

Increases

Decreases

15. 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

16. 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 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

17. 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

18. The relative coefficient of performance is

Actual COP × theoretical COP

Actual COP/theoretical COP

Theoretical COP/actual COP

None of these

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

Compressor and evaporator

Compressor and condenser

Condenser and expansion valve

Expansion valve and evaporator

20. Superheating in a refrigeration cycle

Other factors decide C.O.P

Increases C.O.P

C.O.P remains unaltered

Decreases C.O.P

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21. During cooling and dehumidification, dry bulb temperature

Decreases

Increases

Remains constant

None of these

22. Air refrigeration operates on

Brayton cycle

Carnot cycle

Reversed Carnot cycle

Rankine’s cycle

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

High

Equal

Small

Anything

24. 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

25. 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)

26. Moisture in Freon refrigeration system causes

Freezing automatic regulating valve

Corrosion of whole system

High power consumption

Ineffective refrigeration

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

Specific

Absolute

None of these

Relative

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

Wet vapour

Saturated liquid

Dry saturated vapour

Superheated vapour

29. The specific humidity during dehumidification process

Increases

Decreases

None of these

Remains constant

30. The index which correlates the combined effects of air temperature, relative humidity and air velocity on the human body, is known as

Effective temperature

None of these

Dew point temperature

Mean radiant temperature

Page 4 of 5

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

Ammonia

Carbon dioxide

R-12

Sulphur dioxide

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

Soap and water

Halide torch

All of these

Sulphur sticks

33. Refrigeration in aeroplanes usually employs the following refrigerant

Freon-22

Air

Freon-11

CO2

34. 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

Will be lower

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

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

After passing through the expansion or throttle valve

Before entering the compressor

After passing through the condenser

Before passing through the condenser

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

Remain unaffected

Increase

Decrease

May increase or decrease depending on the type of refrigerant used

37. 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

0.2

6

1.2

5

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

DX coil

Flooded

None of these

Dry

39. During sensible cooling,

Partial pressure of vapour remains constant

Specific humidity increases

Wet bulb temperature increases

Relative humidity remains constant

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

Room latent heat load only

None of the above

Both room sensible heat and latent heat loads

Room sensible heat load only

Page 5 of 5

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

Lower than

Same as

Higher than

None of these

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

NH3

Freon-22

Freon-12

CO2

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

Solid and dry ice

Mixture of ice and water under equilibrium conditions

Ice at 4°C

Water at 0°C

44. 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

45. Ammonia absorption refrigeration cycle requires

Very little work input

Maximum work input

Nearly same work input as for vapour compression cycle

Zero work input

Refrigeration & Air-Conditioning Practice Set-4

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