Refrigeration & Air-Conditioning Practice Set-4

Page 1 of 5

1. 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

2. The advantage of dry compression is that

It permits complete evaporation in the evaporator

It permits higher speeds to be used

It results in high volumetric and mechanical efficiency

All of the above

3. 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 - h1)/ (h2 - h1)

(hA - h2)/ (h1 - h2)

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

NH3

Freon-12

Freon-22

CO2

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

26°C DBT and 60% RH

20°C DBT and 50% RH

26°C DBT and 50% RH

20°C DBT and 60% RH

6. Vapour compression refrigeration is somewhat like

Carnot cycle

Rankine’s cycle

Reversed Carnot cycle

None of the above

7. 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

Of adiabatic saturation of 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

8. 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

9. 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

Remain unaffected

Increase

Decrease

10. Superheating in a refrigeration cycle

Decreases C.O.P

Increases C.O.P

Other factors decide C.O.P

C.O.P remains unaltered

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11. 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

There is no such consideration

More than 10 kg

12. 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

2 kW

4 kW

3 kW

1 kW

13. The sub-cooling in a refrigeration cycle

Does not alter C.O.P.

Decreases C.O.P.

Increases C.O.P.

None of these

14. 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

15. 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

μ/[1 - (1 - μ) (Ps/Pb)]

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

0.622 Pv / (Pb - Pv)

16. The superheating in a refrigeration cycle

Increases C.O.P.

None of these

Decreases C.O.P.

Does not alter C.O.P.

17. The Freon group of refrigerants are

Inorganic refrigerants

Halocarbon refrigerants

Hydrocarbon refrigerants

Zoetrope refrigerants

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

Saturated liquid

Dry saturated vapour

Superheated vapour

Wet vapour

19. The specific humidity during heating and humidification process.

Decreases

Increases

None of these

Remains constant

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

Flooded

None of these

DX coil

Dry

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

R-12

Ammonia

Carbon dioxide

Sulphur dioxide

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

Less

More

Same

More or less depending on ambient conditions

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

Solid and dry ice

Water at 0°C

Mixture of ice and water under equilibrium conditions

Ice at 4°C

24. The relative coefficient of performance is

Actual COP × theoretical COP

Theoretical COP/actual COP

Actual COP/theoretical COP

None of these

25. 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

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

Will be lower

Will remain unaffected

26. 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

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

Carbon dioxide

Sulphur dioxide

R-12

Ammonia

28. Refrigeration in aeroplanes usually employs the following refrigerant

Freon-22

CO2

Air

Freon-11

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

Indirect

Absorption

Direct

Compression

30. During cooling and dehumidification, dry bulb temperature

Remains constant

Decreases

Increases

None of these

Page 4 of 5

31. Ammonia absorption refrigeration cycle requires

Very little work input

Maximum work input

Zero work input

Nearly same work input as for vapour compression cycle

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

Small

Equal

Anything

High

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

None of these

Lower than

Higher than

Same as

34. Air refrigeration operates on

Reversed Carnot cycle

Rankine’s cycle

Brayton cycle

Carnot cycle

35. Air conditioning means

Cooling

All of these

Dehumidifying

Heating

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

Condenser and expansion valve

Compressor and evaporator

Compressor and condenser

Expansion valve and evaporator

37. The specific humidity during dehumidification process

None of these

Decreases

Increases

Remains constant

38. Moisture in Freon refrigeration system causes

High power consumption

Corrosion of whole system

Freezing automatic regulating valve

Ineffective refrigeration

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

Absolute

None of these

Relative

Specific

40. Which of the following statement is correct?

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

All of these

The constant enthalpy lines are also constant wet bulb temperature lines

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

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41. 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

None of the above

Room sensible heat load only

42. During sensible cooling,

Wet bulb temperature increases

Partial pressure of vapour remains constant

Specific humidity increases

Relative humidity remains constant

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

Effective temperature

Mean radiant temperature

None of these

Dew point temperature

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

All of these

Sulphur sticks

Halide torch

Soap and water

45. 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)/(td₃ - td₂)

(td₃ - td₂)/(td₃ - td₁)

(td₃ - td₁)/(td₂ - td₃)

(td₂ - td₃)/(td₃ - td₁)

Refrigeration & Air-Conditioning Practice Set-4

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