Refrigeration & Air-Conditioning Practice Set-4

June 7, 2021

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Page 1 of 5

1. The superheating in a refrigeration cycle

Decreases C.O.P.

None of these

Does not alter C.O.P.

Increases C.O.P.

2. The Freon group of refrigerants are

Inorganic refrigerants

Zoetrope refrigerants

Halocarbon refrigerants

Hydrocarbon refrigerants

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

DX coil

Flooded

Dry

None of these

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

Compressor and condenser

Condenser and expansion valve

Expansion valve and evaporator

Compressor and evaporator

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

20°C DBT and 60% RH

20°C DBT and 50% RH

26°C DBT and 60% RH

26°C DBT and 50% RH

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

Relative

Specific

Absolute

None of these

7. 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

All of these

The constant enthalpy lines are also constant wet bulb temperature lines

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

Before entering the compressor

Before passing through the condenser

After passing through the condenser

After passing through the expansion or throttle valve

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

More or less depending on ambient conditions

Same

Less

10. The advantage of dry compression is that

It results in high volumetric and mechanical efficiency

It permits higher speeds to be used

All of the above

It permits complete evaporation in the evaporator

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

Heat of compression

All of the above

Work done by compressor

Enthalpy increase in compressor

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

CO2

NH3

Freon-22

Freon-12

13. Vapour compression refrigeration is somewhat like

None of the above

Reversed Carnot cycle

Rankine’s cycle

Carnot cycle

14. 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

2 kW

3 kW

1 kW

15. Superheating in a refrigeration cycle

Other factors decide C.O.P

Increases C.O.P

C.O.P remains unaltered

Decreases C.O.P

16. Refrigeration in aeroplanes usually employs the following refrigerant

Freon-22

Air

CO2

Freon-11

17. 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

Increase

Decrease

Remain unaffected

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

Small

High

Equal

Anything

19. The specific humidity during heating and humidification process.

Remains constant

Decreases

Increases

None of these

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

Higher than

None of these

Lower than

Same as

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21. 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

1.2

22. The sub-cooling in a refrigeration cycle

Does not alter C.O.P.

None of these

Increases C.O.P.

Decreases C.O.P.

23. Air refrigeration operates on

Rankine’s cycle

Reversed Carnot cycle

Carnot cycle

Brayton cycle

24. During cooling and dehumidification, dry bulb temperature

Increases

Remains constant

None of these

Decreases

25. During sensible cooling,

Wet bulb temperature increases

Specific humidity increases

Relative humidity remains constant

Partial pressure of vapour remains constant

26. 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

More than or equal to 3.65 kg

Less than 2 kg

27. The specific humidity during dehumidification process

Decreases

Increases

Remains constant

None of these

28. 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)

(h1 - h2)/ (hA - h2)

(hA - h2)/ (h1 - h2)

29. Moisture in Freon refrigeration system causes

Corrosion of whole system

Freezing automatic regulating valve

High power consumption

Ineffective refrigeration

30. 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 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

Which lies between the dry bulb and wet bulb temperatures of the incoming stream

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

Metering of the refrigerant liquid

Condensation of the refrigerant vapour

Compression of the refrigerant vapour

Evaporation of the refrigerant liquid

32. 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

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

μ/[1 - (1 - μ) (Ps/Pb)]

0.622 Pv / (Pb - Pv)

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

Compression

Absorption

Direct

Indirect

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

Sulphur sticks

Soap and water

All of these

Halide torch

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

Both room sensible heat and latent heat loads

Room sensible heat load only

None of the above

Room latent heat load only

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

Dew point temperature

None of these

Mean radiant temperature

Effective temperature

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

Mixture of ice and water under equilibrium conditions

Water at 0°C

Solid and dry ice

Ice at 4°C

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

R-12

Sulphur dioxide

Carbon dioxide

Ammonia

39. 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)

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

Saturated liquid

Dry saturated vapour

Wet vapour

Superheated vapour

Page 5 of 5

41. Ammonia absorption refrigeration cycle requires

Zero work input

Very little work input

Maximum work input

Nearly same work input as for vapour compression cycle

42. 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

Will be lower

Will remain unaffected

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

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

Sulphur dioxide

Carbon dioxide

R-12

Ammonia

44. Air conditioning means

Cooling

Dehumidifying

All of these

Heating

45. The relative coefficient of performance is

Actual COP/theoretical COP

Actual COP × theoretical COP

None of these

Theoretical COP/actual COP

Refrigeration & Air-Conditioning Practice Set-4

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