Refrigeration & Air-Conditioning Practice Set-4

June 7, 2021

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1. The Freon group of refrigerants are

Inorganic refrigerants

Halocarbon refrigerants

Zoetrope refrigerants

Hydrocarbon refrigerants

2. Air refrigeration operates on

Reversed Carnot cycle

Brayton cycle

Rankine’s cycle

Carnot cycle

3. 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

0.622 Pv / (Pb - Pv)

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

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

Equal

Small

Anything

High

5. Air conditioning means

Heating

Cooling

Dehumidifying

All of these

6. 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

1 kW

4 kW

3 kW

7. 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

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

26°C DBT and 50% RH

20°C DBT and 50% RH

20°C DBT and 60% RH

26°C DBT and 60% RH

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

Enthalpy increase in compressor

Work done by compressor

All of the above

Heat of compression

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

Less

More or less depending on ambient conditions

Same

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11. 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)

12. 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

Dew point temperature

Effective temperature

None of these

13. During sensible cooling,

Specific humidity increases

Wet bulb temperature increases

Partial pressure of vapour remains constant

Relative humidity remains constant

14. 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

There is no such consideration

Less than 2 kg

15. The advantage of dry compression is that

It results in high volumetric and mechanical efficiency

It permits complete evaporation in the evaporator

All of the above

It permits higher speeds to be used

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

Water at 0°C

Ice at 4°C

Mixture of ice and water under equilibrium conditions

Solid and dry ice

17. 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 remain unaffected

Will be lower

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

18. Which of the following statement is correct?

The constant enthalpy lines are also constant wet bulb temperature lines

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

All of these

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

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

R-12

Carbon dioxide

Sulphur dioxide

Ammonia

20. 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

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21. During cooling and dehumidification, dry bulb temperature

Remains constant

None of these

Decreases

Increases

22. The specific humidity during heating and humidification process.

Decreases

None of these

Remains constant

Increases

23. Ammonia absorption refrigeration cycle requires

Zero work input

Nearly same work input as for vapour compression cycle

Very little work input

Maximum work input

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

Lower than

Higher than

Same as

None of these

25. Superheating in a refrigeration cycle

Other factors decide C.O.P

Decreases C.O.P

C.O.P remains unaltered

Increases C.O.P

26. 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

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

Dry

Flooded

None of these

DX coil

28. Vapour compression refrigeration is somewhat like

Rankine’s cycle

Carnot cycle

Reversed Carnot cycle

None of the above

29. 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

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

Evaporation of the refrigerant liquid

Condensation of the refrigerant vapour

Metering of the refrigerant liquid

Compression of the refrigerant vapour

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31. The relative coefficient of performance is

Actual COP × theoretical COP

None of these

Actual COP/theoretical COP

Theoretical COP/actual COP

32. The superheating in a refrigeration cycle

Does not alter C.O.P.

None of these

Increases C.O.P.

Decreases C.O.P.

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

Saturated liquid

Superheated vapour

Wet vapour

Dry saturated vapour

34. 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)

(td₂ - td₃)/(td₃ - td₁)

(td₃ - td₁)/(td₂ - td₃)

(td₃ - td₂)/(td₃ - td₁)

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

Direct

Compression

Indirect

Absorption

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

Remain unaffected

Decrease

May increase or decrease depending on the type of refrigerant used

Increase

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

Condenser and expansion valve

Expansion valve and evaporator

Compressor and condenser

Compressor and evaporator

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

None of these

Relative

Absolute

Specific

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

NH3

Freon-22

Freon-12

CO2

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

Halide torch

Soap and water

All of these

Sulphur sticks

Page 5 of 5

41. Moisture in Freon refrigeration system causes

Freezing automatic regulating valve

Corrosion of whole system

Ineffective refrigeration

High power consumption

42. Refrigeration in aeroplanes usually employs the following refrigerant

CO2

Freon-22

Air

Freon-11

43. The sub-cooling in a refrigeration cycle

None of these

Does not alter C.O.P.

Increases C.O.P.

Decreases C.O.P.

44. The specific humidity during dehumidification process

Remains constant

Decreases

Increases

None of these

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

Ammonia

Carbon dioxide

R-12

Sulphur dioxide

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Refrigeration & Air-Conditioning Practice Set-4

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