Refrigeration & Air-Conditioning Practice Set-4

June 7, 2021

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Page 1 of 5

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

Equal

Small

Anything

High

2. 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 lower

Will remain unaffected

Will be higher

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

3. Vapour compression refrigeration is somewhat like

Rankine’s cycle

Carnot cycle

None of the above

Reversed Carnot cycle

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

Specific

Relative

None of these

Absolute

5. The sub-cooling in a refrigeration cycle

None of these

Does not alter C.O.P.

Increases C.O.P.

Decreases C.O.P.

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

Carbon dioxide

Ammonia

R-12

Sulphur dioxide

7. 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 - td₁)/(td₃ - td₂)

(td₃ - td₂)/(td₃ - td₁)

(td₂ - td₃)/(td₃ - td₁)

8. The superheating in a refrigeration cycle

Increases C.O.P.

Decreases C.O.P.

Does not alter C.O.P.

None of these

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

R-12

Ammonia

Sulphur dioxide

Carbon dioxide

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

Superheated vapour

Wet vapour

Dry saturated vapour

Saturated liquid

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

Flooded

Dry

DX coil

None of these

12. Which of the following statement is correct?

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

The constant enthalpy lines are also constant wet bulb temperature lines

13. 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

14. The advantage of dry compression is that

It permits higher speeds to be used

It results in high volumetric and mechanical efficiency

It permits complete evaporation in the evaporator

All of the above

15. Refrigeration in aeroplanes usually employs the following refrigerant

Freon-11

CO2

Air

Freon-22

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

Direct

Indirect

Absorption

Compression

17. 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

None of these

Effective temperature

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

Remain unaffected

Increase

May increase or decrease depending on the type of refrigerant used

Decrease

19. The relative coefficient of performance is

None of these

Actual COP/theoretical COP

Theoretical COP/actual COP

Actual COP × theoretical COP

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

Less

Same

More or less depending on ambient conditions

Page 3 of 5

21. Superheating in a refrigeration cycle

C.O.P remains unaltered

Decreases C.O.P

Other factors decide C.O.P

Increases C.O.P

22. During cooling and dehumidification, dry bulb temperature

Increases

Remains constant

Decreases

None of these

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

Solid and dry ice

Ice at 4°C

Mixture of ice and water under equilibrium conditions

Water at 0°C

24. 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

0.622 Pv / (Pb - Pv)

μ/[1 - (1 - μ) (Ps/Pb)]

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

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 - h1)/ (h2 - h1)

(hA - h2)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

26. The specific humidity during dehumidification process

Increases

Decreases

Remains constant

None of these

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

Room latent heat load only

None of the above

Room sensible heat load only

Both room sensible heat and latent heat loads

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

Compressor and condenser

Compressor and evaporator

Expansion valve and evaporator

Condenser and expansion valve

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

Freon-22

Freon-12

CO2

NH3

30. 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

1.2

0.2

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31. Ammonia absorption refrigeration cycle requires

Maximum work input

Very little work input

Nearly same work input as for vapour compression cycle

Zero work input

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

Condensation of the refrigerant vapour

Compression of the refrigerant vapour

Metering of the refrigerant liquid

Evaporation of the refrigerant liquid

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

All of these

Sulphur sticks

Soap and water

Halide torch

34. During sensible cooling,

Relative humidity remains constant

Specific humidity increases

Partial pressure of vapour remains constant

Wet bulb temperature increases

35. 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

Of adiabatic saturation of incoming stream

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

36. Moisture in Freon refrigeration system causes

Ineffective refrigeration

Corrosion of whole system

Freezing automatic regulating valve

High power consumption

37. The Freon group of refrigerants are

Zoetrope refrigerants

Halocarbon refrigerants

Inorganic refrigerants

Hydrocarbon refrigerants

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

None of these

Same as

Lower than

Higher than

39. Air conditioning means

All of these

Cooling

Dehumidifying

Heating

40. Air refrigeration operates on

Brayton cycle

Rankine’s cycle

Reversed Carnot cycle

Carnot cycle

Page 5 of 5

41. 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

3 kW

2 kW

1 kW

4 kW

42. 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 10 kg

There is no such consideration

More than or equal to 3.65 kg

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

Heat of compression

Work done by compressor

Enthalpy increase in compressor

All of the above

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

20°C DBT and 50% RH

20°C DBT and 60% RH

26°C DBT and 50% RH

26°C DBT and 60% RH

45. The specific humidity during heating and humidification process.

None of these

Remains constant

Increases

Decreases

Refrigeration & Air-Conditioning Practice Set-4

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