Refrigeration & Air-Conditioning Practice Set-4

June 7, 2021

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Page 1 of 5

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

R-12

Ammonia

Carbon dioxide

Sulphur dioxide

2. Air conditioning means

Heating

All of these

Dehumidifying

Cooling

3. 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

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

NH3

CO2

Freon-12

Freon-22

5. Which of the following statement is correct?

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

The constant enthalpy lines are also constant wet bulb temperature lines

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

All of these

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

Mixture of ice and water under equilibrium conditions

Water at 0°C

Ice at 4°C

Solid and dry ice

7. The relative coefficient of performance is

Actual COP × theoretical COP

Theoretical COP/actual COP

Actual COP/theoretical COP

None of these

8. During cooling and dehumidification, dry bulb temperature

Increases

Decreases

None of these

Remains constant

9. 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 - td₂)/(td₃ - td₁)

(td₂ - td₃)/(td₃ - td₁)

(td₃ - td₁)/(td₃ - td₂)

(td₃ - td₁)/(td₂ - td₃)

10. Superheating in a refrigeration cycle

C.O.P remains unaltered

Other factors decide C.O.P

Decreases C.O.P

Increases C.O.P

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

Halide torch

Sulphur sticks

All of these

Soap and water

12. Ammonia absorption refrigeration cycle requires

Nearly same work input as for vapour compression cycle

Zero work input

Very little work input

Maximum work input

13. The advantage of dry compression is that

All of the above

It permits higher speeds to be used

It permits complete evaporation in the evaporator

It results in high volumetric and mechanical efficiency

14. In refrigerator, liquid receiver is required between condenser and flow controlling device, if quantity of refrigerant for system is

More than 10 kg

Less than 2 kg

There is no such consideration

More than or equal to 3.65 kg

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

Condenser and expansion valve

Expansion valve and evaporator

Compressor and evaporator

Compressor and condenser

16. Refrigeration in aeroplanes usually employs the following refrigerant

CO2

Air

Freon-11

Freon-22

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

Small

High

Equal

Anything

18. Air refrigeration operates on

Reversed Carnot cycle

Rankine’s cycle

Carnot cycle

Brayton cycle

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

Lower than

Higher than

Same as

None of these

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

None of the above

Room latent heat load only

Both room sensible heat and latent heat loads

Room sensible heat load only

Page 3 of 5

21. 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 wet bulb and dew point temperatures 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 is lower than the dew point temperature of the incoming stream

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

After passing through the condenser

After passing through the expansion or throttle valve

Before passing through the condenser

Before entering the compressor

23. The specific humidity during dehumidification process

Remains constant

None of these

Decreases

Increases

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

Condensation of the refrigerant vapour

Metering of the refrigerant liquid

Evaporation of the refrigerant liquid

Compression of the refrigerant vapour

25. Vapour compression refrigeration is somewhat like

Carnot cycle

Reversed Carnot cycle

None of the above

Rankine’s cycle

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

Relative

Absolute

None of these

Specific

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

Absorption

Compression

Direct

Indirect

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

Effective temperature

Dew point temperature

Mean radiant temperature

None of these

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

Dry

Flooded

None of these

DX coil

30. The superheating in a refrigeration cycle

Increases C.O.P.

Decreases C.O.P.

None of these

Does not alter C.O.P.

Page 4 of 5

31. Moisture in Freon refrigeration system causes

Freezing automatic regulating valve

Corrosion of whole system

High power consumption

Ineffective refrigeration

32. 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

1 kW

3 kW

33. The sub-cooling in a refrigeration cycle

None of these

Increases C.O.P.

Decreases C.O.P.

Does not alter C.O.P.

34. 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

Decrease

Remain unaffected

Increase

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

Carbon dioxide

Sulphur dioxide

Ammonia

R-12

36. The specific humidity during heating and humidification process.

None of these

Increases

Remains constant

Decreases

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

26°C DBT and 60% RH

20°C DBT and 50% RH

20°C DBT and 60% RH

26°C DBT and 50% RH

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

Work done by compressor

Heat of compression

All of the above

Enthalpy increase in compressor

39. 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)

(hA - h1)/ (h2 - h1)

(h1 - h2)/ (hA - h2)

(h2 - hA)/ (h1 - h2)

(hA - h2)/ (h1 - h2)

40. The Freon group of refrigerants are

Inorganic refrigerants

Zoetrope refrigerants

Hydrocarbon refrigerants

Halocarbon refrigerants

Page 5 of 5

41. 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)]

0.622 Pv / (Pb - Pv)

None of these

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

42. During sensible cooling,

Relative humidity remains constant

Specific humidity increases

Partial pressure of vapour remains constant

Wet bulb temperature increases

43. 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

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

Will be lower

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

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

Dry saturated vapour

Saturated liquid

Superheated vapour

Wet vapour

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Refrigeration & Air-Conditioning Practice Set-4

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