Refrigeration & Air-Conditioning Practice Set-4

June 7, 2021

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1. 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

2. 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)

(td₂ - td₃)/(td₃ - td₁)

(td₃ - td₁)/(td₂ - td₃)

3. 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

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

Freon-12

NH3

CO2

Freon-22

5. 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

Effective temperature

Dew point temperature

None of these

6. Moisture in Freon refrigeration system causes

Corrosion of whole system

High power consumption

Ineffective refrigeration

Freezing automatic regulating valve

7. The superheating in a refrigeration cycle

Decreases C.O.P.

Does not alter C.O.P.

None of these

Increases C.O.P.

8. 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 - h2)/ (h1 - h2)

(hA - h1)/ (h2 - h1)

(h1 - h2)/ (hA - h2)

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

Flooded

None of these

DX coil

Dry

10. The advantage of dry compression is that

It permits complete evaporation in the evaporator

All of the above

It results in high volumetric and mechanical efficiency

It permits higher speeds to be used

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11. Air conditioning means

Cooling

Dehumidifying

Heating

All of these

12. Which of the following statement is correct?

All of these

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

The constant enthalpy lines are also constant wet bulb temperature lines

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

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

Metering of the refrigerant liquid

Compression of the refrigerant vapour

Evaporation of the refrigerant liquid

Condensation of the refrigerant vapour

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

None of these

Absolute

Specific

Relative

15. Air refrigeration operates on

Reversed Carnot cycle

Carnot cycle

Brayton cycle

Rankine’s cycle

16. Vapour compression refrigeration is somewhat like

None of the above

Rankine’s cycle

Reversed Carnot cycle

Carnot cycle

17. 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

1 kW

3 kW

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

Before passing through the condenser

After passing through the condenser

Before entering the compressor

After passing through the expansion or throttle valve

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

Higher than

Lower than

None of these

Same as

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

Ammonia

Carbon dioxide

R-12

Sulphur dioxide

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21. The specific humidity during dehumidification process

Increases

Remains constant

None of these

Decreases

22. 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

Will be lower

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

23. The relative coefficient of performance is

Theoretical COP/actual COP

Actual COP/theoretical COP

None of these

Actual COP × theoretical COP

24. Refrigeration in aeroplanes usually employs the following refrigerant

Freon-22

CO2

Freon-11

Air

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

26°C DBT and 60% RH

26°C DBT and 50% RH

20°C DBT and 60% RH

20°C DBT and 50% RH

26. 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

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

Soap and water

All of these

Halide torch

Sulphur sticks

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

Equal

High

Small

Anything

29. The specific humidity during heating and humidification process.

None of these

Decreases

Increases

Remains constant

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

Direct

Absorption

Compression

Indirect

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31. 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

32. During sensible cooling,

Relative humidity remains constant

Specific humidity increases

Wet bulb temperature increases

Partial pressure of vapour remains constant

33. During cooling and dehumidification, dry bulb temperature

Remains constant

None of these

Increases

Decreases

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

Carbon dioxide

Sulphur dioxide

R-12

Ammonia

35. 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

36. 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)

0.622 Pv / (Pb - Pv)

None of these

μ/[1 - (1 - μ) (Ps/Pb)]

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

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

Saturated liquid

Dry saturated vapour

Superheated vapour

Wet vapour

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

More than 10 kg

There is no such consideration

More than or equal to 3.65 kg

Less than 2 kg

39. Ammonia absorption refrigeration cycle requires

Very little work input

Maximum work input

Zero work input

Nearly same work input as for vapour compression cycle

40. The Freon group of refrigerants are

Zoetrope refrigerants

Hydrocarbon refrigerants

Halocarbon refrigerants

Inorganic refrigerants

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41. 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 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

42. The sub-cooling in a refrigeration cycle

None of these

Does not alter C.O.P.

Decreases C.O.P.

Increases C.O.P.

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

Room sensible heat load only

None of the above

Both room sensible heat and latent heat loads

Room latent heat load only

44. Superheating in a refrigeration cycle

Other factors decide C.O.P

C.O.P remains unaltered

Increases C.O.P

Decreases C.O.P

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

Compressor and evaporator

Condenser and expansion valve

Compressor and condenser

Expansion valve and evaporator

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Refrigeration & Air-Conditioning Practice Set-4

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