Refrigeration & Air-Conditioning Practice Set-4

June 7, 2021

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

Dry saturated vapour

Wet vapour

Superheated vapour

Saturated liquid

2. 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 is lower than the dew point temperature of the incoming stream

Of adiabatic saturation of incoming stream

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

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

None of these

Lower than

Same as

Higher than

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

R-12

Ammonia

Sulphur dioxide

Carbon dioxide

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

Heat of compression

All of the above

Enthalpy increase in compressor

Work done by compressor

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

Halide torch

Sulphur sticks

All of these

Soap and water

7. Which of the following statement is correct?

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

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

8. Vapour compression refrigeration is somewhat like

Reversed Carnot cycle

Carnot cycle

None of the above

Rankine’s cycle

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

R-12

Carbon dioxide

Ammonia

Sulphur dioxide

10. 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)

(td₂ - td₃)/(td₃ - td₁)

(td₃ - td₁)/(td₂ - td₃)

(td₃ - td₂)/(td₃ - td₁)

(td₃ - td₁)/(td₃ - td₂)

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11. 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 expansion or throttle valve

After passing through the condenser

12. Moisture in Freon refrigeration system causes

Corrosion of whole system

High power consumption

Ineffective refrigeration

Freezing automatic regulating valve

13. 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

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

Will remain unaffected

Will be higher

14. Refrigeration in aeroplanes usually employs the following refrigerant

Freon-11

CO2

Air

Freon-22

15. 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

3 kW

1 kW

4 kW

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

Ice at 4°C

Water at 0°C

Solid and dry ice

Mixture of ice and water under equilibrium conditions

17. Air refrigeration operates on

Reversed Carnot cycle

Carnot cycle

Brayton cycle

Rankine’s cycle

18. The advantage of dry compression is that

It permits complete evaporation in the evaporator

It results in high volumetric and mechanical efficiency

It permits higher speeds to be used

All of the above

19. The Freon group of refrigerants are

Halocarbon refrigerants

Hydrocarbon refrigerants

Zoetrope refrigerants

Inorganic refrigerants

20. 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

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

Absorption

Indirect

Direct

Compression

22. The superheating in a refrigeration cycle

Decreases C.O.P.

Increases C.O.P.

Does not alter C.O.P.

None of these

23. 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 60% RH

26°C DBT and 50% RH

24. Ammonia absorption refrigeration cycle requires

Zero work input

Nearly same work input as for vapour compression cycle

Maximum work input

Very little work input

25. During cooling and dehumidification, dry bulb temperature

Decreases

Remains constant

None of these

Increases

26. Air conditioning means

All of these

Cooling

Heating

Dehumidifying

27. The specific humidity during dehumidification process

Decreases

None of these

Remains constant

Increases

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

Freon-22

CO2

NH3

Freon-12

29. Superheating in a refrigeration cycle

Other factors decide C.O.P

C.O.P remains unaltered

Increases C.O.P

Decreases C.O.P

30. The relative coefficient of performance is

Theoretical COP/actual COP

Actual COP/theoretical COP

Actual COP × theoretical COP

None of these

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

None of the above

Room sensible heat load only

Both room sensible heat and latent heat loads

Room latent heat load only

32. 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

33. 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

Remain unaffected

Decrease

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

Flooded

Dry

None of these

DX coil

35. The specific humidity during heating and humidification process.

Remains constant

None of these

Decreases

Increases

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)

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

μ/[1 - (1 - μ) (Ps/Pb)]

0.622 Pv / (Pb - Pv)

None of these

37. During sensible cooling,

Relative humidity remains constant

Specific humidity increases

Wet bulb temperature increases

Partial pressure of vapour remains constant

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

Effective temperature

None of these

Dew point temperature

Mean radiant temperature

39. 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

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

Less than 2 kg

There is no such consideration

More than 10 kg

More than or equal to 3.65 kg

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41. 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)

(hA - h2)/ (h1 - h2)

(h2 - hA)/ (h1 - h2)

42. The sub-cooling in a refrigeration cycle

None of these

Increases C.O.P.

Does not alter C.O.P.

Decreases C.O.P.

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

Equal

High

Small

Anything

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

Expansion valve and evaporator

Condenser and expansion valve

Compressor and condenser

Compressor and evaporator

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

None of these

Specific

Relative

Absolute

Refrigeration & Air-Conditioning Practice Set-4

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