Refrigeration & Air-Conditioning Practice Set-4

June 7, 2021

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Page 1 of 5

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

20°C DBT and 50% RH

26°C DBT and 60% RH

20°C DBT and 60% RH

26°C DBT and 50% RH

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

Relative

None of these

Specific

Absolute

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

Carbon dioxide

R-12

Sulphur dioxide

Ammonia

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

Remain unaffected

Increase

Decrease

May increase or decrease depending on the type of refrigerant used

5. During cooling and dehumidification, dry bulb temperature

Remains constant

Increases

None of these

Decreases

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

Work done by compressor

Heat of compression

Enthalpy increase in compressor

All of the above

7. Moisture in Freon refrigeration system causes

Corrosion of whole system

Ineffective refrigeration

Freezing automatic regulating valve

High power consumption

8. Air conditioning means

Heating

All of these

Dehumidifying

Cooling

9. 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)]

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

0.622 Pv / (Pb - Pv)

None of these

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

Small

Equal

Anything

High

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11. The advantage of dry compression is that

It permits complete evaporation in the evaporator

It results in high volumetric and mechanical efficiency

All of the above

It permits higher speeds to be used

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

R-12

Ammonia

Carbon dioxide

Sulphur dioxide

13. The superheating in a refrigeration cycle

Increases C.O.P.

Decreases C.O.P.

Does not alter C.O.P.

None of these

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

Before entering the compressor

After passing through the expansion or throttle valve

Before passing through the condenser

After passing through the condenser

15. 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

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

Evaporation of the refrigerant liquid

Condensation of the refrigerant vapour

Compression of the refrigerant vapour

Metering of the refrigerant liquid

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

Effective temperature

Mean radiant temperature

Dew point temperature

None of these

18. The sub-cooling in a refrigeration cycle

Increases C.O.P.

Does not alter C.O.P.

Decreases C.O.P.

None of these

19. Ammonia absorption refrigeration cycle requires

Maximum work input

Zero work input

Nearly same work input as for vapour compression cycle

Very little work input

20. During sensible cooling,

Relative humidity remains constant

Specific humidity increases

Partial pressure of vapour remains constant

Wet bulb temperature increases

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21. Vapour compression refrigeration is somewhat like

Rankine’s cycle

Carnot cycle

None of the above

Reversed Carnot cycle

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

Saturated liquid

Dry saturated vapour

Wet vapour

Superheated vapour

23. The relative coefficient of performance is

None of these

Actual COP/theoretical COP

Actual COP × theoretical COP

Theoretical COP/actual COP

24. Air refrigeration operates on

Carnot cycle

Brayton cycle

Rankine’s cycle

Reversed Carnot cycle

25. Superheating in a refrigeration cycle

C.O.P remains unaltered

Other factors decide C.O.P

Decreases C.O.P

Increases C.O.P

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

Freon-22

Freon-12

NH3

CO2

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

Sulphur sticks

Soap and water

Halide torch

All of these

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

Lower than

None of these

Same as

Higher than

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 wet bulb and dew point temperatures of the incoming stream

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

Which is lower than the dew point temperature of the incoming stream

Of adiabatic saturation of incoming stream

30. 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

1 kW

2 kW

4 kW

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

Compressor and evaporator

Condenser and expansion valve

Expansion valve and evaporator

Compressor and condenser

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

DX coil

None of these

Flooded

Dry

33. The Freon group of refrigerants are

Hydrocarbon refrigerants

Halocarbon refrigerants

Inorganic refrigerants

Zoetrope refrigerants

34. The specific humidity during heating and humidification process.

None of these

Decreases

Increases

Remains constant

35. The specific humidity during dehumidification process

Increases

None of these

Remains constant

Decreases

36. 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 - td₁)/(td₃ - td₂)

(td₃ - td₂)/(td₃ - td₁)

37. Which of the following statement is correct?

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

The constant enthalpy lines are also constant wet bulb temperature lines

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

Room sensible heat load only

None of the above

Room latent heat load only

Both room sensible heat and latent heat loads

39. 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

40. 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

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

Will be lower

Will remain unaffected

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

Compression

Direct

Absorption

Indirect

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

Mixture of ice and water under equilibrium conditions

Ice at 4°C

Water at 0°C

Solid and dry ice

43. Refrigeration in aeroplanes usually employs the following refrigerant

CO2

Freon-22

Air

Freon-11

44. 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)

(h1 - h2)/ (hA - h2)

(hA - h2)/ (h1 - h2)

(h2 - hA)/ (h1 - h2)

(hA - h1)/ (h2 - h1)

45. 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

Refrigeration & Air-Conditioning Practice Set-4

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