Refrigeration & Air-Conditioning Practice Set-4

June 7, 2021

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Page 1 of 5

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

Ammonia

R-12

Sulphur dioxide

Carbon dioxide

2. 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

4 kW

1 kW

3. 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 - h2)/ (h1 - h2)

(h2 - hA)/ (h1 - h2)

(hA - h1)/ (h2 - h1)

(h1 - h2)/ (hA - h2)

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

Room latent heat load only

Room sensible heat load only

None of the above

Both room sensible heat and latent heat loads

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

Indirect

Direct

Compression

Absorption

6. Moisture in Freon refrigeration system causes

Freezing automatic regulating valve

Corrosion of whole system

High power consumption

Ineffective refrigeration

7. The sub-cooling in a refrigeration cycle

None of these

Increases C.O.P.

Decreases C.O.P.

Does not alter C.O.P.

8. The specific humidity during dehumidification process

None of these

Increases

Remains constant

Decreases

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

More or less depending on ambient conditions

Same

Less

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

Evaporation of the refrigerant liquid

Compression of the refrigerant vapour

Metering of the refrigerant liquid

Condensation of the refrigerant vapour

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

Relative

Absolute

None of these

Specific

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

Equal

High

Small

Anything

13. The superheating in a refrigeration cycle

Decreases C.O.P.

None of these

Increases C.O.P.

Does not alter C.O.P.

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

Sulphur sticks

Halide torch

All of these

Soap and water

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

Superheated vapour

Wet vapour

Dry saturated vapour

Saturated liquid

16. During sensible cooling,

Partial pressure of vapour remains constant

Wet bulb temperature increases

Relative humidity remains constant

Specific humidity increases

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

None of these

DX coil

Flooded

Dry

18. The specific humidity during heating and humidification process.

None of these

Decreases

Increases

Remains constant

19. 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)

(td₃ - td₁)/(td₂ - td₃)

(td₂ - td₃)/(td₃ - td₁)

(td₃ - td₁)/(td₃ - td₂)

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

20°C DBT and 50% RH

26°C DBT and 60% RH

26°C DBT and 50% RH

20°C DBT and 60% RH

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

None of these

Dew point temperature

Effective temperature

Mean radiant temperature

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

After passing through the expansion or throttle valve

After passing through the condenser

Before entering the compressor

Before passing through the condenser

23. Ammonia absorption refrigeration cycle requires

Nearly same work input as for vapour compression cycle

Zero work input

Very little work input

Maximum work input

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

None of these

Same as

Lower than

Higher than

25. 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 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

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

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

Water at 0°C

Solid and dry ice

Ice at 4°C

Mixture of ice and water under equilibrium conditions

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

More than 10 kg

More than or equal to 3.65 kg

Less than 2 kg

There is no such consideration

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

NH3

CO2

Freon-12

Freon-22

29. Air refrigeration operates on

Carnot cycle

Brayton cycle

Rankine’s cycle

Reversed Carnot cycle

30. During cooling and dehumidification, dry bulb temperature

None of these

Remains constant

Decreases

Increases

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31. 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

All of these

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

32. Air conditioning means

Cooling

Heating

Dehumidifying

All of these

33. The Freon group of refrigerants are

Hydrocarbon refrigerants

Halocarbon refrigerants

Zoetrope refrigerants

Inorganic refrigerants

34. 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

35. Refrigeration in aeroplanes usually employs the following refrigerant

Air

Freon-22

CO2

Freon-11

36. Vapour compression refrigeration is somewhat like

Reversed Carnot cycle

None of the above

Rankine’s cycle

Carnot cycle

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

Sulphur dioxide

Carbon dioxide

R-12

Ammonia

38. 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

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

μ/[1 - (1 - μ) (Ps/Pb)]

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 advantage of dry compression is that

It results in high volumetric and mechanical efficiency

All of the above

It permits higher speeds to be used

It permits complete evaporation in the evaporator

Page 5 of 5

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

Decrease

Increase

May increase or decrease depending on the type of refrigerant used

Remain unaffected

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

Expansion valve and evaporator

Condenser and expansion valve

Compressor and condenser

Compressor and evaporator

43. Superheating in a refrigeration cycle

Decreases C.O.P

Other factors decide C.O.P

Increases C.O.P

C.O.P remains unaltered

44. 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

45. The relative coefficient of performance is

None of these

Theoretical COP/actual COP

Actual COP/theoretical COP

Actual COP × theoretical COP

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Refrigeration & Air-Conditioning Practice Set-4

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