Refrigeration & Air-Conditioning Practice Set-4

June 7, 2021

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

Both room sensible heat and latent heat loads

Room sensible heat load only

Room latent heat load only

None of the above

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

Equal

High

Small

Anything

3. Air refrigeration operates on

Reversed Carnot cycle

Brayton cycle

Carnot cycle

Rankine’s cycle

4. 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

5. During sensible cooling,

Partial pressure of vapour remains constant

Relative humidity remains constant

Wet bulb temperature increases

Specific humidity increases

6. The advantage of dry compression is that

It results in high volumetric and mechanical efficiency

It permits complete evaporation in the evaporator

All of the above

It permits higher speeds to be used

7. Moisture in Freon refrigeration system causes

Ineffective refrigeration

High power consumption

Corrosion of whole system

Freezing automatic regulating valve

8. Superheating in a refrigeration cycle

C.O.P remains unaltered

Other factors decide C.O.P

Decreases C.O.P

Increases C.O.P

9. Vapour compression refrigeration is somewhat like

Carnot cycle

Reversed Carnot cycle

None of the above

Rankine’s cycle

10. 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 be higher

Will remain unaffected

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11. 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)

μ/[1 - (1 - μ) (Ps/Pb)]

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

None of these

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

Flooded

DX coil

None of these

Dry

13. 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

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

None of these

Relative

Specific

Absolute

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

Sulphur sticks

All of these

Soap and water

Halide torch

16. 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)

(h1 - h2)/ (hA - h2)

(hA - h2)/ (h1 - h2)

(hA - h1)/ (h2 - h1)

17. 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

18. The specific humidity during dehumidification process

Increases

None of these

Remains constant

Decreases

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

R-12

Sulphur dioxide

Carbon dioxide

Ammonia

20. The sub-cooling in a refrigeration cycle

None of these

Decreases C.O.P.

Does not alter C.O.P.

Increases C.O.P.

Page 3 of 5

21. 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

22. Refrigeration in aeroplanes usually employs the following refrigerant

Freon-11

CO2

Air

Freon-22

23. The Freon group of refrigerants are

Hydrocarbon refrigerants

Inorganic refrigerants

Zoetrope refrigerants

Halocarbon refrigerants

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

More or less depending on ambient conditions

Less

Same

25. The specific humidity during heating and humidification process.

Decreases

Remains constant

None of these

Increases

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

Decrease

May increase or decrease depending on the type of refrigerant used

Increase

Remain unaffected

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

Freon-22

CO2

Freon-12

NH3

28. The superheating in a refrigeration cycle

None of these

Decreases C.O.P.

Increases C.O.P.

Does not alter C.O.P.

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

Ammonia

Sulphur dioxide

Carbon dioxide

R-12

30. Ammonia absorption refrigeration cycle requires

Maximum work input

Very little work input

Nearly same work input as for vapour compression cycle

Zero work input

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

Expansion valve and evaporator

Condenser and expansion valve

Compressor and evaporator

Compressor and condenser

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 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)/(td₂ - td₃)

(td₃ - td₁)/(td₃ - td₂)

(td₃ - td₂)/(td₃ - td₁)

(td₂ - td₃)/(td₃ - td₁)

34. Air conditioning means

Cooling

Heating

All of these

Dehumidifying

35. Which of the following statement is correct?

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

All of these

The constant enthalpy lines are also constant wet bulb temperature lines

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

36. 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

Effective temperature

Dew point temperature

Mean radiant temperature

37. During cooling and dehumidification, dry bulb temperature

Decreases

Remains constant

None of these

Increases

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

Compression of the refrigerant vapour

Metering of the refrigerant liquid

Condensation of the refrigerant vapour

Evaporation of the refrigerant liquid

39. 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

1 kW

2 kW

3 kW

4 kW

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

Compression

Absorption

Direct

Indirect

Page 5 of 5

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

All of the above

Work done by compressor

Enthalpy increase in compressor

Heat of compression

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

Wet vapour

Saturated liquid

Superheated vapour

Dry saturated vapour

43. The relative coefficient of performance is

Actual COP/theoretical COP

None of these

Theoretical COP/actual COP

Actual COP × theoretical COP

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

There is no such consideration

More than 10 kg

More than or equal to 3.65 kg

Less than 2 kg

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

Same as

None of these

Higher than

Lower than

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Refrigeration & Air-Conditioning Practice Set-4

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