Refrigeration & Air-Conditioning Practice Set-4

June 7, 2021

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

Condenser and expansion valve

Expansion valve and evaporator

Compressor and condenser

Compressor and evaporator

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

Before entering the compressor

After passing through the condenser

After passing through the expansion or throttle valve

Before passing through the condenser

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

Soap and water

Sulphur sticks

All of these

Halide torch

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

R-12

Sulphur dioxide

Ammonia

Carbon dioxide

5. 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

6. Moisture in Freon refrigeration system causes

Corrosion of whole system

High power consumption

Ineffective refrigeration

Freezing automatic regulating valve

7. 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

8. Air conditioning means

Cooling

Dehumidifying

All of these

Heating

9. 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

4 kW

2 kW

1 kW

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

Dew point temperature

Mean radiant temperature

Effective temperature

None of these

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11. The specific humidity during dehumidification process

Increases

None of these

Decreases

Remains constant

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

Superheated vapour

Dry saturated vapour

Saturated liquid

Wet vapour

13. 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

14. The Freon group of refrigerants are

Inorganic refrigerants

Zoetrope refrigerants

Halocarbon refrigerants

Hydrocarbon refrigerants

15. The relative coefficient of performance is

Actual COP × theoretical COP

Theoretical COP/actual COP

Actual COP/theoretical COP

None of these

16. The superheating in a refrigeration cycle

Does not alter C.O.P.

Increases C.O.P.

Decreases C.O.P.

None of these

17. The specific humidity during heating and humidification process.

Remains constant

Decreases

None of these

Increases

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

Anything

High

Small

Equal

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

None of the above

Room sensible heat load only

Room latent heat load only

Both room sensible heat and latent heat loads

20. 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 dry bulb and wet bulb temperatures of the incoming stream

Of adiabatic saturation of incoming stream

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

Page 3 of 5

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

Ice at 4°C

Mixture of ice and water under equilibrium conditions

Water at 0°C

Solid and dry ice

22. 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 50% RH

26°C DBT and 60% RH

23. 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

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

Carbon dioxide

R-12

Sulphur dioxide

Ammonia

25. Air refrigeration operates on

Carnot cycle

Reversed Carnot cycle

Rankine’s cycle

Brayton cycle

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

Absorption

Indirect

Compression

Direct

27. 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)

(hA - h2)/ (h1 - h2)

(h2 - hA)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

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

Same as

Lower than

None of these

Higher than

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

Increase

May increase or decrease depending on the type of refrigerant used

Remain unaffected

Decrease

30. During sensible cooling,

Relative humidity remains constant

Wet bulb temperature increases

Partial pressure of vapour remains constant

Specific humidity increases

Page 4 of 5

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

Freon-12

CO2

NH3

Freon-22

32. Superheating in a refrigeration cycle

Increases C.O.P

Decreases C.O.P

Other factors decide C.O.P

C.O.P remains unaltered

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

Heat of compression

Enthalpy increase in compressor

All of the above

Work done by compressor

34. 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)

(td₃ - td₁)/(td₂ - td₃)

(td₂ - td₃)/(td₃ - td₁)

35. 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

Will remain unaffected

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

Will be lower

36. Vapour compression refrigeration is somewhat like

Reversed Carnot cycle

None of the above

Rankine’s cycle

Carnot cycle

37. Which of the following statement is correct?

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

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

The constant enthalpy lines are also constant wet bulb temperature lines

All of these

38. During cooling and dehumidification, dry bulb temperature

Decreases

Remains constant

Increases

None of these

39. The sub-cooling in a refrigeration cycle

Increases C.O.P.

Decreases C.O.P.

None of these

Does not alter C.O.P.

40. Refrigeration in aeroplanes usually employs the following refrigerant

Air

Freon-22

CO2

Freon-11

Page 5 of 5

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

Flooded

DX coil

None of these

Dry

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

Relative

Specific

None of these

Absolute

43. 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)

None of these

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

0.622 Pv / (Pb - Pv)

μ/[1 - (1 - μ) (Ps/Pb)]

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

Condensation of the refrigerant vapour

Metering of the refrigerant liquid

Compression of the refrigerant vapour

Evaporation of the refrigerant liquid

45. Ammonia absorption refrigeration cycle requires

Zero work input

Nearly same work input as for vapour compression cycle

Maximum work input

Very little work input

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Refrigeration & Air-Conditioning Practice Set-4

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