Refrigeration & Air-Conditioning Practice Set-4

Page 1 of 5

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

Compression of the refrigerant vapour

Metering of the refrigerant liquid

Evaporation of the refrigerant liquid

Condensation of the refrigerant vapour

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

Halide torch

Sulphur sticks

All of these

Soap and water

3. The superheating in a refrigeration cycle

Increases C.O.P.

Does not alter C.O.P.

Decreases C.O.P.

None of these

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

High

Anything

Small

Equal

5. 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

6

1.2

0.2

5

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

26°C DBT and 60% RH

20°C DBT and 50% RH

26°C DBT and 50% RH

20°C DBT and 60% RH

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

Wet vapour

Saturated liquid

Dry saturated vapour

Superheated vapour

8. 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)]

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

Both room sensible heat and latent heat loads

Room latent heat load only

None of the above

Room sensible heat load only

10. In order to cool and dehumidify a stream of moist air, it must be passed over the coil at a temperature

Of adiabatic saturation of 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

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

Page 2 of 5

11. The specific humidity during dehumidification process

None of these

Remains constant

Decreases

Increases

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

Water at 0°C

Solid and dry ice

Mixture of ice and water under equilibrium conditions

Ice at 4°C

13. The Freon group of refrigerants are

Zoetrope refrigerants

Halocarbon refrigerants

Inorganic refrigerants

Hydrocarbon refrigerants

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

After passing through the condenser

Before entering the compressor

After passing through the expansion or throttle valve

Before passing through the condenser

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

4 kW

1 kW

3 kW

2 kW

16. The specific humidity during heating and humidification process.

Increases

None of these

Decreases

Remains constant

17. Air conditioning means

Cooling

Dehumidifying

All of these

Heating

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

Less

Same

More

More or less depending on ambient conditions

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

Effective temperature

Dew point temperature

None of these

Mean radiant temperature

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

Flooded

DX coil

Dry

None of these

Page 3 of 5

21. 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

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

Absolute

Relative

None of these

Specific

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

There is no such consideration

Less than 2 kg

More than 10 kg

More than or equal to 3.65 kg

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

Same as

Lower than

Higher than

None of these

25. The advantage of dry compression is that

It results in high volumetric and mechanical efficiency

It permits complete evaporation in the evaporator

It permits higher speeds to be used

All of the above

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

Indirect

Compression

Direct

Absorption

27. The sub-cooling in a refrigeration cycle

Does not alter C.O.P.

Decreases C.O.P.

Increases C.O.P.

None of these

28. The relative coefficient of performance is

Actual COP × theoretical COP

Actual COP/theoretical COP

None of these

Theoretical COP/actual COP

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

Expansion valve and evaporator

Condenser and expansion valve

Compressor and condenser

Compressor and evaporator

30. Ammonia absorption refrigeration cycle requires

Maximum work input

Nearly same work input as for vapour compression cycle

Very little work input

Zero work input

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

Sulphur dioxide

Carbon dioxide

Ammonia

R-12

32. Air refrigeration operates on

Reversed Carnot cycle

Rankine’s cycle

Carnot cycle

Brayton cycle

33. Which of the following statement is correct?

All of these

The constant enthalpy lines are also constant wet bulb temperature lines

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

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

34. Refrigeration in aeroplanes usually employs the following refrigerant

Freon-22

CO2

Air

Freon-11

35. Moisture in Freon refrigeration system causes

Freezing automatic regulating valve

Corrosion of whole system

Ineffective refrigeration

High power consumption

36. 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 - h1)/ (h2 - h1)

(h2 - hA)/ (h1 - h2)

(hA - h2)/ (h1 - h2)

37. During cooling and dehumidification, dry bulb temperature

None of these

Decreases

Increases

Remains constant

38. Vapour compression refrigeration is somewhat like

Carnot cycle

None of the above

Rankine’s cycle

Reversed Carnot cycle

39. 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

Will be higher

Will remain unaffected

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

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

Increase

Remain unaffected

May increase or decrease depending on the type of refrigerant used

Decrease

Page 5 of 5

41. During sensible cooling,

Specific humidity increases

Wet bulb temperature increases

Relative humidity remains constant

Partial pressure of vapour remains constant

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

R-12

Carbon dioxide

Ammonia

Sulphur dioxide

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

CO2

Freon-22

NH3

Freon-12

44. Superheating in a refrigeration cycle

Increases C.O.P

C.O.P remains unaltered

Decreases C.O.P

Other factors decide C.O.P

45. 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 - td₂)/(td₃ - td₁)

(td₃ - td₁)/(td₃ - td₂)

(td₂ - td₃)/(td₃ - td₁)

Refrigeration & Air-Conditioning Practice Set-4

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