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

Evaporation of the refrigerant liquid

Compression of the refrigerant vapour

Metering of the refrigerant liquid

Condensation of the refrigerant vapour

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

R-12

Ammonia

Sulphur dioxide

Carbon dioxide

3. Moisture in Freon refrigeration system causes

Freezing automatic regulating valve

Ineffective refrigeration

High power consumption

Corrosion of whole system

4. 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

5. 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

2 kW

3 kW

1 kW

6. The sub-cooling in a refrigeration cycle

Decreases C.O.P.

Does not alter C.O.P.

Increases C.O.P.

None of these

7. The relative coefficient of performance is

Theoretical COP/actual COP

Actual COP/theoretical COP

Actual COP × theoretical COP

None of these

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

None of the above

Both room sensible heat and latent heat loads

Room sensible heat load only

Room latent heat load only

9. The specific humidity during dehumidification process

Remains constant

None of these

Increases

Decreases

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

Halide torch

Sulphur sticks

Soap and water

All of these

Page 2 of 5

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

None of these

Dry

Flooded

DX coil

12. 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)

(hA - h2)/ (h1 - h2)

(hA - h1)/ (h2 - h1)

(h1 - h2)/ (hA - h2)

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

Indirect

Compression

Direct

Absorption

14. 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

μ/[1 - (1 - μ) (Ps/Pb)]

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

0.622 Pv / (Pb - Pv)

15. 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 remain unaffected

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

Will be higher

16. Vapour compression refrigeration is somewhat like

None of the above

Rankine’s cycle

Carnot cycle

Reversed Carnot cycle

17. 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

18. Air conditioning means

Dehumidifying

Heating

Cooling

All of these

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

20°C DBT and 50% RH

26°C DBT and 50% RH

26°C DBT and 60% RH

20°C DBT and 60% RH

20. The specific humidity during heating and humidification process.

Remains constant

None of these

Decreases

Increases

Page 3 of 5

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

Decrease

Increase

Remain unaffected

May increase or decrease depending on the type of refrigerant used

22. The Freon group of refrigerants are

Zoetrope refrigerants

Inorganic refrigerants

Halocarbon refrigerants

Hydrocarbon refrigerants

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

Absolute

None of these

Specific

Relative

24. Refrigeration in aeroplanes usually employs the following refrigerant

Freon-22

Freon-11

CO2

Air

25. During cooling and dehumidification, dry bulb temperature

Increases

Decreases

None of these

Remains constant

26. 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

27. 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

Less than 2 kg

More than or equal to 3.65 kg

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

More

Same

Less

More or less depending on ambient conditions

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

Same as

Lower than

Higher than

None of these

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

After passing through the condenser

Before entering the compressor

Before passing through the condenser

After passing through the expansion or throttle valve

Page 4 of 5

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

Condenser and expansion valve

Expansion valve and evaporator

Compressor and condenser

Compressor and evaporator

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

5

6

0.2

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

Dry saturated vapour

Wet vapour

Saturated liquid

Superheated vapour

34. During sensible cooling,

Wet bulb temperature increases

Specific humidity increases

Partial pressure of vapour remains constant

Relative humidity remains constant

35. Ammonia absorption refrigeration cycle requires

Maximum work input

Zero work input

Nearly same work input as for vapour compression cycle

Very little work input

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

Sulphur dioxide

R-12

Carbon dioxide

Ammonia

37. 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)

(td₂ - td₃)/(td₃ - td₁)

(td₃ - td₁)/(td₂ - td₃)

(td₃ - td₂)/(td₃ - td₁)

38. Which of the following statement is correct?

The constant enthalpy lines are also constant wet bulb temperature lines

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

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

All of these

39. The advantage of dry compression is that

It permits higher speeds to be used

It results in high volumetric and mechanical efficiency

All of the above

It permits complete evaporation in the evaporator

40. The superheating in a refrigeration cycle

Does not alter C.O.P.

Decreases C.O.P.

Increases C.O.P.

None of these

Page 5 of 5

41. Air refrigeration operates on

Reversed Carnot cycle

Rankine’s cycle

Brayton cycle

Carnot cycle

42. Superheating in a refrigeration cycle

Other factors decide C.O.P

Decreases C.O.P

C.O.P remains unaltered

Increases C.O.P

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

Freon-12

CO2

Freon-22

NH3

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

All of the above

Heat of compression

Enthalpy increase in compressor

Work done by compressor

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

High

Equal

Small

Anything

Refrigeration & Air-Conditioning Practice Set-4

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