Refrigeration & Air-Conditioning Practice Set-4

Page 1 of 5

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

None of these

Same as

Lower than

Higher than

2. 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

5

6

1.2

0.2

3. During cooling and dehumidification, dry bulb temperature

Increases

Decreases

Remains constant

None of these

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

More than or equal to 3.65 kg

More than 10 kg

Less than 2 kg

There is no such consideration

5. 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

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

After passing through the expansion or throttle valve

Before passing through the condenser

After passing through the condenser

Before entering the compressor

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

Saturated liquid

Superheated vapour

Dry saturated vapour

Wet vapour

8. The condensing pressure due to the presence of non-condensable gases, as compared to that actually required for condensing temperatures without non-condensable gases,

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

Will be higher

Will remain unaffected

Will be lower

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

All of the above

Enthalpy increase in compressor

Work done by compressor

Heat of compression

10. The advantage of dry compression is that

All of the above

It permits complete evaporation in the evaporator

It permits higher speeds to be used

It results in high volumetric and mechanical efficiency

Page 2 of 5

11. Air refrigeration operates on

Reversed Carnot cycle

Carnot cycle

Rankine’s cycle

Brayton cycle

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

Small

High

Anything

Equal

13. The superheating in a refrigeration cycle

Increases C.O.P.

Does not alter C.O.P.

None of these

Decreases C.O.P.

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

More

More or less depending on ambient conditions

Same

Less

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

Both room sensible heat and latent heat loads

None of the above

Room latent heat load only

Room sensible heat load only

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

Flooded

Dry

DX coil

None of these

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

Halide torch

Soap and water

All of these

Sulphur sticks

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

Freon-12

CO2

Freon-22

NH3

19. The specific humidity during dehumidification process

Decreases

None of these

Increases

Remains constant

20. 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

Decrease

Remain unaffected

Page 3 of 5

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

Compression

Indirect

Absorption

Direct

22. Which of the following statement is correct?

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

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

23. The specific humidity during heating and humidification process.

None of these

Increases

Remains constant

Decreases

24. The relative coefficient of performance is

Theoretical COP/actual COP

Actual COP × theoretical COP

None of these

Actual COP/theoretical COP

25. Moisture in Freon refrigeration system causes

Corrosion of whole system

High power consumption

Freezing automatic regulating valve

Ineffective refrigeration

26. 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

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

Of adiabatic saturation of incoming stream

Which is lower than the dew point temperature of the incoming stream

27. Air conditioning means

Cooling

Dehumidifying

All of these

Heating

28. Vapour compression refrigeration is somewhat like

Rankine’s cycle

Reversed Carnot cycle

None of the above

Carnot cycle

29. The Freon group of refrigerants are

Halocarbon refrigerants

Zoetrope refrigerants

Hydrocarbon refrigerants

Inorganic refrigerants

30. 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)

(td₂ - td₃)/(td₃ - td₁)

(td₃ - td₁)/(td₂ - td₃)

(td₃ - td₁)/(td₃ - td₂)

(td₃ - td₂)/(td₃ - td₁)

Page 4 of 5

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

Ammonia

Carbon dioxide

Sulphur dioxide

R-12

32. 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

33. 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)

34. The sub-cooling in a refrigeration cycle

Decreases C.O.P.

Increases C.O.P.

Does not alter C.O.P.

None of these

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

Expansion valve and evaporator

Compressor and condenser

Condenser and expansion valve

Compressor and evaporator

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

None of these

Absolute

Relative

Specific

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

Ammonia

R-12

Carbon dioxide

Sulphur dioxide

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

Solid and dry ice

Mixture of ice and water under equilibrium conditions

Water at 0°C

Ice at 4°C

39. Refrigeration in aeroplanes usually employs the following refrigerant

Freon-11

Air

Freon-22

CO2

40. 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

0.622 Pv / (Pb - Pv)

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

μ/[1 - (1 - μ) (Ps/Pb)]

Page 5 of 5

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

Compression of the refrigerant vapour

Condensation of the refrigerant vapour

Metering of the refrigerant liquid

Evaporation of the refrigerant liquid

42. 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

Mean radiant temperature

None of these

43. Superheating in a refrigeration cycle

Increases C.O.P

C.O.P remains unaltered

Decreases C.O.P

Other factors decide C.O.P

44. During sensible cooling,

Wet bulb temperature increases

Specific humidity increases

Relative humidity remains constant

Partial pressure of vapour remains constant

45. Ammonia absorption refrigeration cycle requires

Very little work input

Nearly same work input as for vapour compression cycle

Zero work input

Maximum work input

Refrigeration & Air-Conditioning Practice Set-4

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