Refrigeration & Air-Conditioning Practice Set-4

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1. Air conditioning means

Heating

Cooling

All of these

Dehumidifying

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

0.2

1.2

6

3. 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

3 kW

1 kW

2 kW

4. The superheating in a refrigeration cycle

Increases C.O.P.

None of these

Does not alter C.O.P.

Decreases C.O.P.

5. 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

Of adiabatic saturation of incoming stream

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

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

May increase or decrease depending on the type of refrigerant used

Decrease

Remain unaffected

Increase

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

Wet vapour

Superheated vapour

Saturated liquid

Dry saturated vapour

8. The Freon group of refrigerants are

Halocarbon refrigerants

Inorganic refrigerants

Zoetrope refrigerants

Hydrocarbon refrigerants

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

Sulphur dioxide

Ammonia

R-12

Carbon dioxide

10. 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

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11. 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 - td₂)/(td₃ - td₁)

(td₃ - td₁)/(td₃ - td₂)

(td₃ - td₁)/(td₂ - td₃)

(td₂ - td₃)/(td₃ - td₁)

12. 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

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

Soap and water

Sulphur sticks

Halide torch

All of these

14. Ammonia absorption refrigeration cycle requires

Zero work input

Maximum work input

Nearly same work input as for vapour compression cycle

Very little work input

15. 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

16. The specific humidity during heating and humidification process.

Increases

None of these

Remains constant

Decreases

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

Absolute

Relative

Specific

None of these

18. 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)

(h2 - hA)/ (h1 - h2)

(hA - h2)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

19. Which of the following statement is correct?

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

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

20. During sensible cooling,

Relative humidity remains constant

Partial pressure of vapour remains constant

Wet bulb temperature increases

Specific humidity increases

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21. The advantage of dry compression is that

All of the above

It permits higher speeds to be used

It permits complete evaporation in the evaporator

It results in high volumetric and mechanical efficiency

22. Air refrigeration operates on

Reversed Carnot cycle

Carnot cycle

Rankine’s cycle

Brayton cycle

23. 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)]

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

High

Small

Anything

Equal

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

Carbon dioxide

Ammonia

Sulphur dioxide

R-12

26. 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

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

Will be lower

Will remain unaffected

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

Flooded

None of these

Dry

DX coil

28. The sub-cooling in a refrigeration cycle

Increases C.O.P.

Does not alter C.O.P.

Decreases C.O.P.

None of these

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

Mean radiant temperature

Dew point temperature

Effective temperature

None of these

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

Room sensible heat load only

None of the above

Both room sensible heat and latent heat loads

Room latent heat load only

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31. The specific humidity during dehumidification process

Decreases

None of these

Remains constant

Increases

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

Higher than

None of these

Lower than

Same as

33. Superheating in a refrigeration cycle

Decreases C.O.P

Other factors decide C.O.P

C.O.P remains unaltered

Increases C.O.P

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

Compression

Absorption

Indirect

Direct

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

Compressor and evaporator

Expansion valve and evaporator

Compressor and condenser

Condenser and expansion valve

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

Before passing through the condenser

Before entering the compressor

After passing through the condenser

After passing through the expansion or throttle valve

37. Vapour compression refrigeration is somewhat like

Reversed Carnot cycle

Rankine’s cycle

None of the above

Carnot cycle

38. Refrigeration in aeroplanes usually employs the following refrigerant

CO2

Air

Freon-22

Freon-11

39. Moisture in Freon refrigeration system causes

Corrosion of whole system

Ineffective refrigeration

Freezing automatic regulating valve

High power consumption

40. 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

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

Evaporation of the refrigerant liquid

Metering of the refrigerant liquid

Compression of the refrigerant vapour

Condensation of the refrigerant vapour

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

Enthalpy increase in compressor

All of the above

Work done by compressor

Heat of compression

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

Freon-12

CO2

Freon-22

NH3

44. During cooling and dehumidification, dry bulb temperature

None of these

Decreases

Increases

Remains constant

45. The relative coefficient of performance is

Theoretical COP/actual COP

Actual COP × theoretical COP

Actual COP/theoretical COP

None of these

Refrigeration & Air-Conditioning Practice Set-4

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