Refrigeration & Air-Conditioning Practice Set-4

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1. Moisture in Freon refrigeration system causes

Ineffective refrigeration

High power consumption

Corrosion of whole system

Freezing automatic regulating valve

2. Superheating in a refrigeration cycle

Other factors decide C.O.P

Increases C.O.P

C.O.P remains unaltered

Decreases C.O.P

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

Room sensible heat load only

Room latent heat load only

Both room sensible heat and latent heat loads

None of the above

4. Refrigeration in aeroplanes usually employs the following refrigerant

Freon-22

Freon-11

CO2

Air

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

Sulphur sticks

All of these

Soap and water

Halide torch

6. 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

2 kW

4 kW

1 kW

3 kW

7. 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

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

Ammonia

Carbon dioxide

R-12

Sulphur dioxide

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

Condensation of the refrigerant vapour

Compression of the refrigerant vapour

Metering of the refrigerant liquid

Evaporation of the refrigerant liquid

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

Lower than

None of these

Same as

Higher than

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11. 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 - h2)/ (h1 - h2)

(hA - h1)/ (h2 - h1)

(h1 - h2)/ (hA - h2)

(h2 - hA)/ (h1 - h2)

12. The specific humidity during heating and humidification process.

Remains constant

None of these

Increases

Decreases

13. Air conditioning means

Dehumidifying

Cooling

All of these

Heating

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

Saturated liquid

Wet vapour

Superheated vapour

Dry saturated vapour

15. The Freon group of refrigerants are

Inorganic refrigerants

Hydrocarbon refrigerants

Zoetrope refrigerants

Halocarbon refrigerants

16. 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 remain unaffected

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

Will be higher

Will be lower

17. 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

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

Dry

Flooded

DX coil

None of these

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

More or less depending on ambient conditions

Same

Less

More

20. Air refrigeration operates on

Reversed Carnot cycle

Brayton cycle

Rankine’s cycle

Carnot cycle

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21. The specific humidity during dehumidification process

Increases

Decreases

None of these

Remains constant

22. 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

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

Of adiabatic saturation of incoming stream

23. The advantage of dry compression is that

All of the above

It permits higher speeds to be used

It results in high volumetric and mechanical efficiency

It permits complete evaporation in the evaporator

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

Enthalpy increase in compressor

Work done by compressor

Heat of compression

All of the above

25. During cooling and dehumidification, dry bulb temperature

Increases

None of these

Remains constant

Decreases

26. The sub-cooling in a refrigeration cycle

Increases C.O.P.

None of these

Decreases C.O.P.

Does not alter C.O.P.

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

Before entering the compressor

Before passing through the condenser

After passing through the condenser

After passing through the expansion or throttle valve

28. 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

None of these

Effective temperature

29. 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 - td₂)/(td₃ - td₁)

(td₃ - td₁)/(td₃ - td₂)

(td₃ - td₁)/(td₂ - td₃)

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

Freon-22

Freon-12

NH3

CO2

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31. The superheating in a refrigeration cycle

Increases C.O.P.

Does not alter C.O.P.

None of these

Decreases C.O.P.

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

Absorption

Indirect

Direct

Compression

33. 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)]

μ/[1 - (1 - μ) (Ps/Pb)]

0.622 Pv / (Pb - Pv)

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

Ice at 4°C

Water at 0°C

Solid and dry ice

Mixture of ice and water under equilibrium conditions

35. During sensible cooling,

Specific humidity increases

Partial pressure of vapour remains constant

Wet bulb temperature increases

Relative humidity remains constant

36. 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

37. 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

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

Anything

High

Equal

Small

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

Compressor and evaporator

Condenser and expansion valve

Expansion valve and evaporator

Compressor and condenser

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

Sulphur dioxide

Carbon dioxide

Ammonia

R-12

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

Decrease

Remain unaffected

May increase or decrease depending on the type of refrigerant used

Increase

42. Vapour compression refrigeration is somewhat like

Reversed Carnot cycle

Rankine’s cycle

None of the above

Carnot cycle

43. Ammonia absorption refrigeration cycle requires

Maximum work input

Very little work input

Zero work input

Nearly same work input as for vapour compression cycle

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

Absolute

Specific

Relative

None of these

45. The relative coefficient of performance is

Actual COP × theoretical COP

Actual COP/theoretical COP

Theoretical COP/actual COP

None of these

Refrigeration & Air-Conditioning Practice Set-4

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