Refrigeration & Air-Conditioning Practice Set-4

Page 1 of 5

1. Air conditioning means

All of these

Dehumidifying

Heating

Cooling

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

All of the above

Enthalpy increase in compressor

Heat of compression

Work done by compressor

3. Vapour compression refrigeration is somewhat like

None of the above

Carnot cycle

Reversed Carnot cycle

Rankine’s cycle

4. 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)

5. 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)

0.622 Pv / (Pb - Pv)

μ/[1 - (1 - μ) (Ps/Pb)]

None of these

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

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

Remain unaffected

Increase

Decrease

7. During sensible cooling,

Partial pressure of vapour remains constant

Relative humidity remains constant

Specific humidity increases

Wet bulb temperature increases

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

Direct

Absorption

Compression

Indirect

9. Air refrigeration operates on

Reversed Carnot cycle

Carnot cycle

Brayton cycle

Rankine’s cycle

10. Superheating in a refrigeration cycle

C.O.P remains unaltered

Decreases C.O.P

Other factors decide C.O.P

Increases C.O.P

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

Effective temperature

None of these

Dew point temperature

Mean radiant temperature

12. The sub-cooling in a refrigeration cycle

Decreases C.O.P.

Does not alter C.O.P.

Increases C.O.P.

None of these

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

Mixture of ice and water under equilibrium conditions

Water at 0°C

Solid and dry ice

Ice at 4°C

14. 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

0.2

1.2

5

6

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

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

Will be higher

Will remain unaffected

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

R-12

Sulphur dioxide

Carbon dioxide

Ammonia

17. Which of the following statement is correct?

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

All of these

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

The constant enthalpy lines are also constant wet bulb temperature lines

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

Ammonia

R-12

Sulphur dioxide

Carbon dioxide

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

Wet vapour

Superheated vapour

Dry saturated vapour

Saturated liquid

20. The relative coefficient of performance is

None of these

Theoretical COP/actual COP

Actual COP/theoretical COP

Actual COP × theoretical COP

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

CO2

NH3

Freon-22

Freon-12

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

Relative

Absolute

Specific

None of these

23. Moisture in Freon refrigeration system causes

Corrosion of whole system

High power consumption

Freezing automatic regulating valve

Ineffective refrigeration

24. 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

25. The superheating in a refrigeration cycle

Decreases C.O.P.

Does not alter C.O.P.

Increases C.O.P.

None of these

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

Higher than

Same as

Lower than

None of these

27. 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 wet bulb and dew point temperatures 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 is lower than the dew point temperature of the incoming stream

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

None of the above

Room latent heat load only

Room sensible heat load only

Both room sensible heat and latent heat loads

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

Dry

None of these

Flooded

DX coil

30. 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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31. The alignment circle is marked on the psychrometric chart at

26°C DBT and 50% RH

26°C DBT and 60% RH

20°C DBT and 50% RH

20°C DBT and 60% RH

32. The Freon group of refrigerants are

Inorganic refrigerants

Halocarbon refrigerants

Zoetrope refrigerants

Hydrocarbon refrigerants

33. Ammonia absorption refrigeration cycle requires

Very little work input

Nearly same work input as for vapour compression cycle

Zero work input

Maximum work input

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

Before passing through the condenser

After passing through the condenser

After passing through the expansion or throttle valve

Before entering the compressor

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

Compressor and evaporator

Condenser and expansion valve

Compressor and condenser

Expansion valve and evaporator

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

Small

Anything

High

Equal

37. During cooling and dehumidification, dry bulb temperature

Increases

Remains constant

Decreases

None of these

38. 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

39. 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)

(h1 - h2)/ (hA - h2)

(h2 - hA)/ (h1 - h2)

(hA - h2)/ (h1 - h2)

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

All of these

Halide torch

Soap and water

Sulphur sticks

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41. 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

1 kW

4 kW

3 kW

42. The specific humidity during heating and humidification process.

Remains constant

Increases

None of these

Decreases

43. 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

44. The specific humidity during dehumidification process

Decreases

None of these

Increases

Remains constant

45. Refrigeration in aeroplanes usually employs the following refrigerant

CO2

Freon-22

Freon-11

Air

Refrigeration & Air-Conditioning Practice Set-4

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