Refrigeration & Air-Conditioning Practice Set-4

Page 1 of 5

1. During sensible cooling,

Wet bulb temperature increases

Partial pressure of vapour remains constant

Relative humidity remains constant

Specific humidity increases

2. 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 - h1)/ (h2 - h1)

(hA - h2)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

3. During cooling and dehumidification, dry bulb temperature

None of these

Remains constant

Decreases

Increases

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

R-12

Carbon dioxide

Ammonia

Sulphur dioxide

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

More

Less

Same

More or less depending on ambient conditions

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

Dry saturated vapour

Saturated liquid

Wet vapour

Superheated vapour

7. 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

1 kW

3 kW

8. Vapour compression refrigeration is somewhat like

Reversed Carnot cycle

None of the above

Carnot cycle

Rankine’s cycle

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

Sulphur dioxide

Ammonia

R-12

Carbon dioxide

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

Freon-12

NH3

Freon-22

CO2

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11. Superheating in a refrigeration cycle

Increases C.O.P

C.O.P remains unaltered

Decreases C.O.P

Other factors decide C.O.P

12. 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

13. The Freon group of refrigerants are

Halocarbon refrigerants

Inorganic refrigerants

Hydrocarbon refrigerants

Zoetrope refrigerants

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

None of these

Mean radiant temperature

Effective temperature

Dew point temperature

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

Expansion valve and evaporator

Compressor and evaporator

Condenser and expansion valve

Compressor and condenser

16. Air conditioning means

Dehumidifying

Cooling

All of these

Heating

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

Indirect

Direct

Compression

Absorption

18. The specific humidity during dehumidification process

Decreases

Remains constant

None of these

Increases

19. 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

20. 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

Will be lower

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

Will be higher

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

Specific

None of these

Relative

Absolute

22. Refrigeration in aeroplanes usually employs the following refrigerant

Air

Freon-22

Freon-11

CO2

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

Equal

Anything

Small

High

24. Moisture in Freon refrigeration system causes

Corrosion of whole system

Ineffective refrigeration

High power consumption

Freezing automatic regulating valve

25. Ammonia absorption refrigeration cycle requires

Zero work input

Very little work input

Nearly same work input as for vapour compression cycle

Maximum work input

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

Halide torch

Soap and water

Sulphur sticks

All of these

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

Dry

None of these

DX coil

Flooded

28. 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

All of these

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

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

20°C DBT and 60% RH

26°C DBT and 60% RH

26°C DBT and 50% RH

20°C DBT and 50% RH

30. 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

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

None of these

Same as

Lower than

Higher than

32. 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)/(td₂ - td₃)

(td₃ - td₁)/(td₃ - td₂)

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)

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

0.622 Pv / (Pb - Pv)

None of these

μ/[1 - (1 - μ) (Ps/Pb)]

34. The superheating in a refrigeration cycle

Decreases C.O.P.

Does not alter C.O.P.

None of these

Increases C.O.P.

35. The specific humidity during heating and humidification process.

Decreases

Remains constant

Increases

None of these

36. The advantage of dry compression is that

It results in high volumetric and mechanical efficiency

It permits higher speeds to be used

It permits complete evaporation in the evaporator

All of the above

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

Ice at 4°C

Water at 0°C

Mixture of ice and water under equilibrium conditions

Solid and dry ice

38. 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

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

Room latent heat load only

None of the above

Room sensible heat load only

Both room sensible heat and latent heat loads

40. 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

5

1.2

6

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41. Air refrigeration operates on

Carnot cycle

Reversed Carnot cycle

Brayton cycle

Rankine’s cycle

42. The sub-cooling in a refrigeration cycle

Does not alter C.O.P.

Increases C.O.P.

None of these

Decreases C.O.P.

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

Compression of the refrigerant vapour

Evaporation of the refrigerant liquid

Metering of the refrigerant liquid

Condensation of the refrigerant vapour

44. The relative coefficient of performance is

Actual COP/theoretical COP

Actual COP × theoretical COP

None of these

Theoretical COP/actual COP

45. 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

Refrigeration & Air-Conditioning Practice Set-4

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