Refrigeration & Air-Conditioning Practice Set-4

Page 1 of 5

1. Moisture in Freon refrigeration system causes

Corrosion of whole system

Ineffective refrigeration

High power consumption

Freezing automatic regulating valve

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

Saturated liquid

Dry saturated vapour

Superheated vapour

Wet vapour

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

More or less depending on ambient conditions

More

Same

Less

4. Vapour compression refrigeration is somewhat like

Reversed Carnot cycle

None of the above

Rankine’s cycle

Carnot cycle

5. The sub-cooling in a refrigeration cycle

Increases C.O.P.

None of these

Decreases C.O.P.

Does not alter C.O.P.

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

Freon-12

NH3

Freon-22

CO2

7. The relative coefficient of performance is

Actual COP × theoretical COP

None of these

Actual COP/theoretical COP

Theoretical COP/actual COP

8. 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)/(td₂ - td₃)

(td₂ - td₃)/(td₃ - td₁)

(td₃ - td₁)/(td₃ - td₂)

9. The specific humidity during dehumidification process

None of these

Remains constant

Increases

Decreases

10. The superheating in a refrigeration cycle

None of these

Decreases C.O.P.

Increases C.O.P.

Does not alter C.O.P.

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11. Ammonia absorption refrigeration cycle requires

Very little work input

Zero work input

Maximum work input

Nearly same work input as for vapour compression cycle

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

Ammonia

R-12

Sulphur dioxide

Carbon dioxide

13. During cooling and dehumidification, dry bulb temperature

None of these

Increases

Decreases

Remains constant

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

Water at 0°C

Solid and dry ice

Mixture of ice and water under equilibrium conditions

Ice at 4°C

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

Heat of compression

Work done by compressor

Enthalpy increase in compressor

All of the above

16. 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

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

Condensation of the refrigerant vapour

Evaporation of the refrigerant liquid

Compression of the refrigerant vapour

Metering of the refrigerant liquid

18. Refrigeration in aeroplanes usually employs the following refrigerant

Freon-22

Air

CO2

Freon-11

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

Sulphur dioxide

R-12

Ammonia

Carbon dioxide

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

Compression

Direct

Absorption

Indirect

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

Remain unaffected

Decrease

May increase or decrease depending on the type of refrigerant used

Increase

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

Absolute

Relative

Specific

None of these

23. Superheating in a refrigeration cycle

C.O.P remains unaltered

Increases C.O.P

Other factors decide C.O.P

Decreases C.O.P

24. The Freon group of refrigerants are

Hydrocarbon refrigerants

Inorganic refrigerants

Zoetrope refrigerants

Halocarbon refrigerants

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

Sulphur sticks

Soap and water

Halide torch

All of these

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

Expansion valve and evaporator

Condenser and expansion valve

Compressor and condenser

Compressor and evaporator

27. The advantage of dry compression is that

All of the above

It results in high volumetric and mechanical efficiency

It permits complete evaporation in the evaporator

It permits higher speeds to be used

28. 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

29. Which of the following statement is correct?

All of these

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

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

The constant enthalpy lines are also constant wet bulb temperature lines

30. During sensible cooling,

Specific humidity increases

Relative humidity remains constant

Partial pressure of vapour remains constant

Wet bulb temperature increases

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31. 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)

μ/[1 - (1 - μ) (Ps/Pb)]

None of these

32. The specific humidity during heating and humidification process.

Increases

Decreases

Remains constant

None of these

33. 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 60% RH

20°C DBT and 50% RH

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

None of these

DX coil

Dry

Flooded

35. 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

Dew point temperature

Mean radiant temperature

Effective temperature

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

0.2

5

6

1.2

37. 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)

(h2 - hA)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

(hA - h1)/ (h2 - h1)

38. Air conditioning means

Cooling

Dehumidifying

Heating

All of these

39. 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

1 kW

2 kW

3 kW

4 kW

40. 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

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

There is no such consideration

Less than 2 kg

More than or equal to 3.65 kg

More than 10 kg

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

Higher than

Same as

Lower than

None of these

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

High

Equal

Anything

Small

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

After passing through the condenser

After passing through the expansion or throttle valve

Before passing through the condenser

Before entering the compressor

45. Air refrigeration operates on

Brayton cycle

Carnot cycle

Rankine’s cycle

Reversed Carnot cycle

Refrigeration & Air-Conditioning Practice Set-4

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