Refrigeration & Air-Conditioning Practice Set-4

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1. The advantage of dry compression is that

All of the above

It permits complete evaporation in the evaporator

It results in high volumetric and mechanical efficiency

It permits higher speeds to be used

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. Air conditioning means

All of these

Cooling

Heating

Dehumidifying

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

Evaporation of the refrigerant liquid

Condensation of the refrigerant vapour

Metering of the refrigerant liquid

Compression of the refrigerant vapour

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

20°C DBT and 60% RH

26°C DBT and 60% RH

20°C DBT and 50% RH

26°C DBT and 50% RH

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

Expansion valve and evaporator

Condenser and expansion valve

Compressor and evaporator

Compressor and condenser

7. Air refrigeration operates on

Rankine’s cycle

Carnot cycle

Reversed Carnot cycle

Brayton cycle

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

None of these

Dry

Flooded

DX coil

9. 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

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

None of these

Higher than

Lower than

Same as

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

Superheated vapour

Wet vapour

Dry saturated vapour

Saturated liquid

12. 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

13. The relative coefficient of performance is

Actual COP × theoretical COP

None of these

Theoretical COP/actual COP

Actual COP/theoretical COP

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

Carbon dioxide

Sulphur dioxide

Ammonia

R-12

15. During cooling and dehumidification, dry bulb temperature

Increases

None of these

Remains constant

Decreases

16. Vapour compression refrigeration is somewhat like

None of the above

Reversed Carnot cycle

Carnot cycle

Rankine’s cycle

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

Freon-12

CO2

NH3

Freon-22

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

More or less depending on ambient conditions

Less

Same

More

19. The superheating in a refrigeration cycle

None of these

Decreases C.O.P.

Does not alter C.O.P.

Increases C.O.P.

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

Increase

Remain unaffected

May increase or decrease depending on the type of refrigerant used

Decrease

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

Halide torch

Soap and water

All of these

Sulphur sticks

22. Refrigeration in aeroplanes usually employs the following refrigerant

Freon-11

Air

Freon-22

CO2

23. Moisture in Freon refrigeration system causes

High power consumption

Corrosion of whole system

Freezing automatic regulating valve

Ineffective refrigeration

24. 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

Mean radiant temperature

Dew point temperature

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

Less than 2 kg

More than or equal to 3.65 kg

More than 10 kg

There is no such consideration

26. 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

27. 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

1.2

6

0.2

28. Which of the following statement is correct?

The constant enthalpy lines are also constant wet bulb temperature lines

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

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

All of these

29. 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 remain unaffected

Will be lower

30. 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 - td₁)/(td₃ - td₂)

(td₂ - td₃)/(td₃ - td₁)

(td₃ - td₂)/(td₃ - td₁)

(td₃ - td₁)/(td₂ - td₃)

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31. 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

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

None of these

Absolute

Specific

Relative

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

Ice at 4°C

Solid and dry ice

Mixture of ice and water under equilibrium conditions

Water at 0°C

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

Ammonia

Carbon dioxide

Sulphur dioxide

R-12

35. During sensible cooling,

Partial pressure of vapour remains constant

Relative humidity remains constant

Specific humidity increases

Wet bulb temperature increases

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

Compression

Indirect

Direct

Absorption

37. Ammonia absorption refrigeration cycle requires

Maximum work input

Nearly same work input as for vapour compression cycle

Very little work input

Zero work input

38. In order to cool and dehumidify a stream of moist air, it must be passed over the coil at a temperature

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

Which lies between the wet bulb and dew point temperatures of the incoming stream

39. The specific humidity during dehumidification process

Remains constant

Decreases

Increases

None of these

40. Superheating in a refrigeration cycle

C.O.P remains unaltered

Other factors decide C.O.P

Increases C.O.P

Decreases C.O.P

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41. The Freon group of refrigerants are

Halocarbon refrigerants

Zoetrope refrigerants

Inorganic refrigerants

Hydrocarbon refrigerants

42. 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

3 kW

4 kW

43. The specific humidity during heating and humidification process.

None of these

Increases

Remains constant

Decreases

44. The sub-cooling in a refrigeration cycle

Does not alter C.O.P.

Decreases C.O.P.

Increases C.O.P.

None of these

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

Anything

Small

High

Equal

Refrigeration & Air-Conditioning Practice Set-4

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