Refrigeration & Air-Conditioning Practice Set-4

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1. The relative coefficient of performance is

None of these

Theoretical COP/actual COP

Actual COP × theoretical COP

Actual COP/theoretical COP

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)

(hA - h2)/ (h1 - h2)

(h2 - hA)/ (h1 - h2)

(hA - h1)/ (h2 - h1)

(h1 - h2)/ (hA - h2)

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

Compressor and condenser

Expansion valve and evaporator

Condenser and expansion valve

Compressor and evaporator

4. 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

More than or equal to 3.65 kg

Less than 2 kg

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

Water at 0°C

Ice at 4°C

Solid and dry ice

Mixture of ice and water under equilibrium conditions

6. During sensible cooling,

Relative humidity remains constant

Specific humidity increases

Wet bulb temperature increases

Partial pressure of vapour remains constant

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

Ammonia

R-12

Carbon dioxide

Sulphur dioxide

8. 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

9. Superheating in a refrigeration cycle

Increases C.O.P

C.O.P remains unaltered

Decreases C.O.P

Other factors decide C.O.P

10. During cooling and dehumidification, dry bulb temperature

None of these

Decreases

Increases

Remains constant

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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

Dew point temperature

None of these

Mean radiant temperature

Effective temperature

12. The condensing pressure due to the presence of non-condensable gases, as compared to that actually required for condensing temperatures without non-condensable gases,

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

Will be lower

Will be higher

Will remain unaffected

13. 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

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

CO2

NH3

Freon-22

Freon-12

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

All of these

Halide torch

Soap and water

Sulphur sticks

16. The superheating in a refrigeration cycle

Decreases C.O.P.

None of these

Increases C.O.P.

Does not alter C.O.P.

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

Increase

Decrease

Remain unaffected

May increase or decrease depending on the type of refrigerant used

18. Which of the following statement is correct?

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

The constant enthalpy lines are also constant wet bulb temperature lines

19. 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

20. The advantage of dry compression is that

It permits complete evaporation in the evaporator

It results in high volumetric and mechanical efficiency

All of the above

It permits higher speeds to be used

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21. Vapour compression refrigeration is somewhat like

Reversed Carnot cycle

None of the above

Rankine’s cycle

Carnot cycle

22. Air refrigeration operates on

Brayton cycle

Carnot cycle

Reversed Carnot cycle

Rankine’s cycle

23. 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

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

Which lies between the dry bulb and wet bulb temperatures of the incoming stream

Of adiabatic saturation of incoming stream

24. Air conditioning means

All of these

Heating

Dehumidifying

Cooling

25. Ammonia absorption refrigeration cycle requires

Zero work input

Maximum work input

Very little work input

Nearly same work input as for vapour compression cycle

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

Superheated vapour

Wet vapour

Saturated liquid

Dry saturated vapour

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

Relative

None of these

Specific

Absolute

28. Moisture in Freon refrigeration system causes

Freezing automatic regulating valve

Corrosion of whole system

High power consumption

Ineffective refrigeration

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

More

Same

More or less depending on ambient conditions

Less

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

Enthalpy increase in compressor

Work done by compressor

All of the above

Heat of compression

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

None of these

Higher than

Lower than

Same as

32. 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

μ/[1 - (1 - μ) (Ps/Pb)]

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

0.622 Pv / (Pb - Pv)

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

Ammonia

R-12

Carbon dioxide

Sulphur dioxide

34. 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)

(td₃ - td₁)/(td₂ - td₃)

(td₂ - td₃)/(td₃ - td₁)

(td₃ - td₂)/(td₃ - td₁)

35. The Freon group of refrigerants are

Inorganic refrigerants

Hydrocarbon refrigerants

Halocarbon refrigerants

Zoetrope refrigerants

36. Refrigeration in aeroplanes usually employs the following refrigerant

Freon-11

Freon-22

CO2

Air

37. The specific humidity during heating and humidification process.

Decreases

Increases

None of these

Remains constant

38. The specific humidity during dehumidification process

Remains constant

None of these

Decreases

Increases

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

Indirect

Absorption

Direct

Compression

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

20°C DBT and 50% RH

20°C DBT and 60% RH

26°C DBT and 60% RH

26°C DBT and 50% RH

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41. 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

0.2

1.2

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

Small

Equal

Anything

High

43. The sub-cooling in a refrigeration cycle

None of these

Increases C.O.P.

Decreases C.O.P.

Does not alter C.O.P.

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

After passing through the condenser

Before entering the compressor

After passing through the expansion or throttle valve

Before passing through the condenser

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

Dry

Flooded

None of these

DX coil

Refrigeration & Air-Conditioning Practice Set-4

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