Refrigeration & Air-Conditioning Practice Set-4

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

Small

Anything

High

Equal

2. The relative coefficient of performance is

Actual COP/theoretical COP

None of these

Theoretical COP/actual COP

Actual COP × theoretical COP

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

Evaporation of the refrigerant liquid

Compression of the refrigerant vapour

Metering of the refrigerant liquid

Condensation of the refrigerant vapour

4. 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

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

None of these

Specific

Absolute

Relative

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

More than or equal to 3.65 kg

Less than 2 kg

There is no such consideration

More than 10 kg

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

2 kW

1 kW

3 kW

4 kW

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

Heat of compression

Work done by compressor

All of the above

Enthalpy increase in compressor

9. During sensible cooling,

Wet bulb temperature increases

Partial pressure of vapour remains constant

Specific humidity increases

Relative humidity remains constant

10. 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)]

0.622 Pv / (Pb - Pv)

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

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11. Moisture in Freon refrigeration system causes

High power consumption

Ineffective refrigeration

Freezing automatic regulating valve

Corrosion of whole system

12. The specific humidity during dehumidification process

Decreases

Remains constant

Increases

None of these

13. Refrigeration in aeroplanes usually employs the following refrigerant

Freon-11

CO2

Air

Freon-22

14. Vapour compression refrigeration is somewhat like

Rankine’s cycle

Carnot cycle

Reversed Carnot cycle

None of the above

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

Effective temperature

Mean radiant temperature

Dew point temperature

None of these

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

Compression

Direct

Absorption

Indirect

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

Compressor and condenser

Condenser and expansion valve

Expansion valve and evaporator

Compressor and evaporator

18. 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 - td₂)/(td₃ - td₁)

(td₃ - td₁)/(td₂ - td₃)

(td₂ - td₃)/(td₃ - td₁)

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

Sulphur dioxide

R-12

Ammonia

Carbon dioxide

20. 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

1.2

0.2

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21. 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 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

22. 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

Will be higher

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

Will remain unaffected

23. The superheating in a refrigeration cycle

Does not alter C.O.P.

Increases C.O.P.

None of these

Decreases C.O.P.

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

Superheated vapour

Dry saturated vapour

Wet vapour

Saturated liquid

25. The specific humidity during heating and humidification process.

Decreases

Remains constant

None of these

Increases

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

DX coil

Flooded

Dry

None of these

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

Ammonia

Carbon dioxide

Sulphur dioxide

R-12

28. The sub-cooling in a refrigeration cycle

Decreases C.O.P.

None of these

Increases C.O.P.

Does not alter C.O.P.

29. Superheating in a refrigeration cycle

Increases C.O.P

Other factors decide C.O.P

C.O.P remains unaltered

Decreases C.O.P

30. 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

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

None of these

Higher than

Same as

Lower than

32. The Freon group of refrigerants are

Hydrocarbon refrigerants

Halocarbon refrigerants

Inorganic refrigerants

Zoetrope refrigerants

33. During cooling and dehumidification, dry bulb temperature

Increases

Decreases

Remains constant

None of these

34. Ammonia absorption refrigeration cycle requires

Very little work input

Zero work input

Maximum work input

Nearly same work input as for vapour compression cycle

35. Air conditioning means

All of these

Heating

Dehumidifying

Cooling

36. 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

37. 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

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

Sulphur sticks

Halide torch

Soap and water

All of these

39. Air refrigeration operates on

Rankine’s cycle

Reversed Carnot cycle

Carnot cycle

Brayton cycle

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

NH3

CO2

Freon-22

Freon-12

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41. Which of the following statement is correct?

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

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

42. 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

43. 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)

(h1 - h2)/ (hA - h2)

(hA - h2)/ (h1 - h2)

(h2 - hA)/ (h1 - h2)

(hA - h1)/ (h2 - h1)

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

Mixture of ice and water under equilibrium conditions

Ice at 4°C

Water at 0°C

Solid and dry ice

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

Room latent heat load only

Room sensible heat load only

Both room sensible heat and latent heat loads

None of the above

Refrigeration & Air-Conditioning Practice Set-4

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