Refrigeration & Air-Conditioning Practice Set-4

June 7, 2021

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1. Refrigeration in aeroplanes usually employs the following refrigerant

Freon-22

Air

CO2

Freon-11

2. 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

1.2

0.2

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

Before passing through the condenser

Before entering the compressor

After passing through the expansion or throttle valve

After passing through the condenser

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

Decrease

Remain unaffected

May increase or decrease depending on the type of refrigerant used

Increase

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

Carbon dioxide

R-12

Sulphur dioxide

Ammonia

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

Lower than

Same as

Higher than

None of these

7. 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 remain unaffected

Will be higher

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

8. Vapour compression refrigeration is somewhat like

None of the above

Carnot cycle

Reversed Carnot cycle

Rankine’s cycle

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

Compression of the refrigerant vapour

Condensation of the refrigerant vapour

Evaporation of the refrigerant liquid

Metering of the refrigerant liquid

10. The specific humidity during dehumidification process

Remains constant

Increases

Decreases

None of these

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11. 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)

μ/[1 - (1 - μ) (Ps/Pb)]

0.622 Pv / (Pb - Pv)

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

None of these

12. Moisture in Freon refrigeration system causes

Corrosion of whole system

High power consumption

Ineffective refrigeration

Freezing automatic regulating valve

13. 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

3 kW

1 kW

4 kW

14. During sensible cooling,

Partial pressure of vapour remains constant

Wet bulb temperature increases

Relative humidity remains constant

Specific humidity increases

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

Carbon dioxide

R-12

Sulphur dioxide

Ammonia

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

Dry

Flooded

DX coil

None of these

17. The advantage of dry compression is that

All of the above

It permits higher speeds to be used

It results in high volumetric and mechanical efficiency

It permits complete evaporation in the evaporator

18. Superheating in a refrigeration cycle

Decreases C.O.P

C.O.P remains unaltered

Other factors decide C.O.P

Increases C.O.P

19. 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)

(h1 - h2)/ (hA - h2)

(hA - h1)/ (h2 - h1)

(hA - h2)/ (h1 - h2)

20. The superheating in a refrigeration cycle

Increases C.O.P.

Decreases C.O.P.

Does not alter C.O.P.

None of these

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

Absolute

Specific

Relative

None of these

22. Air refrigeration operates on

Reversed Carnot cycle

Brayton cycle

Carnot cycle

Rankine’s cycle

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

NH3

Freon-22

CO2

Freon-12

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

Ice at 4°C

Water at 0°C

Solid and dry ice

Mixture of ice and water under equilibrium conditions

25. The Freon group of refrigerants are

Halocarbon refrigerants

Hydrocarbon refrigerants

Inorganic refrigerants

Zoetrope refrigerants

26. Ammonia absorption refrigeration cycle requires

Very little work input

Maximum work input

Nearly same work input as for vapour compression cycle

Zero work input

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

26°C DBT and 60% RH

20°C DBT and 50% RH

20°C DBT and 60% RH

26°C DBT and 50% RH

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

Anything

Small

High

Equal

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

Compressor and condenser

Condenser and expansion valve

Expansion valve and evaporator

Compressor and evaporator

30. 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

The constant enthalpy lines are also constant wet bulb temperature lines

All of these

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

Enthalpy increase in compressor

All of the above

Work done by compressor

Heat of compression

32. The relative coefficient of performance is

Actual COP/theoretical COP

Actual COP × theoretical COP

None of these

Theoretical COP/actual COP

33. 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 is lower than the dew point temperature of the incoming stream

Of adiabatic saturation of incoming stream

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

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

Mean radiant temperature

Dew point temperature

Effective temperature

None of these

35. Air conditioning means

Heating

All of these

Cooling

Dehumidifying

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

Less

Same

More or less depending on ambient conditions

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

All of these

Halide torch

Soap and water

Sulphur sticks

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

Indirect

Absorption

Direct

Compression

39. The specific humidity during heating and humidification process.

Increases

None of these

Decreases

Remains constant

40. During cooling and dehumidification, dry bulb temperature

None of these

Remains constant

Increases

Decreases

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

Wet vapour

Dry saturated vapour

Superheated vapour

Saturated liquid

42. The sub-cooling in a refrigeration cycle

Decreases C.O.P.

Increases C.O.P.

Does not alter C.O.P.

None of these

43. 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)/(td₂ - td₃)

(td₂ - td₃)/(td₃ - td₁)

(td₃ - td₁)/(td₃ - td₂)

(td₃ - td₂)/(td₃ - td₁)

44. 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

More than 10 kg

Less than 2 kg

There is no such consideration

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

None of the above

Room latent heat load only

Both room sensible heat and latent heat loads

Room sensible heat load only

Refrigeration & Air-Conditioning Practice Set-4

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