Refrigeration & Air-Conditioning Practice Set-4

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

CO2

NH3

Freon-12

Freon-22

2. The advantage of dry compression is that

It permits complete evaporation in the evaporator

It results in high volumetric and mechanical efficiency

It permits higher speeds to be used

All of the above

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

None of these

Dry

Flooded

DX coil

4. 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)

(hA - h1)/ (h2 - h1)

(h2 - hA)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

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

Evaporation of the refrigerant liquid

Condensation of the refrigerant vapour

Compression of the refrigerant vapour

Metering of the refrigerant liquid

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

After passing through the expansion or throttle valve

Before passing through the condenser

Before entering the compressor

After passing through the condenser

7. The specific humidity during heating and humidification process.

None of these

Remains constant

Increases

Decreases

8. 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

9. Which of the following statement is correct?

The constant enthalpy lines are also constant wet bulb temperature lines

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

10. Moisture in Freon refrigeration system causes

Corrosion of whole system

Ineffective refrigeration

Freezing automatic regulating valve

High power consumption

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

All of these

Soap and water

Halide torch

Sulphur sticks

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

26°C DBT and 50% RH

20°C DBT and 50% RH

20°C DBT and 60% RH

26°C DBT and 60% RH

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

Condenser and expansion valve

Compressor and evaporator

Expansion valve and evaporator

Compressor and condenser

14. 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

4 kW

3 kW

15. The superheating in a refrigeration cycle

Does not alter C.O.P.

None of these

Increases C.O.P.

Decreases C.O.P.

16. The relative coefficient of performance is

Theoretical COP/actual COP

Actual COP/theoretical COP

Actual COP × theoretical COP

None of these

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

Relative

Specific

Absolute

None of these

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

Higher than

Lower than

None of these

Same as

19. 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

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

R-12

Sulphur dioxide

Ammonia

Carbon dioxide

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21. During sensible cooling,

Partial pressure of vapour remains constant

Specific humidity increases

Wet bulb temperature increases

Relative humidity remains constant

22. Ammonia absorption refrigeration cycle requires

Maximum work input

Nearly same work input as for vapour compression cycle

Zero work input

Very little work input

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

Dry saturated vapour

Saturated liquid

Superheated vapour

Wet vapour

24. 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 remain unaffected

Will be lower

Will be higher

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

25. The specific humidity during dehumidification process

None of these

Increases

Remains constant

Decreases

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

Small

High

Anything

Equal

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

Mixture of ice and water under equilibrium conditions

Water at 0°C

Ice at 4°C

Solid and dry ice

28. The Freon group of refrigerants are

Hydrocarbon refrigerants

Halocarbon refrigerants

Zoetrope refrigerants

Inorganic refrigerants

29. 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

1.2

5

6

30. 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

Effective temperature

Dew point temperature

Mean radiant temperature

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31. The sub-cooling in a refrigeration cycle

Increases C.O.P.

Decreases C.O.P.

None of these

Does not alter C.O.P.

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

Compression

Direct

Indirect

Absorption

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

Room latent heat load only

Both room sensible heat and latent heat loads

None of the above

Room sensible heat load only

34. 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

There is no such consideration

More than 10 kg

35. 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)

0.622 Pv / (Pb - Pv)

None of these

μ/[1 - (1 - μ) (Ps/Pb)]

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

36. Air refrigeration operates on

Rankine’s cycle

Carnot cycle

Reversed Carnot cycle

Brayton cycle

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

May increase or decrease depending on the type of refrigerant used

Increase

Decrease

Remain unaffected

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

More or less depending on ambient conditions

More

Less

Same

39. 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)

(td₂ - td₃)/(td₃ - td₁)

(td₃ - td₁)/(td₂ - td₃)

(td₃ - td₂)/(td₃ - td₁)

(td₃ - td₁)/(td₃ - td₂)

40. Air conditioning means

Cooling

Heating

Dehumidifying

All of these

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

Sulphur dioxide

Carbon dioxide

Ammonia

R-12

42. Superheating in a refrigeration cycle

Increases C.O.P

Other factors decide C.O.P

C.O.P remains unaltered

Decreases C.O.P

43. Vapour compression refrigeration is somewhat like

None of the above

Rankine’s cycle

Reversed Carnot cycle

Carnot cycle

44. Refrigeration in aeroplanes usually employs the following refrigerant

CO2

Air

Freon-22

Freon-11

45. During cooling and dehumidification, dry bulb temperature

Increases

Remains constant

None of these

Decreases

Refrigeration & Air-Conditioning Practice Set-4

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