Refrigeration & Air-Conditioning Practice Set-4

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1. Vapour compression refrigeration is somewhat like

Carnot cycle

None of the above

Rankine’s cycle

Reversed Carnot cycle

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

Same as

Higher than

None of these

Lower than

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

Ammonia

Carbon dioxide

Sulphur dioxide

R-12

4. The Freon group of refrigerants are

Hydrocarbon refrigerants

Inorganic refrigerants

Zoetrope refrigerants

Halocarbon refrigerants

5. The superheating in a refrigeration cycle

Does not alter C.O.P.

None of these

Decreases C.O.P.

Increases C.O.P.

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

Effective temperature

Dew point temperature

None of these

Mean radiant temperature

7. The specific humidity during dehumidification process

None of these

Increases

Decreases

Remains constant

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

Sulphur sticks

Soap and water

Halide torch

All of these

9. Moisture in Freon refrigeration system causes

Corrosion of whole system

Freezing automatic regulating valve

High power consumption

Ineffective refrigeration

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

Condenser and expansion valve

Expansion valve and evaporator

Compressor and evaporator

Compressor and condenser

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11. Superheating in a refrigeration cycle

Decreases C.O.P

Increases C.O.P

C.O.P remains unaltered

Other factors decide C.O.P

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

Direct

Indirect

Absorption

Compression

13. The specific humidity during heating and humidification process.

None of these

Increases

Decreases

Remains constant

14. 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

15. 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)

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

μ/[1 - (1 - μ) (Ps/Pb)]

None of these

16. 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 - h1)/ (h2 - h1)

(h1 - h2)/ (hA - h2)

(hA - h2)/ (h1 - h2)

(h2 - hA)/ (h1 - h2)

17. Refrigeration in aeroplanes usually employs the following refrigerant

Air

CO2

Freon-22

Freon-11

18. 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

Remain unaffected

Decrease

19. The sub-cooling in a refrigeration cycle

Does not alter C.O.P.

Decreases C.O.P.

None of these

Increases C.O.P.

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

Sulphur dioxide

Ammonia

R-12

Carbon dioxide

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

Metering of the refrigerant liquid

Compression of the refrigerant vapour

Condensation of the refrigerant vapour

Evaporation of the refrigerant liquid

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

Small

Anything

Equal

High

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

Mixture of ice and water under equilibrium conditions

Water at 0°C

Solid and dry ice

Ice at 4°C

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

Both room sensible heat and latent heat loads

None of the above

Room latent heat load only

Room sensible heat load only

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

More than 10 kg

There is no such consideration

More than or equal to 3.65 kg

Less than 2 kg

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

Freon-12

Freon-22

CO2

NH3

27. During cooling and dehumidification, dry bulb temperature

Increases

Decreases

Remains constant

None of these

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

DX coil

None of these

Flooded

Dry

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

Superheated vapour

Wet vapour

Dry saturated vapour

Saturated liquid

30. 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

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

Will be higher

Will be lower

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31. 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

More

32. Which of the following statement is correct?

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

All of these

The constant enthalpy lines are also constant wet bulb temperature lines

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

33. 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

6

5

0.2

1.2

34. During sensible cooling,

Relative humidity remains constant

Wet bulb temperature increases

Partial pressure of vapour remains constant

Specific humidity increases

35. The advantage of dry compression is that

All of the above

It permits higher speeds to be used

It permits complete evaporation in the evaporator

It results in high volumetric and mechanical efficiency

36. The relative coefficient of performance is

Theoretical COP/actual COP

Actual COP/theoretical COP

None of these

Actual COP × theoretical COP

37. 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

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

20°C DBT and 50% RH

26°C DBT and 60% RH

20°C DBT and 60% RH

26°C DBT and 50% RH

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

Specific

None of these

Absolute

Relative

40. 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

4 kW

1 kW

2 kW

3 kW

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41. Air refrigeration operates on

Carnot cycle

Brayton cycle

Reversed Carnot cycle

Rankine’s cycle

42. Air conditioning means

Cooling

All of these

Dehumidifying

Heating

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)

(td₃ - td₁)/(td₃ - td₂)

(td₂ - td₃)/(td₃ - td₁)

(td₃ - td₂)/(td₃ - td₁)

44. 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

45. Ammonia absorption refrigeration cycle requires

Zero work input

Nearly same work input as for vapour compression cycle

Maximum work input

Very little work input

Refrigeration & Air-Conditioning Practice Set-4

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