Refrigeration & Air-Conditioning Practice Set-4

Page 1 of 5

1. 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)/(td₃ - td₂)

(td₃ - td₁)/(td₂ - td₃)

(td₃ - td₂)/(td₃ - td₁)

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 - h1)/ (h2 - h1)

(h2 - hA)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

(hA - h2)/ (h1 - h2)

3. The Freon group of refrigerants are

Halocarbon refrigerants

Hydrocarbon refrigerants

Zoetrope refrigerants

Inorganic refrigerants

4. Which of the following statement is correct?

All of these

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

The constant enthalpy lines are also constant wet bulb temperature lines

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

5. 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

6. The specific humidity during dehumidification process

Remains constant

Decreases

Increases

None of these

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

Increase

Remain unaffected

May increase or decrease depending on the type of refrigerant used

Decrease

8. Air refrigeration operates on

Carnot cycle

Reversed Carnot cycle

Rankine’s cycle

Brayton cycle

9. The sub-cooling in a refrigeration cycle

Decreases C.O.P.

None of these

Does not alter C.O.P.

Increases C.O.P.

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

Enthalpy increase in compressor

All of the above

Heat of compression

Work done by compressor

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11. During cooling and dehumidification, dry bulb temperature

None of these

Decreases

Remains constant

Increases

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

Dry

None of these

Flooded

DX coil

13. During sensible cooling,

Partial pressure of vapour remains constant

Relative humidity remains constant

Specific humidity increases

Wet bulb temperature increases

14. Ammonia absorption refrigeration cycle requires

Nearly same work input as for vapour compression cycle

Maximum work input

Zero work input

Very little work input

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

20°C DBT and 60% RH

26°C DBT and 50% RH

26°C DBT and 60% RH

20°C DBT and 50% RH

16. 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

5

6

0.2

17. Refrigeration in aeroplanes usually employs the following refrigerant

CO2

Freon-22

Freon-11

Air

18. Air conditioning means

All of these

Cooling

Heating

Dehumidifying

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

Halide torch

Soap and water

All of these

Sulphur sticks

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

Expansion valve and evaporator

Condenser and expansion valve

Compressor and evaporator

Compressor and condenser

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21. Superheating in a refrigeration cycle

Other factors decide C.O.P

Increases C.O.P

C.O.P remains unaltered

Decreases C.O.P

22. The advantage of dry compression is that

It permits higher speeds to be used

All of the above

It results in high volumetric and mechanical efficiency

It permits complete evaporation in the evaporator

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

Water at 0°C

Solid and dry ice

Ice at 4°C

Mixture of ice and water under equilibrium conditions

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

Absolute

None of these

Relative

Specific

25. The superheating in a refrigeration cycle

None of these

Increases C.O.P.

Does not alter C.O.P.

Decreases C.O.P.

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

Saturated liquid

Dry saturated vapour

Superheated vapour

Wet vapour

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

Indirect

Direct

Absorption

Compression

28. Moisture in Freon refrigeration system causes

Corrosion of whole system

Freezing automatic regulating valve

Ineffective refrigeration

High power consumption

29. The relative coefficient of performance is

Theoretical COP/actual COP

Actual COP/theoretical COP

None of these

Actual COP × theoretical COP

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

CO2

Freon-12

Freon-22

NH3

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31. 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

3 kW

2 kW

1 kW

4 kW

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

Ammonia

R-12

Sulphur dioxide

Carbon dioxide

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

Condensation of the refrigerant vapour

Metering of the refrigerant liquid

Evaporation of the refrigerant liquid

Compression of the refrigerant vapour

34. The specific humidity during heating and humidification process.

Decreases

None of these

Increases

Remains constant

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

Same

Less

More

More or less depending on ambient conditions

36. 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 or equal to 3.65 kg

More than 10 kg

Less than 2 kg

37. 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

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

Will be higher

Will remain unaffected

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

Lower than

None of these

Same as

Higher than

39. 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)

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

μ/[1 - (1 - μ) (Ps/Pb)]

None of these

0.622 Pv / (Pb - Pv)

40. 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

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

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

Ammonia

R-12

Carbon dioxide

Sulphur dioxide

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

Equal

Anything

Small

High

43. 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

Room sensible heat load only

None of the above

44. 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

Effective temperature

None of these

Mean radiant temperature

45. Vapour compression refrigeration is somewhat like

None of the above

Rankine’s cycle

Carnot cycle

Reversed Carnot cycle

Refrigeration & Air-Conditioning Practice Set-4

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