Refrigeration & Air-Conditioning Practice Set-4

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1. 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

2. The specific humidity during dehumidification process

Remains constant

Increases

None of these

Decreases

3. The specific humidity during heating and humidification process.

Increases

Remains constant

None of these

Decreases

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

Direct

Absorption

Indirect

Compression

5. 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)]

0.622 Pv / (Pb - Pv)

μ/[1 - (1 - μ) (Ps/Pb)]

None of these

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

More than 10 kg

More than or equal to 3.65 kg

There is no such consideration

Less than 2 kg

7. Vapour compression refrigeration is somewhat like

Carnot cycle

Reversed Carnot cycle

None of the above

Rankine’s cycle

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

Increase

Decrease

May increase or decrease depending on the type of refrigerant used

Remain unaffected

9. During sensible cooling,

Specific humidity increases

Partial pressure of vapour remains constant

Relative humidity remains constant

Wet bulb temperature increases

10. The sub-cooling in a refrigeration cycle

Does not alter C.O.P.

Decreases C.O.P.

None of these

Increases C.O.P.

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11. Superheating in a refrigeration cycle

Other factors decide C.O.P

Decreases C.O.P

Increases C.O.P

C.O.P remains unaltered

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

Heat of compression

All of the above

Enthalpy increase in compressor

Work done by compressor

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

20°C DBT and 50% RH

20°C DBT and 60% RH

26°C DBT and 50% RH

26°C DBT and 60% RH

14. The advantage of dry compression is that

It permits complete evaporation in the evaporator

All of the above

It permits higher speeds to be used

It results in high volumetric and mechanical efficiency

15. The relative coefficient of performance is

None of these

Actual COP × theoretical COP

Actual COP/theoretical COP

Theoretical COP/actual COP

16. 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 - td₂)/(td₃ - td₁)

(td₂ - td₃)/(td₃ - td₁)

(td₃ - td₁)/(td₃ - td₂)

17. 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 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

18. 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

0.2

5

1.2

19. 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

20. The superheating in a refrigeration cycle

Decreases C.O.P.

Increases C.O.P.

Does not alter C.O.P.

None of these

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21. Which of the following statement is correct?

All of these

The constant enthalpy lines are also constant wet bulb temperature lines

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

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

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

Relative

None of these

Specific

Absolute

23. 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

4 kW

1 kW

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

All of these

Sulphur sticks

Soap and water

Halide torch

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

Small

Anything

High

Equal

26. Ammonia absorption refrigeration cycle requires

Very little work input

Zero work input

Nearly same work input as for vapour compression cycle

Maximum work input

27. 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

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

Freon-22

CO2

NH3

Freon-12

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

Sulphur dioxide

Ammonia

R-12

Carbon dioxide

30. The Freon group of refrigerants are

Halocarbon refrigerants

Inorganic refrigerants

Zoetrope refrigerants

Hydrocarbon refrigerants

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

Lower than

Higher than

None of these

Same as

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

Effective temperature

None of these

Dew point temperature

Mean radiant temperature

33. During cooling and dehumidification, dry bulb temperature

None of these

Increases

Decreases

Remains constant

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

Wet vapour

Superheated vapour

Saturated liquid

Dry saturated vapour

35. 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)

(h2 - hA)/ (h1 - h2)

(hA - h1)/ (h2 - h1)

(h1 - h2)/ (hA - h2)

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

Condenser and expansion valve

Compressor and evaporator

Expansion valve and evaporator

Compressor and condenser

37. Refrigeration in aeroplanes usually employs the following refrigerant

Freon-22

Freon-11

CO2

Air

38. The condensing pressure due to the presence of non-condensable gases, as compared to that actually required for condensing temperatures without non-condensable gases,

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

Will remain unaffected

Will be higher

Will be lower

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

Less

More

Same

More or less depending on ambient conditions

40. Air conditioning means

Cooling

Dehumidifying

Heating

All of these

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

Both room sensible heat and latent heat loads

Room sensible heat load only

Room latent heat load only

None of the above

42. Air refrigeration operates on

Carnot cycle

Reversed Carnot cycle

Rankine’s cycle

Brayton cycle

43. Moisture in Freon refrigeration system causes

Corrosion of whole system

High power consumption

Freezing automatic regulating valve

Ineffective refrigeration

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

Carbon dioxide

Ammonia

R-12

Sulphur dioxide

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

DX coil

None of these

Flooded

Dry

Refrigeration & Air-Conditioning Practice Set-4

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