Refrigeration & Air-Conditioning Practice Set-4

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1. During sensible cooling,

Wet bulb temperature increases

Partial pressure of vapour remains constant

Specific humidity increases

Relative humidity remains constant

2. Which of the following statement is correct?

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

The constant enthalpy lines are also constant wet bulb temperature lines

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

All of these

3. 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 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

4. 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

5. Air conditioning means

Heating

Dehumidifying

Cooling

All of these

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

Enthalpy increase in compressor

Heat of compression

Work done by compressor

All of the above

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

After passing through the condenser

After passing through the expansion or throttle valve

Before entering the compressor

Before passing through the condenser

8. Refrigeration in aeroplanes usually employs the following refrigerant

Freon-22

Air

Freon-11

CO2

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

DX coil

Dry

Flooded

None of these

10. 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

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

Decrease

Remain unaffected

Increase

May increase or decrease depending on the type of refrigerant used

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

Wet vapour

Dry saturated vapour

Superheated vapour

Saturated liquid

13. 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

6

1.2

5

14. The specific humidity during heating and humidification process.

Remains constant

None of these

Increases

Decreases

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

26°C DBT and 60% RH

20°C DBT and 60% RH

20°C DBT and 50% RH

26°C DBT and 50% RH

16. Ammonia absorption refrigeration cycle requires

Zero work input

Nearly same work input as for vapour compression cycle

Maximum work input

Very little work input

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

Solid and dry ice

Mixture of ice and water under equilibrium conditions

Ice at 4°C

Water at 0°C

18. 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

4 kW

1 kW

3 kW

19. Vapour compression refrigeration is somewhat like

Reversed Carnot cycle

Carnot cycle

Rankine’s cycle

None of the above

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

NH3

Freon-12

CO2

Freon-22

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21. The Freon group of refrigerants are

Hydrocarbon refrigerants

Zoetrope refrigerants

Halocarbon refrigerants

Inorganic refrigerants

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

Sulphur dioxide

Ammonia

R-12

Carbon dioxide

23. 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)]

None of these

0.622 Pv / (Pb - Pv)

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

24. During cooling and dehumidification, dry bulb temperature

None of these

Decreases

Increases

Remains constant

25. The relative coefficient of performance is

Actual COP/theoretical COP

Theoretical COP/actual COP

Actual COP × theoretical COP

None of these

26. The sub-cooling in a refrigeration cycle

Decreases C.O.P.

Does not alter C.O.P.

None of these

Increases C.O.P.

27. 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)

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

Same as

Higher than

Lower than

None of these

29. 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 higher

Will remain unaffected

Will be lower

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

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

Small

High

Equal

Anything

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

Less than 2 kg

There is no such consideration

More than 10 kg

More than or equal to 3.65 kg

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

Soap and water

Halide torch

All of these

Sulphur sticks

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

None of these

Absolute

Specific

Relative

34. Air refrigeration operates on

Brayton cycle

Reversed Carnot cycle

Carnot cycle

Rankine’s cycle

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)

(h1 - h2)/ (hA - h2)

(hA - h2)/ (h1 - h2)

(hA - h1)/ (h2 - h1)

(h2 - hA)/ (h1 - h2)

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

Evaporation of the refrigerant liquid

Compression of the refrigerant vapour

Condensation of the refrigerant vapour

Metering of the refrigerant liquid

37. The superheating in a refrigeration cycle

Decreases C.O.P.

Does not alter C.O.P.

None of these

Increases C.O.P.

38. The advantage of dry compression is that

All of the above

It results in high volumetric and mechanical efficiency

It permits complete evaporation in the evaporator

It permits higher speeds to be used

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

Indirect

Absorption

Direct

Compression

40. Superheating in a refrigeration cycle

Other factors decide C.O.P

Increases C.O.P

Decreases C.O.P

C.O.P remains unaltered

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41. Moisture in Freon refrigeration system causes

High power consumption

Ineffective refrigeration

Corrosion of whole system

Freezing automatic regulating valve

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

R-12

Carbon dioxide

Sulphur dioxide

Ammonia

43. The specific humidity during dehumidification process

Increases

Decreases

None of these

Remains constant

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

Expansion valve and evaporator

Condenser and expansion valve

Compressor and condenser

Compressor and evaporator

45. 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

Refrigeration & Air-Conditioning Practice Set-4

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