Refrigeration & Air-Conditioning Practice Set-4

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1. 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)

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

Solid and dry ice

Water at 0°C

Mixture of ice and water under equilibrium conditions

Ice at 4°C

3. 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

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

Ammonia

Sulphur dioxide

Carbon dioxide

R-12

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

Absorption

Indirect

Direct

Compression

6. 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

4 kW

2 kW

1 kW

7. Air conditioning means

Cooling

Dehumidifying

Heating

All of these

8. During sensible cooling,

Partial pressure of vapour remains constant

Relative humidity remains constant

Specific humidity increases

Wet bulb temperature increases

9. 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

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

Ammonia

Sulphur dioxide

R-12

Carbon dioxide

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

Saturated liquid

Superheated vapour

Dry saturated vapour

Wet vapour

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. During cooling and dehumidification, dry bulb temperature

Decreases

Increases

Remains constant

None of these

14. The specific humidity during dehumidification process

Increases

Remains constant

None of these

Decreases

15. 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 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

Which lies between the wet bulb and dew point temperatures of the incoming stream

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)

(td₃ - td₁)/(td₃ - td₂)

(td₂ - td₃)/(td₃ - td₁)

17. The specific humidity during heating and humidification process.

None of these

Remains constant

Increases

Decreases

18. Refrigeration in aeroplanes usually employs the following refrigerant

Freon-22

Freon-11

Air

CO2

19. 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

20. 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

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21. 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

Mean radiant temperature

None of these

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

Same as

None of these

Lower than

Higher than

23. 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

Will be higher

Will remain unaffected

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

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

Before entering the compressor

After passing through the expansion or throttle valve

After passing through the condenser

Before passing through the condenser

25. Moisture in Freon refrigeration system causes

Corrosion of whole system

Freezing automatic regulating valve

Ineffective refrigeration

High power consumption

26. 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

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

None of these

Relative

Specific

Absolute

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

Less

More or less depending on ambient conditions

Same

More

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

Decrease

Increase

Remain unaffected

May increase or decrease depending on the type of refrigerant used

30. 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)

(h1 - h2)/ (hA - h2)

(h2 - hA)/ (h1 - h2)

(hA - h1)/ (h2 - h1)

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

DX coil

Flooded

None of these

Dry

32. The Freon group of refrigerants are

Hydrocarbon refrigerants

Zoetrope refrigerants

Inorganic refrigerants

Halocarbon refrigerants

33. The relative coefficient of performance is

Theoretical COP/actual COP

Actual COP × theoretical COP

None of these

Actual COP/theoretical COP

34. Which of the following statement is correct?

All of these

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

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

Anything

Equal

High

Small

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

Halide torch

Sulphur sticks

Soap and water

All of these

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

None of the above

Room latent heat load only

Room sensible heat load only

Both room sensible heat and latent heat loads

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

Compressor and evaporator

Compressor and condenser

Condenser and expansion valve

Expansion valve and evaporator

39. Ammonia absorption refrigeration cycle requires

Very little work input

Zero work input

Nearly same work input as for vapour compression cycle

Maximum work input

40. The superheating in a refrigeration cycle

Increases C.O.P.

Decreases C.O.P.

Does not alter C.O.P.

None of these

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41. Air refrigeration operates on

Carnot cycle

Rankine’s cycle

Reversed Carnot cycle

Brayton cycle

42. Vapour compression refrigeration is somewhat like

Reversed Carnot cycle

None of the above

Carnot cycle

Rankine’s cycle

43. The sub-cooling in a refrigeration cycle

Increases C.O.P.

Decreases C.O.P.

Does not alter C.O.P.

None of these

44. Superheating in a refrigeration cycle

C.O.P remains unaltered

Other factors decide C.O.P

Increases C.O.P

Decreases C.O.P

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

CO2

Freon-22

Freon-12

NH3

Refrigeration & Air-Conditioning Practice Set-4

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