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. Air conditioning means

All of these

Cooling

Dehumidifying

Heating

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

Less

More or less depending on ambient conditions

More

Same

4. The superheating in a refrigeration cycle

Increases C.O.P.

None of these

Does not alter C.O.P.

Decreases C.O.P.

5. The advantage of dry compression is that

All of the above

It results in high volumetric and mechanical efficiency

It permits higher speeds to be used

It permits complete evaporation in the evaporator

6. 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 - td₂)/(td₃ - td₁)

(td₂ - td₃)/(td₃ - td₁)

(td₃ - td₁)/(td₃ - td₂)

(td₃ - td₁)/(td₂ - td₃)

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

Saturated liquid

Dry saturated vapour

Wet vapour

Superheated vapour

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

Increase

Decrease

Remain unaffected

May increase or decrease depending on the type of refrigerant used

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

Freon-12

NH3

Freon-22

CO2

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

None of these

DX coil

Dry

Flooded

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

Water at 0°C

Solid and dry ice

Mixture of ice and water under equilibrium conditions

Ice at 4°C

12. The sub-cooling in a refrigeration cycle

Increases C.O.P.

Decreases C.O.P.

Does not alter C.O.P.

None of these

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

Soap and water

Halide torch

Sulphur sticks

All of these

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

Compressor and evaporator

Expansion valve and evaporator

Condenser and expansion valve

Compressor and condenser

15. 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

1 kW

4 kW

3 kW

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

Sulphur dioxide

Ammonia

Carbon dioxide

R-12

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

Small

Equal

Anything

High

18. 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)

(h2 - hA)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

(hA - h1)/ (h2 - h1)

(hA - h2)/ (h1 - h2)

19. In order to cool and dehumidify a stream of moist air, it must be passed over the coil at a temperature

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

Of adiabatic saturation of incoming stream

Which lies between the dry bulb and wet bulb temperatures of the incoming stream

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

Relative

Specific

None of these

Absolute

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

Carbon dioxide

Ammonia

R-12

Sulphur dioxide

22. Which of the following statement is correct?

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

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

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

Higher than

Lower than

Same as

None of these

24. Superheating in a refrigeration cycle

Decreases C.O.P

C.O.P remains unaltered

Increases C.O.P

Other factors decide C.O.P

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

Room latent heat load only

None of the above

Room sensible heat load only

Both room sensible heat and latent heat loads

26. Air refrigeration operates on

Carnot cycle

Reversed Carnot cycle

Rankine’s cycle

Brayton cycle

27. Ammonia absorption refrigeration cycle requires

Very little work input

Nearly same work input as for vapour compression cycle

Maximum work input

Zero work input

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

Indirect

Direct

Compression

Absorption

29. 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

Mean radiant temperature

Dew point temperature

30. Refrigeration in aeroplanes usually employs the following refrigerant

Freon-11

CO2

Air

Freon-22

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31. The specific humidity during dehumidification process

Remains constant

Decreases

None of these

Increases

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

All of the above

Heat of compression

Enthalpy increase in compressor

Work done by compressor

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

Evaporation of the refrigerant liquid

Metering of the refrigerant liquid

Condensation of the refrigerant vapour

Compression of the refrigerant vapour

34. The specific humidity during heating and humidification process.

Remains constant

None of these

Increases

Decreases

35. 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 lower

Will be higher

36. Vapour compression refrigeration is somewhat like

None of the above

Rankine’s cycle

Reversed Carnot cycle

Carnot cycle

37. During cooling and dehumidification, dry bulb temperature

Remains constant

Increases

Decreases

None of these

38. Moisture in Freon refrigeration system causes

High power consumption

Corrosion of whole system

Freezing automatic regulating valve

Ineffective refrigeration

39. 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

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

20°C DBT and 60% RH

20°C DBT and 50% RH

26°C DBT and 50% RH

26°C DBT and 60% RH

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41. 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

0.2

6

42. 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)

43. The Freon group of refrigerants are

Hydrocarbon refrigerants

Halocarbon refrigerants

Inorganic refrigerants

Zoetrope refrigerants

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

More than or equal to 3.65 kg

There is no such consideration

Less than 2 kg

More than 10 kg

45. The relative coefficient of performance is

Actual COP × theoretical COP

None of these

Actual COP/theoretical COP

Theoretical COP/actual COP

Refrigeration & Air-Conditioning Practice Set-4

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