Refrigeration & Air-Conditioning Practice Set-4

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1. 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

Of adiabatic saturation of 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

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

CO2

NH3

Freon-12

Freon-22

3. The specific humidity during dehumidification process

Remains constant

Decreases

None of these

Increases

4. 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)]

None of these

0.622 Pv / (Pb - Pv)

μ/[1 - (1 - μ) (Ps/Pb)]

5. 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

3 kW

4 kW

1 kW

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

Carbon dioxide

Ammonia

R-12

Sulphur dioxide

7. Superheating in a refrigeration cycle

C.O.P remains unaltered

Other factors decide C.O.P

Increases C.O.P

Decreases C.O.P

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

Water at 0°C

Mixture of ice and water under equilibrium conditions

Ice at 4°C

Solid and dry ice

9. The advantage of dry compression is that

All of the above

It permits higher speeds to be used

It results in high volumetric and mechanical efficiency

It permits complete evaporation in the evaporator

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

None of these

Flooded

DX coil

Dry

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

Compressor and condenser

Compressor and evaporator

Expansion valve and evaporator

Condenser and expansion valve

12. The superheating in a refrigeration cycle

Does not alter C.O.P.

None of these

Decreases C.O.P.

Increases C.O.P.

13. Ammonia absorption refrigeration cycle requires

Very little work input

Zero work input

Maximum work input

Nearly same work input as for vapour compression cycle

14. The specific humidity during heating and humidification process.

Increases

Decreases

Remains constant

None of these

15. 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

5

1.2

16. Air conditioning means

All of these

Dehumidifying

Cooling

Heating

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

None of these

Lower than

Higher than

Same as

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

There is no such consideration

Less than 2 kg

More than 10 kg

More than or equal to 3.65 kg

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

Enthalpy increase in compressor

Heat of compression

All of the above

Work done by compressor

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

Dry saturated vapour

Superheated vapour

Saturated liquid

Wet vapour

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21. Vapour compression refrigeration is somewhat like

Carnot cycle

Reversed Carnot cycle

None of the above

Rankine’s cycle

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

After passing through the expansion or throttle valve

After passing through the condenser

Before entering the compressor

Before passing through the condenser

23. The sub-cooling in a refrigeration cycle

Decreases C.O.P.

Increases C.O.P.

Does not alter C.O.P.

None of these

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

High

Anything

Equal

Small

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

May increase or decrease depending on the type of refrigerant used

Increase

Remain unaffected

Decrease

26. Moisture in Freon refrigeration system causes

Corrosion of whole system

Ineffective refrigeration

High power consumption

Freezing automatic regulating valve

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

None of these

Effective temperature

Mean radiant temperature

Dew point temperature

28. 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

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

All of these

Halide torch

Sulphur sticks

Soap and water

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

26°C DBT and 50% RH

26°C DBT and 60% RH

20°C DBT and 50% RH

20°C DBT and 60% RH

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

Direct

Indirect

Compression

Absorption

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

Same

More or less depending on ambient conditions

More

Less

33. Refrigeration in aeroplanes usually employs the following refrigerant

Air

Freon-22

Freon-11

CO2

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

None of the above

Room sensible heat load only

Both room sensible heat and latent heat loads

Room latent heat load only

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

Relative

Specific

None of these

Absolute

36. During cooling and dehumidification, dry bulb temperature

None of these

Remains constant

Decreases

Increases

37. 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 - h1)/ (h2 - h1)

(h2 - hA)/ (h1 - h2)

(hA - h2)/ (h1 - h2)

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

Compression of the refrigerant vapour

Evaporation of the refrigerant liquid

Condensation of the refrigerant vapour

Metering of the refrigerant liquid

39. The Freon group of refrigerants are

Hydrocarbon refrigerants

Inorganic refrigerants

Halocarbon refrigerants

Zoetrope refrigerants

40. 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 - td₂)/(td₃ - td₁)

(td₃ - td₁)/(td₃ - td₂)

(td₃ - td₁)/(td₂ - td₃)

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41. 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 remain unaffected

Will be higher

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

Will be lower

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

R-12

Ammonia

Sulphur dioxide

Carbon dioxide

43. The relative coefficient of performance is

Actual COP × theoretical COP

Actual COP/theoretical COP

None of these

Theoretical COP/actual COP

44. Air refrigeration operates on

Reversed Carnot cycle

Brayton cycle

Carnot cycle

Rankine’s cycle

45. During sensible cooling,

Specific humidity increases

Relative humidity remains constant

Partial pressure of vapour remains constant

Wet bulb temperature increases

Refrigeration & Air-Conditioning Practice Set-4

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