Refrigeration & Air-Conditioning Practice Set-4

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

None of these

Higher than

Same as

Lower than

2. Refrigeration in aeroplanes usually employs the following refrigerant

Freon-22

CO2

Air

Freon-11

3. Ammonia absorption refrigeration cycle requires

Very little work input

Maximum work input

Zero work input

Nearly same work input as for vapour compression cycle

4. The specific humidity during heating and humidification process.

None of these

Remains constant

Decreases

Increases

5. 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

6. 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 - h1)/ (h2 - h1)

(h1 - h2)/ (hA - h2)

(hA - h2)/ (h1 - h2)

(h2 - hA)/ (h1 - h2)

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

Compression of the refrigerant vapour

Metering of the refrigerant liquid

Condensation of the refrigerant vapour

Evaporation of the refrigerant liquid

8. 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

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

Which is lower than the dew point temperature of the incoming stream

Of adiabatic saturation of incoming stream

9. 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

10. 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

1.2

0.2

5

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11. 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

12. The relative coefficient of performance is

Actual COP × theoretical COP

Theoretical COP/actual COP

None of these

Actual COP/theoretical COP

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

Ammonia

R-12

Carbon dioxide

Sulphur dioxide

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

Sulphur sticks

Soap and water

Halide torch

All of these

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

After passing through the expansion or throttle valve

Before entering the compressor

Before passing through the condenser

After passing through the condenser

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

There is no such consideration

More than or equal to 3.65 kg

More than 10 kg

Less than 2 kg

17. 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

None of these

Effective temperature

Mean radiant temperature

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

Direct

Absorption

Compression

Indirect

19. Vapour compression refrigeration is somewhat like

None of the above

Reversed Carnot cycle

Carnot cycle

Rankine’s cycle

20. Moisture in Freon refrigeration system causes

Corrosion of whole system

High power consumption

Ineffective refrigeration

Freezing automatic regulating valve

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

Enthalpy increase in compressor

Work done by compressor

Heat of compression

All of the above

22. Which of the following statement is correct?

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

The constant enthalpy lines are also constant wet bulb temperature lines

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

All of these

23. Superheating in a refrigeration cycle

Other factors decide C.O.P

Increases C.O.P

Decreases C.O.P

C.O.P remains unaltered

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

Superheated vapour

Saturated liquid

Dry saturated vapour

Wet vapour

25. The Freon group of refrigerants are

Halocarbon refrigerants

Inorganic refrigerants

Hydrocarbon refrigerants

Zoetrope refrigerants

26. The superheating in a refrigeration cycle

Decreases C.O.P.

None of these

Does not alter C.O.P.

Increases C.O.P.

27. The sub-cooling in a refrigeration cycle

Decreases C.O.P.

Does not alter C.O.P.

Increases C.O.P.

None of these

28. 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)

0.622 Pv / (Pb - Pv)

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

μ/[1 - (1 - μ) (Ps/Pb)]

None of these

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

Freon-12

NH3

CO2

Freon-22

30. 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

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

Will remain unaffected

Will be lower

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31. Air conditioning means

Dehumidifying

Cooling

Heating

All of these

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

High

Small

Anything

Equal

33. Air refrigeration operates on

Reversed Carnot cycle

Rankine’s cycle

Brayton cycle

Carnot cycle

34. 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 60% RH

26°C DBT and 50% RH

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

More

Same

Less

More or less depending on ambient conditions

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

None of these

Relative

Absolute

Specific

37. 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)/(td₃ - td₂)

(td₃ - td₁)/(td₂ - td₃)

(td₂ - td₃)/(td₃ - td₁)

(td₃ - td₂)/(td₃ - td₁)

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

Room latent heat load only

Room sensible heat load only

Both room sensible heat and latent heat loads

None of the above

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

Sulphur dioxide

Carbon dioxide

Ammonia

R-12

40. 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

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41. The specific humidity during dehumidification process

Remains constant

Decreases

None of these

Increases

42. During sensible cooling,

Wet bulb temperature increases

Partial pressure of vapour remains constant

Relative humidity remains constant

Specific humidity increases

43. During cooling and dehumidification, dry bulb temperature

Decreases

None of these

Remains constant

Increases

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

None of these

Dry

Flooded

DX coil

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

Compressor and evaporator

Compressor and condenser

Condenser and expansion valve

Expansion valve and evaporator

Refrigeration & Air-Conditioning Practice Set-4

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