Refrigeration & Air-Conditioning Practice Set-4

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1. 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)

(hA - h2)/ (h1 - h2)

(h2 - hA)/ (h1 - h2)

2. Refrigeration in aeroplanes usually employs the following refrigerant

Air

Freon-11

Freon-22

CO2

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

Sulphur dioxide

Carbon dioxide

Ammonia

R-12

4. During sensible cooling,

Wet bulb temperature increases

Partial pressure of vapour remains constant

Specific humidity increases

Relative humidity remains constant

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

Higher than

Same as

Lower than

None of these

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

Before entering the compressor

Before passing through the condenser

After passing through the condenser

After passing through the expansion or throttle valve

7. Superheating in a refrigeration cycle

Decreases C.O.P

C.O.P remains unaltered

Increases C.O.P

Other factors decide C.O.P

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

Saturated liquid

Dry saturated vapour

Wet vapour

Superheated vapour

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

Ice at 4°C

Mixture of ice and water under equilibrium conditions

Solid and dry ice

Water at 0°C

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

NH3

CO2

Freon-12

Freon-22

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11. 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)/(td₂ - td₃)

(td₃ - td₁)/(td₃ - td₂)

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

Flooded

None of these

Dry

DX coil

13. The advantage of dry compression is that

All of the above

It permits higher speeds to be used

It permits complete evaporation in the evaporator

It results in high volumetric and mechanical efficiency

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

Effective temperature

Dew point temperature

None of these

Mean radiant temperature

15. 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

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

Specific

Absolute

Relative

None of these

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

Compression

Direct

Indirect

Absorption

18. The Freon group of refrigerants are

Hydrocarbon refrigerants

Zoetrope refrigerants

Halocarbon refrigerants

Inorganic refrigerants

19. The sub-cooling in a refrigeration cycle

Increases C.O.P.

Decreases C.O.P.

Does not alter C.O.P.

None of these

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

Less

More

More or less depending on ambient conditions

Same

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21. Air refrigeration operates on

Brayton cycle

Reversed Carnot cycle

Carnot cycle

Rankine’s cycle

22. 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

23. The specific humidity during dehumidification process

Increases

None of these

Decreases

Remains constant

24. Moisture in Freon refrigeration system causes

Corrosion of whole system

High power consumption

Freezing automatic regulating valve

Ineffective refrigeration

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

Equal

Anything

Small

High

26. Ammonia absorption refrigeration cycle requires

Maximum work input

Nearly same work input as for vapour compression cycle

Zero work input

Very little work input

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

Ammonia

R-12

Carbon dioxide

Sulphur dioxide

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

Compressor and evaporator

Compressor and condenser

Condenser and expansion valve

Expansion valve and evaporator

29. The superheating in a refrigeration cycle

Increases C.O.P.

Does not alter C.O.P.

None of these

Decreases C.O.P.

30. The relative coefficient of performance is

Actual COP/theoretical COP

Theoretical COP/actual COP

None of these

Actual COP × theoretical COP

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31. 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

32. The specific humidity during heating and humidification process.

None of these

Increases

Decreases

Remains constant

33. Air conditioning means

Cooling

Dehumidifying

All of these

Heating

34. 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

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

Sulphur sticks

All of these

Halide torch

Soap and water

36. 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

0.2

5

6

37. 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

4 kW

2 kW

3 kW

1 kW

38. During cooling and dehumidification, dry bulb temperature

None of these

Remains constant

Increases

Decreases

39. 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)]

0.622 Pv / (Pb - Pv)

None of these

μ/[1 - (1 - μ) (Ps/Pb)]

40. Vapour compression refrigeration is somewhat like

Rankine’s cycle

Carnot cycle

Reversed Carnot cycle

None of the above

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

Decrease

Increase

May increase or decrease depending on the type of refrigerant used

Remain unaffected

42. 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

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

Metering of the refrigerant liquid

Evaporation of the refrigerant liquid

Compression of the refrigerant vapour

Condensation of the refrigerant vapour

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

Room sensible heat load only

Room latent heat load only

None of the above

Both room sensible heat and latent heat loads

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

Work done by compressor

All of the above

Heat of compression

Enthalpy increase in compressor

Refrigeration & Air-Conditioning Practice Set-4

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