Refrigeration & Air-Conditioning Practice Set-4

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

Freon-22

CO2

NH3

Freon-12

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

20°C DBT and 50% RH

26°C DBT and 60% RH

20°C DBT and 60% RH

26°C DBT and 50% RH

3. 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

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

Mean radiant temperature

None of these

Dew point temperature

Effective temperature

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

Higher than

None of these

Same as

Lower than

6. Air refrigeration operates on

Carnot cycle

Brayton cycle

Rankine’s cycle

Reversed Carnot cycle

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

More or less depending on ambient conditions

More

Same

Less

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

Condensation of the refrigerant vapour

Metering of the refrigerant liquid

Evaporation of the refrigerant liquid

Compression of the refrigerant vapour

9. The Freon group of refrigerants are

Zoetrope refrigerants

Halocarbon refrigerants

Inorganic refrigerants

Hydrocarbon refrigerants

10. Vapour compression refrigeration is somewhat like

Carnot cycle

Reversed Carnot cycle

None of the above

Rankine’s cycle

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

After passing through the condenser

After passing through the expansion or throttle valve

Before passing through the condenser

Before entering the compressor

12. 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

5

6

0.2

1.2

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

Sulphur dioxide

Ammonia

Carbon dioxide

R-12

14. 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 - td₁)/(td₃ - td₂)

(td₃ - td₂)/(td₃ - td₁)

(td₂ - td₃)/(td₃ - td₁)

15. During sensible cooling,

Partial pressure of vapour remains constant

Relative humidity remains constant

Specific humidity increases

Wet bulb temperature increases

16. The superheating in a refrigeration cycle

None of these

Does not alter C.O.P.

Increases C.O.P.

Decreases C.O.P.

17. Air conditioning means

Cooling

Dehumidifying

Heating

All of these

18. The specific humidity during heating and humidification process.

Remains constant

Decreases

None of these

Increases

19. 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 - h2)/ (h1 - h2)

(hA - h1)/ (h2 - h1)

(h2 - hA)/ (h1 - h2)

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

Compressor and evaporator

Expansion valve and evaporator

Compressor and condenser

Condenser and expansion valve

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

Enthalpy increase in compressor

All of the above

Heat of compression

Work done by compressor

22. 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 10 kg

Less than 2 kg

More than or equal to 3.65 kg

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

Anything

Small

Equal

High

24. Which of the following statement is correct?

All of these

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

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

The constant enthalpy lines are also constant wet bulb temperature lines

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

None of these

Relative

Absolute

Specific

26. 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

27. 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 be lower

Will remain unaffected

28. Refrigeration in aeroplanes usually employs the following refrigerant

Air

CO2

Freon-11

Freon-22

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

Ammonia

Carbon dioxide

R-12

Sulphur dioxide

30. Moisture in Freon refrigeration system causes

Freezing automatic regulating valve

High power consumption

Ineffective refrigeration

Corrosion of whole system

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

Room latent heat load only

Both room sensible heat and latent heat loads

None of the above

Room sensible heat load only

32. Superheating in a refrigeration cycle

Increases C.O.P

C.O.P remains unaltered

Decreases C.O.P

Other factors decide C.O.P

33. During cooling and dehumidification, dry bulb temperature

Remains constant

None of these

Decreases

Increases

34. The specific humidity during dehumidification process

Increases

None of these

Decreases

Remains constant

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

Mixture of ice and water under equilibrium conditions

Water at 0°C

Ice at 4°C

Solid and dry ice

36. The sub-cooling in a refrigeration cycle

Increases C.O.P.

None of these

Decreases C.O.P.

Does not alter C.O.P.

37. Ammonia absorption refrigeration cycle requires

Nearly same work input as for vapour compression cycle

Very little work input

Zero work input

Maximum work input

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

Absorption

Indirect

Direct

Compression

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

Dry saturated vapour

Wet vapour

Saturated liquid

Superheated vapour

40. 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)

None of these

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

μ/[1 - (1 - μ) (Ps/Pb)]

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41. The relative coefficient of performance is

None of these

Actual COP × theoretical COP

Actual COP/theoretical COP

Theoretical COP/actual COP

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

All of these

Halide torch

Soap and water

Sulphur sticks

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

Flooded

DX coil

Dry

None of these

44. 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

45. 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 lies between the dry bulb and wet bulb temperatures of the incoming stream

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

Refrigeration & Air-Conditioning Practice Set-4

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