Refrigeration & Air-Conditioning Practice Set-4

Page 1 of 5

1. During cooling and dehumidification, dry bulb temperature

None of these

Remains constant

Increases

Decreases

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

Evaporation of the refrigerant liquid

Metering of the refrigerant liquid

Compression of the refrigerant vapour

Condensation of the refrigerant vapour

3. The specific humidity during dehumidification process

Decreases

Remains constant

Increases

None of these

4. The relative coefficient of performance is

Theoretical COP/actual COP

None of these

Actual COP × theoretical COP

Actual COP/theoretical COP

5. 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

6

0.2

5

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

Specific

Absolute

None of these

Relative

7. 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 condenser

After passing through the expansion or throttle valve

8. Moisture in Freon refrigeration system causes

Ineffective refrigeration

High power consumption

Corrosion of whole system

Freezing automatic regulating valve

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

None of these

DX coil

Dry

Flooded

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

NH3

Freon-22

Freon-12

CO2

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11. 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)

μ/[1 - (1 - μ) (Ps/Pb)]

None of these

12. 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

13. 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

2 kW

1 kW

4 kW

14. The specific humidity during heating and humidification process.

Decreases

Increases

None of these

Remains constant

15. Superheating in a refrigeration cycle

Increases C.O.P

C.O.P remains unaltered

Decreases C.O.P

Other factors decide C.O.P

16. Air refrigeration operates on

Rankine’s cycle

Reversed Carnot cycle

Carnot cycle

Brayton cycle

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

Higher than

None of these

Same as

Lower than

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

Ice at 4°C

Solid and dry ice

Mixture of ice and water under equilibrium conditions

Water at 0°C

19. The superheating in a refrigeration cycle

None of these

Does not alter C.O.P.

Decreases C.O.P.

Increases C.O.P.

20. 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 wet bulb and dew point temperatures of the incoming stream

Of adiabatic saturation of incoming stream

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

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

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21. Air conditioning means

Heating

Cooling

All of these

Dehumidifying

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

High

Anything

Equal

Small

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

More or less depending on ambient conditions

Less

Same

More

24. Ammonia absorption refrigeration cycle requires

Zero work input

Nearly same work input as for vapour compression cycle

Very little work input

Maximum work input

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

Sulphur sticks

Soap and water

All of these

Halide torch

26. 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

Remain unaffected

Increase

Decrease

27. During sensible cooling,

Specific humidity increases

Partial pressure of vapour remains constant

Relative humidity remains constant

Wet bulb temperature increases

28. Which of the following statement is correct?

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

All of these

The constant enthalpy lines are also constant wet bulb temperature lines

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

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

Sulphur dioxide

Ammonia

R-12

Carbon dioxide

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 lower

Will remain unaffected

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

Will be higher

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31. Refrigeration in aeroplanes usually employs the following refrigerant

Freon-22

CO2

Air

Freon-11

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

26°C DBT and 60% RH

20°C DBT and 60% RH

26°C DBT and 50% RH

20°C DBT and 50% RH

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

Room sensible heat load only

Room latent heat load only

Both room sensible heat and latent heat loads

None of the above

34. The sub-cooling in a refrigeration cycle

Increases C.O.P.

Does not alter C.O.P.

Decreases C.O.P.

None of these

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

Sulphur dioxide

Ammonia

Carbon dioxide

R-12

36. 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)

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

Wet vapour

Superheated vapour

Dry saturated vapour

Saturated liquid

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

More than 10 kg

More than or equal to 3.65 kg

Less than 2 kg

There is no such consideration

39. 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)

(hA - h2)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

(hA - h1)/ (h2 - h1)

40. The Freon group of refrigerants are

Hydrocarbon refrigerants

Zoetrope refrigerants

Halocarbon refrigerants

Inorganic refrigerants

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

Direct

Indirect

Compression

Absorption

42. Vapour compression refrigeration is somewhat like

Carnot cycle

Reversed Carnot cycle

Rankine’s cycle

None of the above

43. The advantage of dry compression is that

It permits complete evaporation in the evaporator

It permits higher speeds to be used

It results in high volumetric and mechanical efficiency

All of the above

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

Expansion valve and evaporator

Compressor and condenser

Compressor and evaporator

Condenser and expansion valve

45. 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

Dew point temperature

Effective temperature

Mean radiant temperature

Refrigeration & Air-Conditioning Practice Set-4

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