Refrigeration & Air-Conditioning Practice Set-4

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1. 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

Decrease

Remain unaffected

Increase

2. Air refrigeration operates on

Carnot cycle

Brayton cycle

Reversed Carnot cycle

Rankine’s cycle

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

All of the above

Enthalpy increase in compressor

Heat of compression

Work done by compressor

4. Superheating in a refrigeration cycle

C.O.P remains unaltered

Other factors decide C.O.P

Increases C.O.P

Decreases C.O.P

5. Refrigeration in aeroplanes usually employs the following refrigerant

CO2

Air

Freon-22

Freon-11

6. 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

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

20°C DBT and 50% RH

26°C DBT and 60% RH

26°C DBT and 50% RH

20°C DBT and 60% RH

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

Saturated liquid

Superheated vapour

Dry saturated vapour

Wet vapour

9. 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

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

Higher than

Same as

None of these

Lower than

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

Effective temperature

Mean radiant temperature

None of these

Dew point temperature

12. Which of the following statement is correct?

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

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

All of these

The constant enthalpy lines are also constant wet bulb temperature lines

13. The superheating in a refrigeration cycle

None of these

Does not alter C.O.P.

Increases C.O.P.

Decreases C.O.P.

14. 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

15. 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)

16. Moisture in Freon refrigeration system causes

Freezing automatic regulating valve

Ineffective refrigeration

High power consumption

Corrosion of whole system

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

More than 10 kg

Less than 2 kg

There is no such consideration

More than or equal to 3.65 kg

18. The Freon group of refrigerants are

Hydrocarbon refrigerants

Inorganic refrigerants

Halocarbon refrigerants

Zoetrope refrigerants

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

Sulphur sticks

Soap and water

Halide torch

All of these

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

Water at 0°C

Ice at 4°C

Mixture of ice and water under equilibrium conditions

Solid and dry ice

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

Indirect

Direct

Compression

Absorption

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

Expansion valve and evaporator

Compressor and condenser

Compressor and evaporator

Condenser and expansion valve

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

CO2

Freon-22

Freon-12

NH3

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

Sulphur dioxide

Carbon dioxide

R-12

Ammonia

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

Both room sensible heat and latent heat loads

None of the above

Room latent heat load only

Room sensible heat load only

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

Before passing through the condenser

After passing through the condenser

After passing through the expansion or throttle valve

Before entering the compressor

27. The specific humidity during dehumidification process

Decreases

Increases

Remains constant

None of these

28. 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)

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

Relative

None of these

Absolute

Specific

30. Air conditioning means

Heating

Cooling

Dehumidifying

All of these

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

DX coil

Dry

None of these

Flooded

32. 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

1.2

5

6

33. The advantage of dry compression is that

It permits higher speeds to be used

All of the above

It permits complete evaporation in the evaporator

It results in high volumetric and mechanical efficiency

34. Vapour compression refrigeration is somewhat like

Carnot cycle

None of the above

Rankine’s cycle

Reversed Carnot cycle

35. The specific humidity during heating and humidification process.

Remains constant

Increases

Decreases

None of these

36. 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 lower

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

Will be higher

37. 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

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

Of adiabatic saturation of incoming stream

38. The sub-cooling in a refrigeration cycle

Increases C.O.P.

Decreases C.O.P.

None of these

Does not alter C.O.P.

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

Carbon dioxide

Sulphur dioxide

R-12

Ammonia

40. The relative coefficient of performance is

Theoretical COP/actual COP

Actual COP/theoretical COP

None of these

Actual COP × theoretical COP

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41. Ammonia absorption refrigeration cycle requires

Maximum work input

Nearly same work input as for vapour compression cycle

Very little work input

Zero work input

42. During sensible cooling,

Specific humidity increases

Wet bulb temperature increases

Relative humidity remains constant

Partial pressure of vapour remains constant

43. During cooling and dehumidification, dry bulb temperature

Increases

Remains constant

None of these

Decreases

44. 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

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

Anything

Small

Equal

High

Refrigeration & Air-Conditioning Practice Set-4

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