Refrigeration & Air-Conditioning Practice Set-4

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1. The sub-cooling in a refrigeration cycle

Increases C.O.P.

Does not alter C.O.P.

Decreases C.O.P.

None of these

2. 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

0.2

6

1.2

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

Remain unaffected

Decrease

May increase or decrease depending on the type of refrigerant used

Increase

4. The Freon group of refrigerants are

Halocarbon refrigerants

Zoetrope refrigerants

Inorganic refrigerants

Hydrocarbon refrigerants

5. The relative coefficient of performance is

Theoretical COP/actual COP

Actual COP/theoretical COP

Actual COP × theoretical COP

None of these

6. During sensible cooling,

Partial pressure of vapour remains constant

Wet bulb temperature increases

Relative humidity remains constant

Specific humidity increases

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

More

Less

More or less depending on ambient conditions

Same

9. The superheating in a refrigeration cycle

Decreases C.O.P.

None of these

Increases C.O.P.

Does not alter C.O.P.

10. 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

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11. The advantage of dry compression is that

It permits higher speeds to be used

All of the above

It results in high volumetric and mechanical efficiency

It permits complete evaporation in the evaporator

12. 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

1 kW

3 kW

2 kW

4 kW

13. Which of the following statement is correct?

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

All of these

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

All of the above

Work done by compressor

Heat of compression

Enthalpy increase in compressor

15. 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)]

None of these

0.622 Pv / (Pb - Pv)

μ/[1 - (1 - μ) (Ps/Pb)]

16. 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

Effective temperature

Dew point temperature

None of these

17. 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 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

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

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

NH3

Freon-12

Freon-22

CO2

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)

(hA - h1)/ (h2 - h1)

(hA - h2)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

(h2 - hA)/ (h1 - h2)

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

All of these

Sulphur sticks

Soap and water

Halide torch

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21. During cooling and dehumidification, dry bulb temperature

None of these

Decreases

Remains constant

Increases

22. Refrigeration in aeroplanes usually employs the following refrigerant

CO2

Air

Freon-22

Freon-11

23. Vapour compression refrigeration is somewhat like

Reversed Carnot cycle

None of the above

Carnot cycle

Rankine’s cycle

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

Metering of the refrigerant liquid

Condensation of the refrigerant vapour

Compression of the refrigerant vapour

Evaporation of the refrigerant liquid

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

High

Anything

Small

Equal

26. The specific humidity during heating and humidification process.

None of these

Increases

Remains constant

Decreases

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 remain unaffected

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

Will be higher

Will be lower

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

R-12

Sulphur dioxide

Ammonia

Carbon dioxide

29. 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

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

Compressor and condenser

Compressor and evaporator

Condenser and expansion valve

Expansion valve and evaporator

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

Lower than

Higher than

Same as

None of these

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

Mixture of ice and water under equilibrium conditions

Solid and dry ice

Water at 0°C

Ice at 4°C

33. 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)

(td₃ - td₁)/(td₂ - td₃)

(td₃ - td₁)/(td₃ - td₂)

(td₂ - td₃)/(td₃ - td₁)

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

Ammonia

Sulphur dioxide

R-12

Carbon dioxide

35. Air conditioning means

All of these

Dehumidifying

Heating

Cooling

36. Ammonia absorption refrigeration cycle requires

Nearly same work input as for vapour compression cycle

Zero work input

Very little work input

Maximum work input

37. 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

More than or equal to 3.65 kg

Less than 2 kg

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

Before entering the compressor

After passing through the condenser

After passing through the expansion or throttle valve

Before passing through the condenser

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

None of these

Specific

Relative

Absolute

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

Indirect

Compression

Absorption

Direct

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41. Air refrigeration operates on

Carnot cycle

Reversed Carnot cycle

Rankine’s cycle

Brayton cycle

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

Dry saturated vapour

Saturated liquid

Wet vapour

Superheated vapour

43. Moisture in Freon refrigeration system causes

Freezing automatic regulating valve

Corrosion of whole system

Ineffective refrigeration

High power consumption

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

DX coil

Dry

Flooded

None of these

45. The specific humidity during dehumidification process

Remains constant

Decreases

None of these

Increases

Refrigeration & Air-Conditioning Practice Set-4

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