Refrigeration & Air-Conditioning Practice Set-4

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1. The Freon group of refrigerants are

Inorganic refrigerants

Halocarbon refrigerants

Hydrocarbon refrigerants

Zoetrope refrigerants

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

0.2

6

5

1.2

3. Vapour compression refrigeration is somewhat like

Reversed Carnot cycle

Rankine’s cycle

Carnot cycle

None of the above

4. The specific humidity during dehumidification process

Remains constant

Increases

None of these

Decreases

5. During sensible cooling,

Specific humidity increases

Relative humidity remains constant

Partial pressure of vapour remains constant

Wet bulb temperature increases

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

Freon-22

NH3

Freon-12

CO2

7. 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

4 kW

3 kW

2 kW

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

Soap and water

Halide torch

All of these

Sulphur sticks

9. Moisture in Freon refrigeration system causes

High power consumption

Freezing automatic regulating valve

Corrosion of whole system

Ineffective refrigeration

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

20°C DBT and 50% RH

20°C DBT and 60% RH

26°C DBT and 50% RH

26°C DBT and 60% RH

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11. The specific humidity during heating and humidification process.

None of these

Increases

Remains constant

Decreases

12. 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 be higher

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

Will remain unaffected

13. 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

Increase

Decrease

Remain unaffected

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

Metering of the refrigerant liquid

Compression of the refrigerant vapour

Condensation of the refrigerant vapour

Evaporation of the refrigerant liquid

15. 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 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

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

Equal

High

Small

Anything

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

Lower than

Higher than

None of these

Same as

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

Compression

Direct

Absorption

Indirect

19. 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 - td₁)/(td₂ - td₃)

(td₃ - td₁)/(td₃ - td₂)

(td₃ - td₂)/(td₃ - td₁)

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

Work done by compressor

Enthalpy increase in compressor

Heat of compression

All of the above

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21. Which of the following statement is correct?

All of these

The constant enthalpy lines are also constant wet bulb temperature lines

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

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

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

Less than 2 kg

More than or equal to 3.65 kg

There is no such consideration

More than 10 kg

23. 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 - h2)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

(h2 - hA)/ (h1 - h2)

(hA - h1)/ (h2 - h1)

24. Refrigeration in aeroplanes usually employs the following refrigerant

Freon-11

Freon-22

Air

CO2

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

None of these

Dry

DX coil

Flooded

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

Saturated liquid

Superheated vapour

Wet vapour

Dry saturated vapour

27. Superheating in a refrigeration cycle

C.O.P remains unaltered

Decreases C.O.P

Other factors decide C.O.P

Increases C.O.P

28. The relative coefficient of performance is

None of these

Theoretical COP/actual COP

Actual COP × theoretical COP

Actual COP/theoretical COP

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

Ammonia

Carbon dioxide

Sulphur dioxide

R-12

30. Air conditioning means

All of these

Dehumidifying

Heating

Cooling

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31. 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

32. During cooling and dehumidification, dry bulb temperature

Remains constant

Increases

Decreases

None of these

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

Room sensible heat load only

Both room sensible heat and latent heat loads

None of the above

Room latent heat load only

34. Air refrigeration operates on

Brayton cycle

Reversed Carnot cycle

Carnot cycle

Rankine’s cycle

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

More or less depending on ambient conditions

Same

More

Less

36. The sub-cooling in a refrigeration cycle

None of these

Does not alter C.O.P.

Decreases C.O.P.

Increases C.O.P.

37. 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)

None of these

0.622 Pv / (Pb - Pv)

μ/[1 - (1 - μ) (Ps/Pb)]

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

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

Ammonia

Carbon dioxide

Sulphur dioxide

R-12

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

Water at 0°C

Mixture of ice and water under equilibrium conditions

Ice at 4°C

Solid and dry ice

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

Before passing through the condenser

After passing through the expansion or throttle valve

After passing through the condenser

Before entering the compressor

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

Compressor and condenser

Compressor and evaporator

Expansion valve and evaporator

Condenser and expansion valve

42. The superheating in a refrigeration cycle

Decreases C.O.P.

Increases C.O.P.

Does not alter C.O.P.

None of these

43. Ammonia absorption refrigeration cycle requires

Very little work input

Zero work input

Nearly same work input as for vapour compression cycle

Maximum work input

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

Relative

Specific

None of these

Absolute

45. The advantage of dry compression is that

It permits complete evaporation in the evaporator

It permits higher speeds to be used

All of the above

It results in high volumetric and mechanical efficiency

Refrigeration & Air-Conditioning Practice Set-4

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