Refrigeration & Air-Conditioning Practice Set-4

Page 1 of 5

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

Soap and water

Sulphur sticks

Halide torch

All of these

2. 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)

(h2 - hA)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

3. Refrigeration in aeroplanes usually employs the following refrigerant

Freon-11

Air

CO2

Freon-22

4. 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)/(td₃ - td₂)

(td₃ - td₁)/(td₂ - td₃)

(td₂ - td₃)/(td₃ - td₁)

5. 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

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

Decrease

Remain unaffected

May increase or decrease depending on the type of refrigerant used

Increase

7. 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

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

Less

Same

More or less depending on ambient conditions

More

9. Which of the following statement is correct?

The constant enthalpy lines are also constant wet bulb temperature lines

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

10. Air refrigeration operates on

Brayton cycle

Rankine’s cycle

Reversed Carnot cycle

Carnot cycle

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

Indirect

Direct

Absorption

Compression

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 higher

Will be lower

Will remain unaffected

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

13. Ammonia absorption refrigeration cycle requires

Maximum work input

Very little work input

Zero work input

Nearly same work input as for vapour compression cycle

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

Compression of the refrigerant vapour

Condensation of the refrigerant vapour

Evaporation of the refrigerant liquid

Metering of the refrigerant liquid

15. Moisture in Freon refrigeration system causes

Corrosion of whole system

Ineffective refrigeration

Freezing automatic regulating valve

High power consumption

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

CO2

NH3

Freon-22

Freon-12

17. During sensible cooling,

Wet bulb temperature increases

Specific humidity increases

Partial pressure of vapour remains constant

Relative humidity remains constant

18. Vapour compression refrigeration is somewhat like

None of the above

Reversed Carnot cycle

Rankine’s cycle

Carnot cycle

19. 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)

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

μ/[1 - (1 - μ) (Ps/Pb)]

20. 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

Effective temperature

Mean radiant temperature

Dew point temperature

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21. Superheating in a refrigeration cycle

Other factors decide C.O.P

C.O.P remains unaltered

Decreases C.O.P

Increases C.O.P

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

Dry

None of these

Flooded

DX coil

23. During cooling and dehumidification, dry bulb temperature

Remains constant

None of these

Increases

Decreases

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

Compressor and condenser

Expansion valve and evaporator

Compressor and evaporator

Condenser and expansion valve

25. Air conditioning means

Dehumidifying

All of these

Heating

Cooling

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

Wet vapour

Superheated vapour

Saturated liquid

Dry saturated vapour

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

None of the above

Room latent heat load only

Both room sensible heat and latent heat loads

Room sensible heat load only

28. The specific humidity during dehumidification process

Increases

None of these

Decreases

Remains constant

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

Before entering the compressor

After passing through the expansion or throttle valve

After passing through the condenser

Before passing through the condenser

30. 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

Page 4 of 5

31. In order to cool and dehumidify a stream of moist air, it must be passed over the coil at a temperature

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

Which lies between the wet bulb and dew point temperatures of the incoming stream

Of adiabatic saturation of incoming stream

32. The superheating in a refrigeration cycle

Increases C.O.P.

Decreases C.O.P.

None of these

Does not alter C.O.P.

33. 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

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

Relative

Absolute

None of these

Specific

35. The sub-cooling in a refrigeration cycle

None of these

Increases C.O.P.

Does not alter C.O.P.

Decreases C.O.P.

36. The relative coefficient of performance is

None of these

Theoretical COP/actual COP

Actual COP/theoretical COP

Actual COP × theoretical COP

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

R-12

Carbon dioxide

Ammonia

Sulphur dioxide

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

Small

Anything

High

Equal

39. 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

1 kW

4 kW

3 kW

40. 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 60% RH

26°C DBT and 50% RH

Page 5 of 5

41. The Freon group of refrigerants are

Halocarbon refrigerants

Hydrocarbon refrigerants

Zoetrope refrigerants

Inorganic refrigerants

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

Same as

Higher than

Lower than

None of these

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

R-12

Ammonia

Sulphur dioxide

Carbon dioxide

44. The specific humidity during heating and humidification process.

Decreases

Increases

None of these

Remains constant

45. 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

6

5

Refrigeration & Air-Conditioning Practice Set-4

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