Refrigeration & Air-Conditioning Practice Set-4

Page 1 of 5

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

Compression of the refrigerant vapour

Evaporation of the refrigerant liquid

Metering of the refrigerant liquid

Condensation of the refrigerant vapour

2. 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

3. Moisture in Freon refrigeration system causes

Ineffective refrigeration

Corrosion of whole system

High power consumption

Freezing automatic regulating valve

4. 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 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

Of adiabatic saturation of incoming stream

5. 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)

(td₂ - td₃)/(td₃ - td₁)

(td₃ - td₁)/(td₃ - td₂)

6. Ammonia absorption refrigeration cycle requires

Maximum work input

Zero work input

Very little work input

Nearly same work input as for vapour compression cycle

7. Superheating in a refrigeration cycle

Decreases C.O.P

Other factors decide C.O.P

Increases C.O.P

C.O.P remains unaltered

8. 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

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

Will remain unaffected

9. The sub-cooling in a refrigeration cycle

Does not alter C.O.P.

Increases C.O.P.

None of these

Decreases C.O.P.

10. The advantage of dry compression is that

All of the above

It permits higher speeds to be used

It results in high volumetric and mechanical efficiency

It permits complete evaporation in the evaporator

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11. The superheating in a refrigeration cycle

Decreases C.O.P.

Increases C.O.P.

Does not alter C.O.P.

None of these

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

Lower than

Higher than

Same as

None of these

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

Ice at 4°C

Water at 0°C

Solid and dry ice

Mixture of ice and water under equilibrium conditions

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

Absorption

Indirect

Compression

Direct

15. 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

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

Ammonia

Sulphur dioxide

Carbon dioxide

R-12

17. The Freon group of refrigerants are

Halocarbon refrigerants

Zoetrope refrigerants

Inorganic refrigerants

Hydrocarbon refrigerants

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

Flooded

DX coil

None of these

Dry

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

Small

Equal

High

Anything

20. The specific humidity during heating and humidification process.

Remains constant

None of these

Decreases

Increases

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21. 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

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

Absolute

None of these

Specific

Relative

23. Air refrigeration operates on

Reversed Carnot cycle

Rankine’s cycle

Carnot cycle

Brayton cycle

24. 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

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

Wet vapour

Dry saturated vapour

Superheated vapour

Saturated liquid

26. During sensible cooling,

Wet bulb temperature increases

Partial pressure of vapour remains constant

Specific humidity increases

Relative humidity remains constant

27. 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)

None of these

μ/[1 - (1 - μ) (Ps/Pb)]

28. Refrigeration in aeroplanes usually employs the following refrigerant

Air

CO2

Freon-11

Freon-22

29. 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

6

1.2

0.2

5

30. 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

Mean radiant temperature

None of these

Page 4 of 5

31. 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)

32. During cooling and dehumidification, dry bulb temperature

Remains constant

Decreases

None of these

Increases

33. The specific humidity during dehumidification process

Decreases

None of these

Increases

Remains constant

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

Heat of compression

Work done by compressor

All of the above

Enthalpy increase in compressor

35. Vapour compression refrigeration is somewhat like

Reversed Carnot cycle

Rankine’s cycle

None of the above

Carnot cycle

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

R-12

Ammonia

Carbon dioxide

Sulphur dioxide

37. Air conditioning means

All of these

Dehumidifying

Heating

Cooling

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

Sulphur sticks

Soap and water

Halide torch

All of these

39. 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

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

CO2

Freon-22

Freon-12

NH3

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41. Which of the following statement is correct?

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

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

42. 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

2 kW

3 kW

4 kW

43. The relative coefficient of performance is

Actual COP/theoretical COP

Actual COP × theoretical COP

Theoretical COP/actual COP

None of these

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

20°C DBT and 60% RH

20°C DBT and 50% RH

26°C DBT and 60% RH

26°C DBT and 50% RH

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

Compressor and condenser

Condenser and expansion valve

Compressor and evaporator

Expansion valve and evaporator

Refrigeration & Air-Conditioning Practice Set-4

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