Refrigeration & Air-Conditioning Practice Set-4

Page 1 of 5

1. Vapour compression refrigeration is somewhat like

Carnot cycle

Reversed Carnot cycle

Rankine’s cycle

None of the above

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

Solid and dry ice

Water at 0°C

Mixture of ice and water under equilibrium conditions

Ice at 4°C

3. Air conditioning means

Dehumidifying

Cooling

Heating

All of these

4. Superheating in a refrigeration cycle

Decreases C.O.P

Other factors decide C.O.P

Increases C.O.P

C.O.P remains unaltered

5. 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

4 kW

1 kW

3 kW

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

None of these

Absolute

Specific

Relative

7. During sensible cooling,

Relative humidity remains constant

Partial pressure of vapour remains constant

Wet bulb temperature increases

Specific humidity increases

8. Ammonia absorption refrigeration cycle requires

Zero work input

Very little work input

Maximum work input

Nearly same work input as for vapour compression cycle

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

Small

Equal

High

Anything

10. Which of the following statement is correct?

All of these

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

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

Evaporation of the refrigerant liquid

Condensation of the refrigerant vapour

Compression of the refrigerant vapour

Metering of the refrigerant liquid

12. The superheating in a refrigeration cycle

Does not alter C.O.P.

Increases C.O.P.

None of these

Decreases C.O.P.

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

Indirect

Compression

Absorption

Direct

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

Increase

Remain unaffected

Decrease

May increase or decrease depending on the type of refrigerant used

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

20°C DBT and 50% RH

26°C DBT and 50% RH

26°C DBT and 60% RH

20°C DBT and 60% RH

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

Expansion valve and evaporator

Compressor and evaporator

Condenser and expansion valve

Compressor and condenser

17. The specific humidity during dehumidification process

Decreases

Increases

Remains constant

None of these

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

Freon-22

CO2

Freon-12

NH3

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

Dry saturated vapour

Wet vapour

Saturated liquid

Superheated vapour

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

Same as

None of these

Higher than

Lower than

Page 3 of 5

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

Enthalpy increase in compressor

Work done by compressor

Heat of compression

All of the above

22. 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 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

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

Ammonia

Sulphur dioxide

Carbon dioxide

R-12

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

After passing through the condenser

Before passing through the condenser

Before entering the compressor

After passing through the expansion or throttle valve

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

More

Less

Same

More or less depending on ambient conditions

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

Ammonia

Carbon dioxide

R-12

Sulphur dioxide

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

Soap and water

Sulphur sticks

Halide torch

All 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)

(hA - h1)/ (h2 - h1)

(hA - h2)/ (h1 - h2)

(h2 - hA)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

29. The Freon group of refrigerants are

Inorganic refrigerants

Halocarbon refrigerants

Zoetrope refrigerants

Hydrocarbon refrigerants

30. The advantage of dry compression is that

It results in high volumetric and mechanical efficiency

All of the above

It permits complete evaporation in the evaporator

It permits higher speeds to be used

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31. 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

1.2

5

32. Moisture in Freon refrigeration system causes

Freezing automatic regulating valve

Ineffective refrigeration

Corrosion of whole system

High power consumption

33. Air refrigeration operates on

Rankine’s cycle

Brayton cycle

Reversed Carnot cycle

Carnot cycle

34. During cooling and dehumidification, dry bulb temperature

Decreases

Remains constant

None of these

Increases

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

More than 10 kg

There is no such consideration

More than or equal to 3.65 kg

Less than 2 kg

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,

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

Will be lower

Will be higher

Will remain unaffected

37. The specific humidity during heating and humidification process.

Increases

Decreases

None of these

Remains constant

38. The sub-cooling in a refrigeration cycle

Decreases C.O.P.

Increases C.O.P.

Does not alter C.O.P.

None of these

39. 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

Room latent heat load only

None of the above

40. Refrigeration in aeroplanes usually employs the following refrigerant

Freon-11

CO2

Air

Freon-22

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41. 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

μ/[1 - (1 - μ) (Ps/Pb)]

0.622 Pv / (Pb - Pv)

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

42. The relative coefficient of performance is

Actual COP × theoretical COP

Actual COP/theoretical COP

Theoretical COP/actual COP

None of these

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

Dew point temperature

Mean radiant temperature

None of these

Effective temperature

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

DX coil

Flooded

Dry

None of these

45. 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)

(td₂ - td₃)/(td₃ - td₁)

(td₃ - td₁)/(td₂ - td₃)

Refrigeration & Air-Conditioning Practice Set-4

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