Refrigeration & Air-Conditioning Practice Set-4

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1. The advantage of dry compression is that

It permits complete evaporation in the evaporator

It results in high volumetric and mechanical efficiency

All of the above

It permits higher speeds to be used

2. 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 remain unaffected

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

Will be higher

3. Which of the following statement is correct?

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

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

4. The relative coefficient of performance is

Actual COP × theoretical COP

Theoretical COP/actual COP

Actual COP/theoretical COP

None of these

5. 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

1.2

6

0.2

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

More or less depending on ambient conditions

More

Less

Same

7. During sensible cooling,

Wet bulb temperature increases

Partial pressure of vapour remains constant

Specific humidity increases

Relative humidity remains constant

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

Dry saturated vapour

Wet vapour

Saturated liquid

Superheated vapour

9. 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

Effective temperature

None of these

10. Vapour compression refrigeration is somewhat like

None of the above

Rankine’s cycle

Carnot cycle

Reversed Carnot cycle

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

Same as

Lower than

Higher than

None of these

12. Refrigeration in aeroplanes usually employs the following refrigerant

Freon-22

Freon-11

Air

CO2

13. 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

3 kW

1 kW

2 kW

4 kW

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

20°C DBT and 50% RH

26°C DBT and 50% RH

20°C DBT and 60% RH

26°C DBT and 60% RH

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

Both room sensible heat and latent heat loads

Room latent heat load only

Room sensible heat load only

None of the above

16. 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

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

0.622 Pv / (Pb - Pv)

μ/[1 - (1 - μ) (Ps/Pb)]

17. 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)/(td₃ - td₂)

(td₃ - td₂)/(td₃ - td₁)

(td₃ - td₁)/(td₂ - td₃)

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

R-12

Carbon dioxide

Ammonia

Sulphur dioxide

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

Compression of the refrigerant vapour

Metering of the refrigerant liquid

Evaporation of the refrigerant liquid

Condensation of the refrigerant vapour

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

Absolute

Relative

None of these

Specific

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

After passing through the expansion or throttle valve

Before entering the compressor

Before passing through the condenser

After passing through the condenser

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

Condenser and expansion valve

Expansion valve and evaporator

Compressor and condenser

Compressor and evaporator

23. The specific humidity during dehumidification process

None of these

Increases

Remains constant

Decreases

24. 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

25. The specific humidity during heating and humidification process.

Decreases

Increases

Remains constant

None of these

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

More than 10 kg

Less than 2 kg

More than or equal to 3.65 kg

There is no such consideration

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

CO2

Freon-22

NH3

Freon-12

28. Moisture in Freon refrigeration system causes

Corrosion of whole system

High power consumption

Freezing automatic regulating valve

Ineffective refrigeration

29. During cooling and dehumidification, dry bulb temperature

Decreases

None of these

Increases

Remains constant

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

DX coil

Dry

Flooded

None of these

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31. The superheating in a refrigeration cycle

Decreases C.O.P.

Increases C.O.P.

Does not alter C.O.P.

None of these

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

Absorption

Indirect

Direct

Compression

33. The Freon group of refrigerants are

Inorganic refrigerants

Halocarbon refrigerants

Zoetrope refrigerants

Hydrocarbon refrigerants

34. Ammonia absorption refrigeration cycle requires

Maximum work input

Zero work input

Very little work input

Nearly same work input as for vapour compression cycle

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

Small

Anything

High

Equal

36. The sub-cooling in a refrigeration cycle

Increases C.O.P.

Does not alter C.O.P.

None of these

Decreases C.O.P.

37. 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

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

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

Ammonia

Sulphur dioxide

R-12

Carbon dioxide

39. 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)

(h1 - h2)/ (hA - h2)

(hA - h2)/ (h1 - h2)

(h2 - hA)/ (h1 - h2)

(hA - h1)/ (h2 - h1)

40. 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

Decrease

Increase

Remain unaffected

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41. Air conditioning means

Cooling

Heating

All of these

Dehumidifying

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

Soap and water

All of these

Halide torch

Sulphur sticks

43. Superheating in a refrigeration cycle

Increases C.O.P

Decreases C.O.P

Other factors decide C.O.P

C.O.P remains unaltered

44. 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

45. Air refrigeration operates on

Brayton cycle

Carnot cycle

Rankine’s cycle

Reversed Carnot cycle

Refrigeration & Air-Conditioning Practice Set-4

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