Refrigeration & Air-Conditioning Practice Set-4

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1. Which of the following statement is correct?

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

The constant enthalpy lines are also constant wet bulb temperature lines

2. 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

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

Compressor and evaporator

Expansion valve and evaporator

Condenser and expansion valve

Compressor and condenser

4. The relative coefficient of performance is

None of these

Theoretical COP/actual COP

Actual COP/theoretical COP

Actual COP × theoretical COP

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

Before entering the compressor

After passing through the expansion or throttle valve

Before passing through the condenser

After passing through the condenser

6. 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 10 kg

More than or equal to 3.65 kg

There is no such consideration

7. The specific humidity during heating and humidification process.

Increases

Remains constant

None of these

Decreases

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

Flooded

DX coil

Dry

None of these

9. 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

10. Ammonia absorption refrigeration cycle requires

Zero work input

Very little work input

Maximum work input

Nearly same work input as for vapour compression cycle

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11. The advantage of dry compression is that

It permits complete evaporation in the evaporator

It permits higher speeds to be used

It results in high volumetric and mechanical efficiency

All of the above

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

NH3

Freon-22

CO2

Freon-12

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

Relative

None of these

Absolute

Specific

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

Compression

Direct

Indirect

Absorption

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

Water at 0°C

Mixture of ice and water under equilibrium conditions

Solid and dry ice

Ice at 4°C

16. The sub-cooling in a refrigeration cycle

None of these

Increases C.O.P.

Decreases C.O.P.

Does not alter C.O.P.

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

R-12

Sulphur dioxide

Ammonia

Carbon dioxide

18. During cooling and dehumidification, dry bulb temperature

Remains constant

None of these

Increases

Decreases

19. 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

20. During sensible cooling,

Relative humidity remains constant

Wet bulb temperature increases

Partial pressure of vapour remains constant

Specific humidity increases

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

Anything

Small

Equal

High

22. The superheating in a refrigeration cycle

Decreases C.O.P.

Does not alter C.O.P.

None of these

Increases C.O.P.

23. 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)

0.622 Pv / (Pb - Pv)

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

None of these

μ/[1 - (1 - μ) (Ps/Pb)]

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

Remain unaffected

May increase or decrease depending on the type of refrigerant used

Decrease

Increase

25. Air refrigeration operates on

Reversed Carnot cycle

Rankine’s cycle

Carnot cycle

Brayton cycle

26. 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

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

All of the above

Heat of compression

Work done by compressor

Enthalpy increase in compressor

28. Vapour compression refrigeration is somewhat like

Reversed Carnot cycle

None of the above

Rankine’s cycle

Carnot cycle

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

Dry saturated vapour

Saturated liquid

Superheated vapour

Wet vapour

30. The Freon group of refrigerants are

Zoetrope refrigerants

Halocarbon refrigerants

Hydrocarbon refrigerants

Inorganic refrigerants

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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

5

6

0.2

1.2

32. The specific humidity during dehumidification process

Increases

Decreases

Remains constant

None of these

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

Effective temperature

None of these

Dew point temperature

Mean radiant temperature

34. Moisture in Freon refrigeration system causes

Corrosion of whole system

Freezing automatic regulating valve

Ineffective refrigeration

High power consumption

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

Evaporation of the refrigerant liquid

Metering of the refrigerant liquid

Condensation of the refrigerant vapour

Compression of the refrigerant vapour

36. Superheating in a refrigeration cycle

Other factors decide C.O.P

C.O.P remains unaltered

Decreases C.O.P

Increases C.O.P

37. Refrigeration in aeroplanes usually employs the following refrigerant

Freon-11

Air

Freon-22

CO2

38. 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

4 kW

2 kW

1 kW

3 kW

39. Air conditioning means

Heating

Dehumidifying

Cooling

All of these

40. 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 - td₁)/(td₂ - td₃)

(td₃ - td₂)/(td₃ - td₁)

(td₃ - td₁)/(td₃ - td₂)

(td₂ - td₃)/(td₃ - td₁)

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41. 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 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

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

Halide torch

All of these

Soap and water

Sulphur sticks

43. 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)

(h2 - hA)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

(hA - h1)/ (h2 - h1)

(hA - h2)/ (h1 - h2)

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

None of these

Same as

Higher than

Lower than

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

Ammonia

R-12

Sulphur dioxide

Carbon dioxide

Refrigeration & Air-Conditioning Practice Set-4

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