Refrigeration & Air-Conditioning Practice Set-4

Page 1 of 5

1. 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

None of the above

Room sensible heat load only

2. The specific humidity during heating and humidification process.

Remains constant

Increases

Decreases

None of these

3. 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

None of these

Effective temperature

Mean radiant temperature

4. The relative coefficient of performance is

None of these

Actual COP × theoretical COP

Theoretical COP/actual COP

Actual COP/theoretical COP

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 - td₁)/(td₃ - td₂)

(td₂ - td₃)/(td₃ - td₁)

(td₃ - td₁)/(td₂ - td₃)

(td₃ - td₂)/(td₃ - td₁)

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

Halide torch

Soap and water

Sulphur sticks

All of these

7. The sub-cooling in a refrigeration cycle

Does not alter C.O.P.

None of these

Decreases C.O.P.

Increases C.O.P.

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

Lower than

Higher than

None of these

Same as

9. Ammonia absorption refrigeration cycle requires

Zero work input

Nearly same work input as for vapour compression cycle

Very little work input

Maximum work input

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

R-12

Ammonia

Carbon dioxide

Sulphur dioxide

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11. Refrigeration in aeroplanes usually employs the following refrigerant

CO2

Freon-22

Air

Freon-11

12. The superheating in a refrigeration cycle

Does not alter C.O.P.

Increases C.O.P.

Decreases C.O.P.

None of these

13. 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 - h1)/ (h2 - h1)

(h2 - hA)/ (h1 - h2)

(hA - h2)/ (h1 - h2)

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

Remain unaffected

Increase

Decrease

May increase or decrease depending on the type of refrigerant used

15. 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

16. Superheating in a refrigeration cycle

C.O.P remains unaltered

Decreases C.O.P

Other factors decide C.O.P

Increases C.O.P

17. 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 wet bulb and dew point 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 dry bulb and wet bulb temperatures of the incoming stream

18. 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

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

Wet vapour

Saturated liquid

Dry saturated vapour

Superheated vapour

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

Work done by compressor

Enthalpy increase in compressor

All of the above

Heat of compression

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21. 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

22. During sensible cooling,

Partial pressure of vapour remains constant

Relative humidity remains constant

Wet bulb temperature increases

Specific humidity increases

23. Air conditioning means

Dehumidifying

Heating

Cooling

All of these

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

Carbon dioxide

Ammonia

Sulphur dioxide

R-12

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

NH3

CO2

Freon-22

Freon-12

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

Same

Less

More or less depending on ambient conditions

More

27. 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

0.2

1.2

5

28. Vapour compression refrigeration is somewhat like

None of the above

Rankine’s cycle

Carnot cycle

Reversed Carnot cycle

29. Moisture in Freon refrigeration system causes

Freezing automatic regulating valve

Ineffective refrigeration

High power consumption

Corrosion of whole system

30. 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

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

Relative

Specific

Absolute

None of these

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

Compressor and condenser

Expansion valve and evaporator

Condenser and expansion valve

Compressor and evaporator

33. 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

3 kW

2 kW

4 kW

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

Indirect

Direct

Absorption

Compression

35. The specific humidity during dehumidification process

Decreases

Remains constant

None of these

Increases

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

26°C DBT and 60% RH

20°C DBT and 60% RH

20°C DBT and 50% RH

26°C DBT and 50% RH

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

Dry

None of these

Flooded

DX coil

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

Metering of the refrigerant liquid

Evaporation of the refrigerant liquid

Condensation of the refrigerant vapour

Compression of the refrigerant vapour

39. 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)

μ/[1 - (1 - μ) (Ps/Pb)]

None of these

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

40. Which of the following statement is correct?

The constant enthalpy lines are also constant wet bulb temperature lines

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

All of these

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

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

Equal

Anything

Small

High

42. Air refrigeration operates on

Reversed Carnot cycle

Brayton cycle

Carnot cycle

Rankine’s cycle

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

Solid and dry ice

Water at 0°C

Ice at 4°C

Mixture of ice and water under equilibrium conditions

44. During cooling and dehumidification, dry bulb temperature

Decreases

Increases

Remains constant

None of these

45. The Freon group of refrigerants are

Halocarbon refrigerants

Hydrocarbon refrigerants

Zoetrope refrigerants

Inorganic refrigerants

Refrigeration & Air-Conditioning Practice Set-4

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