Refrigeration & Air-Conditioning Practice Set-4

Page 1 of 5

1. During sensible cooling,

Relative humidity remains constant

Partial pressure of vapour remains constant

Wet bulb temperature increases

Specific humidity increases

2. Air conditioning means

Cooling

Dehumidifying

All of these

Heating

3. Ammonia absorption refrigeration cycle requires

Zero work input

Maximum work input

Very little work input

Nearly same work input as for vapour compression cycle

4. The specific humidity during heating and humidification process.

None of these

Increases

Decreases

Remains constant

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

Equal

Small

High

Anything

6. 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

5

6

1.2

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

There is no such consideration

More than 10 kg

More than or equal to 3.65 kg

Less than 2 kg

8. 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

9. In order to cool and dehumidify a stream of moist air, it must be passed over the coil at a temperature

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

Of adiabatic saturation of incoming stream

Which lies between the dry bulb and wet bulb temperatures of the incoming stream

10. The relative coefficient of performance is

Actual COP × theoretical COP

Actual COP/theoretical COP

Theoretical COP/actual COP

None of these

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

Absorption

Compression

Indirect

Direct

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

Dry saturated vapour

Saturated liquid

Superheated vapour

Wet vapour

13. 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

14. Vapour compression refrigeration is somewhat like

Reversed Carnot cycle

None of the above

Rankine’s cycle

Carnot cycle

15. 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

16. 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

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

Ammonia

Sulphur dioxide

R-12

Carbon dioxide

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

Metering of the refrigerant liquid

Evaporation of the refrigerant liquid

Compression of the refrigerant vapour

Condensation of the refrigerant vapour

19. Moisture in Freon refrigeration system causes

High power consumption

Ineffective refrigeration

Corrosion of whole system

Freezing automatic regulating valve

20. Refrigeration in aeroplanes usually employs the following refrigerant

Freon-11

CO2

Freon-22

Air

Page 3 of 5

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

Dry

Flooded

None of these

DX coil

22. Superheating in a refrigeration cycle

Decreases C.O.P

C.O.P remains unaltered

Increases C.O.P

Other factors decide C.O.P

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

Before entering the compressor

Before passing through the condenser

After passing through the expansion or throttle valve

After passing through the condenser

24. 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

Will be higher

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

25. The sub-cooling in a refrigeration cycle

Does not alter C.O.P.

Increases C.O.P.

Decreases C.O.P.

None of these

26. 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)

μ/[1 - (1 - μ) (Ps/Pb)]

None of these

0.622 Pv / (Pb - Pv)

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

27. Which of the following statement is correct?

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

All of these

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

The constant enthalpy lines are also constant wet bulb temperature lines

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

Relative

Specific

None of these

Absolute

29. The advantage of dry compression is that

It permits complete evaporation in the evaporator

All of the above

It results in high volumetric and mechanical efficiency

It permits higher speeds to be used

30. 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)

(h2 - hA)/ (h1 - h2)

(hA - h2)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

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

Ammonia

R-12

Sulphur dioxide

Carbon dioxide

32. During cooling and dehumidification, dry bulb temperature

Decreases

Increases

None of these

Remains constant

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

Room latent heat load only

Both room sensible heat and latent heat loads

None of the above

Room sensible heat load only

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

Soap and water

All of these

Halide torch

Sulphur sticks

35. Air refrigeration operates on

Rankine’s cycle

Brayton cycle

Reversed Carnot cycle

Carnot cycle

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

Expansion valve and evaporator

Condenser and expansion valve

Compressor and condenser

Compressor and evaporator

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

Lower than

None of these

Same as

Higher than

38. The specific humidity during dehumidification process

Remains constant

Increases

None of these

Decreases

39. The Freon group of refrigerants are

Hydrocarbon refrigerants

Zoetrope refrigerants

Halocarbon refrigerants

Inorganic refrigerants

40. The superheating in a refrigeration cycle

Does not alter C.O.P.

None of these

Decreases C.O.P.

Increases C.O.P.

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41. 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)

42. 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

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

Freon-12

NH3

Freon-22

CO2

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

26°C DBT and 60% RH

20°C DBT and 60% RH

26°C DBT and 50% RH

20°C DBT and 50% RH

45. 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

Refrigeration & Air-Conditioning Practice Set-4

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