Refrigeration & Air-Conditioning Practice Set-4

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

Small

Equal

Anything

High

2. The specific humidity during dehumidification process

Decreases

Remains constant

None of these

Increases

3. The specific humidity during heating and humidification process.

Decreases

None of these

Remains constant

Increases

4. Ammonia absorption refrigeration cycle requires

Zero work input

Very little work input

Nearly same work input as for vapour compression cycle

Maximum work input

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

Specific

Relative

Absolute

None of these

6. Which of the following statement is correct?

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

The constant enthalpy lines are also constant wet bulb temperature lines

All of these

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

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

Direct

Absorption

Indirect

Compression

8. During cooling and dehumidification, dry bulb temperature

Increases

Remains constant

None of these

Decreases

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

Superheated vapour

Saturated liquid

Wet vapour

Dry saturated vapour

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

R-12

Carbon dioxide

Ammonia

Sulphur dioxide

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

Ice at 4°C

Water at 0°C

Mixture of ice and water under equilibrium conditions

Solid and dry ice

12. During sensible cooling,

Specific humidity increases

Wet bulb temperature increases

Partial pressure of vapour remains constant

Relative humidity remains constant

13. 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

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

Flooded

Dry

DX coil

None of these

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

Condenser and expansion valve

Compressor and condenser

Compressor and evaporator

Expansion valve and evaporator

16. The advantage of dry compression is that

It permits complete evaporation in the evaporator

It results in high volumetric and mechanical efficiency

It permits higher speeds to be used

All of the above

17. The sub-cooling in a refrigeration cycle

Increases C.O.P.

Does not alter C.O.P.

None of these

Decreases C.O.P.

18. The Freon group of refrigerants are

Zoetrope refrigerants

Halocarbon refrigerants

Inorganic refrigerants

Hydrocarbon refrigerants

19. 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

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

All of these

Soap and water

Halide torch

Sulphur sticks

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21. 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)]

22. 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)

(td₃ - td₁)/(td₂ - td₃)

(td₃ - td₂)/(td₃ - td₁)

(td₂ - td₃)/(td₃ - td₁)

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

NH3

Freon-22

CO2

Freon-12

24. 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

More than 10 kg

There is no such consideration

25. Superheating in a refrigeration cycle

Other factors decide C.O.P

Decreases C.O.P

C.O.P remains unaltered

Increases C.O.P

26. Moisture in Freon refrigeration system causes

High power consumption

Freezing automatic regulating valve

Corrosion of whole system

Ineffective refrigeration

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

26°C DBT and 50% RH

26°C DBT and 60% RH

20°C DBT and 60% RH

20°C DBT and 50% RH

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

Decrease

Remain unaffected

Increase

May increase or decrease depending on the type of refrigerant used

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

More

Same

More or less depending on ambient conditions

Less

30. Refrigeration in aeroplanes usually employs the following refrigerant

Freon-11

CO2

Air

Freon-22

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31. The relative coefficient of performance is

None of these

Actual COP × theoretical COP

Actual COP/theoretical COP

Theoretical COP/actual COP

32. The superheating in a refrigeration cycle

Decreases C.O.P.

Increases C.O.P.

Does not alter C.O.P.

None of these

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

Room sensible heat load only

Room latent heat load only

Both room sensible heat and latent heat loads

None of the above

34. Air conditioning means

Dehumidifying

All of these

Heating

Cooling

35. 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

1.2

0.2

6

5

36. Air refrigeration operates on

Brayton cycle

Carnot cycle

Rankine’s cycle

Reversed Carnot cycle

37. 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 higher

Will be lower

Will remain unaffected

38. Vapour compression refrigeration is somewhat like

None of the above

Rankine’s cycle

Reversed Carnot cycle

Carnot cycle

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)

(hA - h1)/ (h2 - h1)

(h2 - hA)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

(hA - h2)/ (h1 - h2)

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

Ammonia

Sulphur dioxide

R-12

Carbon dioxide

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

After passing through the expansion or throttle valve

Before passing through the condenser

After passing through the condenser

Before entering the compressor

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

Same as

Higher than

None of these

Lower than

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

Work done by compressor

All of the above

Heat of compression

Enthalpy increase in compressor

44. 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 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

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

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

Condensation of the refrigerant vapour

Compression of the refrigerant vapour

Evaporation of the refrigerant liquid

Metering of the refrigerant liquid

Refrigeration & Air-Conditioning Practice Set-4

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