Refrigeration & Air-Conditioning Practice Set-4

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1. 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

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

Absorption

Direct

Compression

Indirect

3. Vapour compression refrigeration is somewhat like

Carnot cycle

Reversed Carnot cycle

Rankine’s cycle

None of the above

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

Sulphur dioxide

Ammonia

R-12

Carbon dioxide

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)

(td₃ - td₂)/(td₃ - td₁)

(td₂ - td₃)/(td₃ - td₁)

(td₃ - td₁)/(td₂ - td₃)

6. The relative coefficient of performance is

Actual COP/theoretical COP

Theoretical COP/actual COP

Actual COP × theoretical COP

None of these

7. 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

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

More than or equal to 3.65 kg

More than 10 kg

Less than 2 kg

There is no such consideration

9. 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

1.2

6

5

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

Same as

Lower than

Higher than

None of these

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

Room latent heat load only

None of the above

Both room sensible heat and latent heat loads

Room sensible heat load only

12. The sub-cooling in a refrigeration cycle

Does not alter C.O.P.

Decreases C.O.P.

Increases C.O.P.

None of these

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

Dry

None of these

Flooded

DX coil

14. 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)]

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

Anything

Equal

High

Small

16. 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

3 kW

1 kW

2 kW

17. The specific humidity during heating and humidification process.

None of these

Increases

Decreases

Remains constant

18. The specific humidity during dehumidification process

Decreases

None of these

Remains constant

Increases

19. 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)

(hA - h2)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

(h2 - hA)/ (h1 - h2)

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

Expansion valve and evaporator

Compressor and condenser

Condenser and expansion valve

Compressor and evaporator

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21. Air refrigeration operates on

Rankine’s cycle

Carnot cycle

Reversed Carnot cycle

Brayton cycle

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

Condensation of the refrigerant vapour

Compression of the refrigerant vapour

Metering of the refrigerant liquid

Evaporation of the refrigerant liquid

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

All of these

Soap and water

Halide torch

Sulphur sticks

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

None of these

Absolute

Specific

Relative

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

Heat of compression

All of the above

Work done by compressor

Enthalpy increase in compressor

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

Less

More or less depending on ambient conditions

Same

More

27. Refrigeration in aeroplanes usually employs the following refrigerant

Freon-11

Air

Freon-22

CO2

28. During cooling and dehumidification, dry bulb temperature

Remains constant

None of these

Increases

Decreases

29. 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

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

Dry saturated vapour

Wet vapour

Superheated vapour

Saturated liquid

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31. Moisture in Freon refrigeration system causes

Corrosion of whole system

Ineffective refrigeration

High power consumption

Freezing automatic regulating valve

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

Ammonia

Carbon dioxide

R-12

Sulphur dioxide

33. Superheating in a refrigeration cycle

Other factors decide C.O.P

C.O.P remains unaltered

Increases C.O.P

Decreases C.O.P

34. Ammonia absorption refrigeration cycle requires

Zero work input

Very little work input

Maximum work input

Nearly same work input as for vapour compression cycle

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

Freon-22

NH3

Freon-12

CO2

36. Air conditioning means

Cooling

Heating

Dehumidifying

All of these

37. The Freon group of refrigerants are

Halocarbon refrigerants

Inorganic refrigerants

Zoetrope refrigerants

Hydrocarbon refrigerants

38. The superheating in a refrigeration cycle

Decreases C.O.P.

Does not alter C.O.P.

Increases C.O.P.

None of these

39. 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

Increase

Decrease

Remain unaffected

40. During sensible cooling,

Wet bulb temperature increases

Relative humidity remains constant

Partial pressure of vapour remains constant

Specific humidity increases

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

Ice at 4°C

Solid and dry ice

Water at 0°C

Mixture of ice and water under equilibrium conditions

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

After passing through the condenser

Before entering the compressor

After passing through the expansion or throttle valve

Before passing through the condenser

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

Mean radiant temperature

None of these

Dew point temperature

Effective temperature

44. 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

Will remain unaffected

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

45. 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

Refrigeration & Air-Conditioning Practice Set-4

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