Refrigeration & Air-Conditioning Practice Set-4

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

After passing through the expansion or throttle valve

After passing through the condenser

Before entering the compressor

Before passing through the condenser

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

Saturated liquid

Superheated vapour

Wet vapour

Dry saturated vapour

3. Air refrigeration operates on

Rankine’s cycle

Brayton cycle

Carnot cycle

Reversed Carnot cycle

4. 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

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

Will be higher

Will remain unaffected

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

20°C DBT and 60% RH

20°C DBT and 50% RH

26°C DBT and 50% RH

26°C DBT and 60% RH

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

More than 10 kg

Less than 2 kg

There is no such consideration

More than or equal to 3.65 kg

7. Which of the following statement is correct?

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

All of these

The constant enthalpy lines are also constant wet bulb temperature lines

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

8. Air conditioning means

Dehumidifying

Cooling

Heating

All of these

9. The advantage of dry compression is that

It permits higher speeds to be used

It results in high volumetric and mechanical efficiency

All of the above

It permits complete evaporation in the evaporator

10. Refrigeration in aeroplanes usually employs the following refrigerant

Freon-22

Freon-11

Air

CO2

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

Same

More

More or less depending on ambient conditions

Less

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

Carbon dioxide

Ammonia

R-12

Sulphur dioxide

13. Vapour compression refrigeration is somewhat like

None of the above

Reversed Carnot cycle

Rankine’s cycle

Carnot cycle

14. 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

Dew point temperature

None of these

Effective temperature

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

Condenser and expansion valve

Compressor and evaporator

Expansion valve and evaporator

Compressor and condenser

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

Sulphur dioxide

R-12

Ammonia

Carbon dioxide

17. The specific humidity during dehumidification process

Remains constant

Decreases

Increases

None of these

18. 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)

None of these

μ/[1 - (1 - μ) (Ps/Pb)]

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

19. Superheating in a refrigeration cycle

Other factors decide C.O.P

Decreases C.O.P

Increases C.O.P

C.O.P remains unaltered

20. 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)

(hA - h2)/ (h1 - h2)

(hA - h1)/ (h2 - h1)

(h1 - h2)/ (hA - h2)

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21. 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)

(td₂ - td₃)/(td₃ - td₁)

(td₃ - td₁)/(td₃ - td₂)

(td₃ - td₂)/(td₃ - td₁)

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

Absolute

None of these

Relative

Specific

23. 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

2 kW

4 kW

1 kW

3 kW

24. Ammonia absorption refrigeration cycle requires

Nearly same work input as for vapour compression cycle

Maximum work input

Zero work input

Very little work input

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

Compression

Direct

Absorption

Indirect

26. 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

1.2

0.2

27. The superheating in a refrigeration cycle

Does not alter C.O.P.

None of these

Decreases C.O.P.

Increases C.O.P.

28. During sensible cooling,

Partial pressure of vapour remains constant

Relative humidity remains constant

Specific humidity increases

Wet bulb temperature increases

29. The relative coefficient of performance is

Actual COP/theoretical COP

None of these

Actual COP × theoretical COP

Theoretical COP/actual COP

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

Halide torch

Soap and water

All of these

Sulphur sticks

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

Same as

Lower than

None of these

Higher than

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

Small

High

Equal

Anything

33. Moisture in Freon refrigeration system causes

Ineffective refrigeration

Corrosion of whole system

Freezing automatic regulating valve

High power consumption

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

None of the above

Room latent heat load only

Room sensible heat load only

Both room sensible heat and latent heat loads

35. During cooling and dehumidification, dry bulb temperature

Increases

Remains constant

None of these

Decreases

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

All of the above

Enthalpy increase in compressor

Work done by compressor

Heat of compression

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

Freon-22

Freon-12

CO2

NH3

38. The sub-cooling in a refrigeration cycle

None of these

Increases C.O.P.

Does not alter C.O.P.

Decreases C.O.P.

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

Metering of the refrigerant liquid

Condensation of the refrigerant vapour

Compression of the refrigerant vapour

Evaporation of the refrigerant liquid

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

None of these

DX coil

Dry

Flooded

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41. The specific humidity during heating and humidification process.

Decreases

Increases

None of these

Remains constant

42. 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

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

Of adiabatic saturation of incoming stream

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

Ice at 4°C

Mixture of ice and water under equilibrium conditions

Solid and dry ice

Water at 0°C

44. The Freon group of refrigerants are

Zoetrope refrigerants

Halocarbon refrigerants

Hydrocarbon refrigerants

Inorganic refrigerants

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

Increase

Decrease

May increase or decrease depending on the type of refrigerant used

Remain unaffected

Refrigeration & Air-Conditioning Practice Set-4

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