Refrigeration & Air-Conditioning Practice Set-4

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

Ammonia

Sulphur dioxide

Carbon dioxide

R-12

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

Expansion valve and evaporator

Compressor and evaporator

Condenser and expansion valve

Compressor and condenser

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

Lower than

Same as

None of these

Higher than

4. 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 50% RH

20°C DBT and 60% RH

5. 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 remain unaffected

Will be lower

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

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

Indirect

Absorption

Direct

Compression

7. During cooling and dehumidification, dry bulb temperature

None of these

Remains constant

Decreases

Increases

8. Refrigeration in aeroplanes usually employs the following refrigerant

CO2

Air

Freon-22

Freon-11

9. 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

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

Wet vapour

Saturated liquid

Dry saturated vapour

Superheated vapour

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11. The specific humidity during heating and humidification process.

Increases

None of these

Decreases

Remains constant

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

Carbon dioxide

Sulphur dioxide

R-12

Ammonia

13. 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

3 kW

1 kW

2 kW

4 kW

14. 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 lies between the dry bulb and wet bulb temperatures of the 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

15. Superheating in a refrigeration cycle

C.O.P remains unaltered

Increases C.O.P

Decreases C.O.P

Other factors decide C.O.P

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

Effective temperature

Mean radiant temperature

None of these

Dew point temperature

17. The specific humidity during dehumidification process

Increases

Decreases

None of these

Remains constant

18. 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 - h2)/ (h1 - h2)

(hA - h1)/ (h2 - h1)

(h2 - hA)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

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

Heat of compression

Work done by compressor

Enthalpy increase in compressor

All of the above

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

Same

Less

More

More or less depending on ambient conditions

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21. Vapour compression refrigeration is somewhat like

Reversed Carnot cycle

None of the above

Carnot cycle

Rankine’s cycle

22. Moisture in Freon refrigeration system causes

Freezing automatic regulating valve

Corrosion of whole system

High power consumption

Ineffective refrigeration

23. The superheating in a refrigeration cycle

Does not alter C.O.P.

None of these

Increases C.O.P.

Decreases C.O.P.

24. The Freon group of refrigerants are

Zoetrope refrigerants

Inorganic refrigerants

Hydrocarbon refrigerants

Halocarbon refrigerants

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

After passing through the condenser

Before passing through the condenser

Before entering the compressor

After passing through the expansion or throttle valve

26. The sub-cooling in a refrigeration cycle

Increases C.O.P.

Decreases C.O.P.

Does not alter C.O.P.

None of these

27. 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

28. 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)

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

None of these

0.622 Pv / (Pb - Pv)

μ/[1 - (1 - μ) (Ps/Pb)]

29. Which of the following statement is correct?

The constant enthalpy lines are also constant wet bulb temperature lines

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

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

All of these

30. 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

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

Dry

None of these

Flooded

DX coil

32. Air refrigeration operates on

Brayton cycle

Reversed Carnot cycle

Carnot cycle

Rankine’s cycle

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

Small

Equal

High

Anything

34. 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

1.2

5

0.2

35. The advantage of dry compression is that

It permits complete evaporation in the evaporator

It permits higher speeds to be used

It results in high volumetric and mechanical efficiency

All of the above

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

CO2

NH3

Freon-22

Freon-12

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

All of these

Halide torch

Soap and water

Sulphur sticks

38. 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)

(td₂ - td₃)/(td₃ - td₁)

(td₃ - td₁)/(td₃ - td₂)

(td₃ - td₂)/(td₃ - td₁)

(td₃ - td₁)/(td₂ - td₃)

39. Air conditioning means

Cooling

All of these

Dehumidifying

Heating

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

Remain unaffected

May increase or decrease depending on the type of refrigerant used

Increase

Decrease

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41. During sensible cooling,

Relative humidity remains constant

Specific humidity increases

Partial pressure of vapour remains constant

Wet bulb temperature increases

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

Absolute

None of these

Specific

Relative

43. The relative coefficient of performance is

None of these

Actual COP × theoretical COP

Theoretical COP/actual COP

Actual COP/theoretical COP

44. Ammonia absorption refrigeration cycle requires

Nearly same work input as for vapour compression cycle

Very little work input

Zero work input

Maximum work input

45. 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 or equal to 3.65 kg

More than 10 kg

Less than 2 kg

Refrigeration & Air-Conditioning Practice Set-4

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