Refrigeration & Air-Conditioning Practice Set-4

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1. During sensible cooling,

Partial pressure of vapour remains constant

Relative humidity remains constant

Specific humidity increases

Wet bulb temperature increases

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

Direct

Absorption

Indirect

Compression

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

Dry

None of these

DX coil

Flooded

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

Before entering the compressor

After passing through the expansion or throttle valve

Before passing through the condenser

After passing through the condenser

5. Ammonia absorption refrigeration cycle requires

Nearly same work input as for vapour compression cycle

Zero work input

Very little work input

Maximum work input

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

Equal

Small

High

Anything

7. Moisture in Freon refrigeration system causes

Freezing automatic regulating valve

Ineffective refrigeration

Corrosion of whole system

High power consumption

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

More than 10 kg

More than or equal to 3.65 kg

Less than 2 kg

There is no such consideration

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

All of the above

Heat of compression

Work done by compressor

Enthalpy increase in compressor

10. 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

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11. 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

Remain unaffected

Decrease

Increase

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

R-12

Carbon dioxide

Sulphur dioxide

Ammonia

13. Air refrigeration operates on

Brayton cycle

Rankine’s cycle

Reversed Carnot cycle

Carnot cycle

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

Compression of the refrigerant vapour

Evaporation of the refrigerant liquid

Metering of the refrigerant liquid

Condensation of the refrigerant vapour

15. The sub-cooling in a refrigeration cycle

Decreases C.O.P.

Increases C.O.P.

None of these

Does not alter C.O.P.

16. 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)

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

None of these

μ/[1 - (1 - μ) (Ps/Pb)]

17. Vapour compression refrigeration is somewhat like

Reversed Carnot cycle

Rankine’s cycle

Carnot cycle

None of the above

18. Refrigeration in aeroplanes usually employs the following refrigerant

Freon-11

CO2

Freon-22

Air

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

NH3

Freon-12

Freon-22

CO2

20. 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

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

Soap and water

Halide torch

All of these

Sulphur sticks

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

Same as

Lower than

Higher than

None of these

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

Dry saturated vapour

Superheated vapour

Wet vapour

Saturated liquid

24. 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

25. The superheating in a refrigeration cycle

Does not alter C.O.P.

Increases C.O.P.

Decreases C.O.P.

None of these

26. Air conditioning means

Cooling

Dehumidifying

Heating

All of these

27. 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

28. 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 be higher

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

Will remain unaffected

29. 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 - td₂)/(td₃ - td₁)

(td₃ - td₁)/(td₃ - td₂)

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

Carbon dioxide

Sulphur dioxide

R-12

Ammonia

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

Specific

None of these

Relative

Absolute

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

Mixture of ice and water under equilibrium conditions

Ice at 4°C

Water at 0°C

Solid and dry ice

33. 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)

(h1 - h2)/ (hA - h2)

(h2 - hA)/ (h1 - h2)

(hA - h2)/ (h1 - h2)

(hA - h1)/ (h2 - h1)

34. During cooling and dehumidification, dry bulb temperature

Decreases

Remains constant

Increases

None of these

35. The relative coefficient of performance is

Actual COP × theoretical COP

Actual COP/theoretical COP

None of these

Theoretical COP/actual COP

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

Less

More

Same

More or less depending on ambient conditions

37. Superheating in a refrigeration cycle

C.O.P remains unaltered

Other factors decide C.O.P

Increases C.O.P

Decreases C.O.P

38. 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

None of these

Effective temperature

Mean radiant temperature

39. The specific humidity during dehumidification process

None of these

Decreases

Remains constant

Increases

40. 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

5

6

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

Compressor and evaporator

Compressor and condenser

Expansion valve and evaporator

Condenser and expansion valve

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

26°C DBT and 50% RH

20°C DBT and 50% RH

26°C DBT and 60% RH

20°C DBT and 60% RH

43. Which of the following statement is correct?

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

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

44. The specific humidity during heating and humidification process.

None of these

Increases

Decreases

Remains constant

45. The Freon group of refrigerants are

Hydrocarbon refrigerants

Inorganic refrigerants

Halocarbon refrigerants

Zoetrope refrigerants

Refrigeration & Air-Conditioning Practice Set-4

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