Refrigeration & Air-Conditioning Practice Set-4

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

R-12

Ammonia

Carbon dioxide

Sulphur dioxide

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

None of the above

Both room sensible heat and latent heat loads

Room sensible heat load only

Room latent heat load only

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

Same as

Higher than

None of these

Lower than

4. The advantage of dry compression is that

It permits higher speeds to be used

It permits complete evaporation in the evaporator

All of the above

It results in high volumetric and mechanical efficiency

5. 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)

(h2 - hA)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

6. 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

7. 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)

None of these

0.622 Pv / (Pb - Pv)

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

μ/[1 - (1 - μ) (Ps/Pb)]

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

Compression of the refrigerant vapour

Condensation of the refrigerant vapour

Metering of the refrigerant liquid

Evaporation of the refrigerant liquid

9. 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 remain unaffected

Will be lower

Will be higher

10. During cooling and dehumidification, dry bulb temperature

None of these

Decreases

Increases

Remains constant

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

Absorption

Indirect

Direct

Compression

12. The specific humidity during dehumidification process

Increases

Remains constant

None of these

Decreases

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

Condenser and expansion valve

Compressor and evaporator

Expansion valve and evaporator

Compressor and condenser

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

Wet vapour

Superheated vapour

Saturated liquid

Dry saturated vapour

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

Equal

Small

Anything

High

16. Air conditioning means

All of these

Heating

Cooling

Dehumidifying

17. Refrigeration in aeroplanes usually employs the following refrigerant

Freon-11

Air

CO2

Freon-22

18. 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

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

None of these

Relative

Absolute

Specific

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

Ammonia

R-12

Carbon dioxide

Sulphur dioxide

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21. Vapour compression refrigeration is somewhat like

Carnot cycle

Reversed Carnot cycle

Rankine’s cycle

None of the above

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)

(td₂ - td₃)/(td₃ - td₁)

(td₃ - td₁)/(td₂ - td₃)

(td₃ - td₂)/(td₃ - td₁)

(td₃ - td₁)/(td₃ - td₂)

23. 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

6

1.2

5

24. 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

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

Halide torch

All of these

Soap and water

Sulphur sticks

26. The specific humidity during heating and humidification process.

Remains constant

Increases

Decreases

None of these

27. During sensible cooling,

Partial pressure of vapour remains constant

Wet bulb temperature increases

Specific humidity increases

Relative humidity remains constant

28. The sub-cooling in a refrigeration cycle

Does not alter C.O.P.

Increases C.O.P.

Decreases C.O.P.

None of these

29. 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

Effective temperature

Dew point temperature

None of these

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

After passing through the condenser

Before passing through the condenser

After passing through the expansion or throttle valve

Before entering the compressor

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31. In order to cool and dehumidify a stream of moist air, it must be passed over the coil at a temperature

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

Of adiabatic saturation of incoming stream

32. Moisture in Freon refrigeration system causes

Freezing automatic regulating valve

High power consumption

Ineffective refrigeration

Corrosion of whole system

33. 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

34. The Freon group of refrigerants are

Halocarbon refrigerants

Inorganic refrigerants

Zoetrope refrigerants

Hydrocarbon refrigerants

35. 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

36. The superheating in a refrigeration cycle

None of these

Does not alter C.O.P.

Increases C.O.P.

Decreases C.O.P.

37. Air refrigeration operates on

Brayton cycle

Rankine’s cycle

Carnot cycle

Reversed Carnot cycle

38. 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

2 kW

1 kW

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

None of these

DX coil

Flooded

Dry

40. Ammonia absorption refrigeration cycle requires

Nearly same work input as for vapour compression cycle

Zero work input

Maximum work input

Very little work input

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41. The relative coefficient of performance is

Actual COP/theoretical COP

None of these

Theoretical COP/actual COP

Actual COP × theoretical COP

42. 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

There is no such consideration

Less than 2 kg

43. 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

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

NH3

Freon-12

Freon-22

CO2

45. Superheating in a refrigeration cycle

Increases C.O.P

C.O.P remains unaltered

Other factors decide C.O.P

Decreases C.O.P

Refrigeration & Air-Conditioning Practice Set-4

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