Refrigeration & Air-Conditioning Practice Set-4

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

Solid and dry ice

Ice at 4°C

Mixture of ice and water under equilibrium conditions

Water at 0°C

2. 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)

(h2 - hA)/ (h1 - h2)

(hA - h2)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

3. Refrigeration in aeroplanes usually employs the following refrigerant

Freon-11

Air

CO2

Freon-22

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

Metering of the refrigerant liquid

Condensation of the refrigerant vapour

Evaporation of the refrigerant liquid

Compression of the refrigerant vapour

5. Air refrigeration operates on

Carnot cycle

Brayton cycle

Rankine’s cycle

Reversed Carnot cycle

6. Vapour compression refrigeration is somewhat like

Reversed Carnot cycle

Carnot cycle

Rankine’s cycle

None of the above

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

Halide torch

Sulphur sticks

Soap and water

All of these

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

Decrease

Remain unaffected

Increase

May increase or decrease depending on the type of refrigerant used

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

DX coil

Dry

Flooded

None of these

10. 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)

μ/[1 - (1 - μ) (Ps/Pb)]

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

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

Freon-12

CO2

NH3

Freon-22

12. Which of the following statement is correct?

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

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

The constant enthalpy lines are also constant wet bulb temperature lines

All of these

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

More

Less

More or less depending on ambient conditions

Same

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

Relative

Specific

Absolute

None of these

15. The relative coefficient of performance is

None of these

Actual COP/theoretical COP

Theoretical COP/actual COP

Actual COP × theoretical COP

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

Work done by compressor

All of the above

Heat of compression

Enthalpy increase in compressor

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

20°C DBT and 60% RH

26°C DBT and 60% RH

20°C DBT and 50% RH

26°C DBT and 50% RH

18. The specific humidity during heating and humidification process.

None of these

Decreases

Remains constant

Increases

19. Air conditioning means

Cooling

Heating

Dehumidifying

All of these

20. During sensible cooling,

Specific humidity increases

Relative humidity remains constant

Partial pressure of vapour remains constant

Wet bulb temperature increases

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21. 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

0.2

1.2

22. The superheating in a refrigeration cycle

Decreases C.O.P.

None of these

Increases C.O.P.

Does not alter C.O.P.

23. The Freon group of refrigerants are

Inorganic refrigerants

Hydrocarbon refrigerants

Halocarbon refrigerants

Zoetrope refrigerants

24. During cooling and dehumidification, dry bulb temperature

None of these

Decreases

Increases

Remains constant

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

Expansion valve and evaporator

Compressor and evaporator

Compressor and condenser

Condenser and expansion valve

26. Superheating in a refrigeration cycle

Other factors decide C.O.P

Decreases C.O.P

C.O.P remains unaltered

Increases C.O.P

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

None of these

Mean radiant temperature

Effective temperature

Dew point temperature

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

Carbon dioxide

R-12

Sulphur dioxide

Ammonia

29. 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

30. The advantage of dry compression is that

It permits higher speeds to be used

It results in high volumetric and mechanical efficiency

It permits complete evaporation in the evaporator

All of the above

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

Same as

Lower than

Higher than

None of these

32. 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

1 kW

3 kW

2 kW

4 kW

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

After passing through the condenser

After passing through the expansion or throttle valve

Before passing through the condenser

Before entering the compressor

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

Room sensible heat load only

Both room sensible heat and latent heat loads

None of the above

Room latent heat load only

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

Superheated vapour

Dry saturated vapour

Saturated liquid

Wet vapour

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

Carbon dioxide

Ammonia

R-12

Sulphur dioxide

37. 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

Of adiabatic saturation of 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

38. The sub-cooling in a refrigeration cycle

Increases C.O.P.

None of these

Decreases C.O.P.

Does not alter C.O.P.

39. The specific humidity during dehumidification process

Increases

Remains constant

Decreases

None of these

40. 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)

(td₃ - td₂)/(td₃ - td₁)

(td₃ - td₁)/(td₃ - td₂)

(td₂ - td₃)/(td₃ - td₁)

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

Small

Equal

High

Anything

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

Direct

Compression

Indirect

Absorption

43. Ammonia absorption refrigeration cycle requires

Maximum work input

Zero work input

Very little work input

Nearly same work input as for vapour compression cycle

44. Moisture in Freon refrigeration system causes

Freezing automatic regulating valve

Corrosion of whole system

High power consumption

Ineffective refrigeration

45. 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 remain unaffected

Will be higher

Refrigeration & Air-Conditioning Practice Set-4

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