Refrigeration & Air-Conditioning Practice Set-4

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1. Ammonia absorption refrigeration cycle requires

Very little work input

Maximum work input

Nearly same work input as for vapour compression cycle

Zero work input

2. The sub-cooling in a refrigeration cycle

None of these

Does not alter C.O.P.

Increases C.O.P.

Decreases C.O.P.

3. Air refrigeration operates on

Rankine’s cycle

Reversed Carnot cycle

Brayton cycle

Carnot cycle

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

NH3

Freon-22

Freon-12

CO2

5. 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

6. Air conditioning means

Heating

All of these

Cooling

Dehumidifying

7. Which of the following statement is correct?

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

All of these

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

The constant enthalpy lines are also constant wet bulb temperature lines

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

26°C DBT and 50% RH

20°C DBT and 60% RH

26°C DBT and 60% RH

20°C DBT and 50% RH

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

Superheated vapour

Dry saturated vapour

Wet vapour

Saturated liquid

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

All of these

Halide torch

Soap and water

Sulphur sticks

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

More

More or less depending on ambient conditions

Less

Same

12. The advantage of dry compression is that

It results in high volumetric and mechanical efficiency

It permits higher speeds to be used

It permits complete evaporation in the evaporator

All of the above

13. 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)

(hA - h2)/ (h1 - h2)

(h2 - hA)/ (h1 - h2)

(hA - h1)/ (h2 - h1)

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

Effective temperature

None of these

Dew point temperature

15. Vapour compression refrigeration is somewhat like

None of the above

Rankine’s cycle

Reversed Carnot cycle

Carnot cycle

16. Moisture in Freon refrigeration system causes

High power consumption

Freezing automatic regulating valve

Ineffective refrigeration

Corrosion of whole system

17. 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)

μ/[1 - (1 - μ) (Ps/Pb)]

None of these

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

18. Superheating in a refrigeration cycle

Decreases C.O.P

C.O.P remains unaltered

Increases C.O.P

Other factors decide C.O.P

19. During cooling and dehumidification, dry bulb temperature

None of these

Increases

Decreases

Remains constant

20. 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

Increase

Decrease

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21. During sensible cooling,

Partial pressure of vapour remains constant

Specific humidity increases

Relative humidity remains constant

Wet bulb temperature increases

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

Dry

Flooded

None of these

DX coil

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

Expansion valve and evaporator

Condenser and expansion valve

Compressor and condenser

Compressor and evaporator

24. The relative coefficient of performance is

Theoretical COP/actual COP

Actual COP × theoretical COP

None of these

Actual COP/theoretical COP

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

High

Equal

Small

Anything

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

0.2

5

6

1.2

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

Higher than

Lower than

Same as

None of these

28. The specific humidity during dehumidification process

Decreases

Increases

Remains constant

None of these

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

Compression of the refrigerant vapour

Evaporation of the refrigerant liquid

Condensation of the refrigerant vapour

Metering of the refrigerant liquid

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

Heat of compression

All of the above

Work done by compressor

Enthalpy increase in compressor

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31. Refrigeration in aeroplanes usually employs the following refrigerant

CO2

Air

Freon-11

Freon-22

32. The superheating in a refrigeration cycle

Does not alter C.O.P.

None of these

Decreases C.O.P.

Increases C.O.P.

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

Water at 0°C

Ice at 4°C

Mixture of ice and water under equilibrium conditions

Solid and dry ice

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

Direct

Indirect

Compression

Absorption

35. 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)

36. 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 be lower

Will be higher

Will remain unaffected

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

Sulphur dioxide

R-12

Ammonia

Carbon dioxide

38. 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 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

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

Relative

Specific

Absolute

None of these

40. 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

1 kW

4 kW

3 kW

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

Before passing through the condenser

Before entering the compressor

After passing through the expansion or throttle valve

After passing through the condenser

42. The specific humidity during heating and humidification process.

Remains constant

Decreases

None of these

Increases

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

Both room sensible heat and latent heat loads

Room latent heat load only

None of the above

Room sensible heat load only

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

Carbon dioxide

Sulphur dioxide

Ammonia

R-12

45. The Freon group of refrigerants are

Hydrocarbon refrigerants

Zoetrope refrigerants

Inorganic refrigerants

Halocarbon refrigerants

Refrigeration & Air-Conditioning Practice Set-4

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