Refrigeration & Air-Conditioning Practice Set-4

June 7, 2021

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1. The advantage of dry compression is that

It results in high volumetric and mechanical efficiency

All of the above

It permits complete evaporation in the evaporator

It permits higher speeds to be used

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

R-12

Ammonia

Carbon dioxide

Sulphur dioxide

3. Air refrigeration operates on

Carnot cycle

Brayton cycle

Reversed Carnot cycle

Rankine’s cycle

4. 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

1 kW

3 kW

2 kW

5. The superheating in a refrigeration cycle

None of these

Does not alter C.O.P.

Decreases C.O.P.

Increases C.O.P.

6. Superheating in a refrigeration cycle

Other factors decide C.O.P

Decreases C.O.P

Increases C.O.P

C.O.P remains unaltered

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

Small

Equal

High

Anything

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

Lower than

Higher than

Same as

None of these

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

Compressor and evaporator

Compressor and condenser

Condenser and expansion valve

Expansion valve and evaporator

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

More than or equal to 3.65 kg

Less than 2 kg

More than 10 kg

There is no such consideration

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11. The specific humidity during dehumidification process

Increases

Decreases

None of these

Remains constant

12. Air conditioning means

Cooling

Heating

Dehumidifying

All of these

13. 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

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

26°C DBT and 60% RH

20°C DBT and 60% RH

20°C DBT and 50% RH

26°C DBT and 50% RH

15. Moisture in Freon refrigeration system causes

Corrosion of whole system

Freezing automatic regulating valve

Ineffective refrigeration

High power consumption

16. Vapour compression refrigeration is somewhat like

None of the above

Rankine’s cycle

Reversed Carnot cycle

Carnot cycle

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

Flooded

Dry

None of these

DX coil

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

More or less depending on ambient conditions

Same

Less

19. 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

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

Absorption

Direct

Indirect

Compression

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21. During cooling and dehumidification, dry bulb temperature

Increases

Remains constant

Decreases

None of these

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

Both room sensible heat and latent heat loads

None of the above

Room sensible heat load only

Room latent heat load only

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

Ice at 4°C

Mixture of ice and water under equilibrium conditions

Solid and dry ice

Water at 0°C

24. The relative coefficient of performance is

Theoretical COP/actual COP

None of these

Actual COP × theoretical COP

Actual COP/theoretical COP

25. During sensible cooling,

Relative humidity remains constant

Specific humidity increases

Wet bulb temperature increases

Partial pressure of vapour remains constant

26. The Freon group of refrigerants are

Hydrocarbon refrigerants

Inorganic refrigerants

Zoetrope refrigerants

Halocarbon refrigerants

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

Dry saturated vapour

Superheated vapour

Wet vapour

Saturated liquid

28. Which of the following statement is correct?

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

The constant enthalpy lines are also constant wet bulb temperature lines

All of these

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

29. 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

μ/[1 - (1 - μ) (Ps/Pb)]

0.622 Pv / (Pb - Pv)

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

30. Ammonia absorption refrigeration cycle requires

Nearly same work input as for vapour compression cycle

Zero work input

Very little work input

Maximum work input

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31. 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 condenser

After passing through the expansion or throttle valve

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

R-12

Ammonia

Sulphur dioxide

Carbon dioxide

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

Relative

None of these

Absolute

Specific

34. The sub-cooling in a refrigeration cycle

Increases C.O.P.

Decreases C.O.P.

None of these

Does not alter C.O.P.

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

Heat of compression

Work done by compressor

All of the above

Enthalpy increase in compressor

36. Refrigeration in aeroplanes usually employs the following refrigerant

Freon-11

CO2

Air

Freon-22

37. 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)

(h1 - h2)/ (hA - h2)

(h2 - hA)/ (h1 - h2)

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

Halide torch

Sulphur sticks

Soap and water

All of these

39. 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

40. 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

Dew point temperature

None of these

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41. 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)/(td₃ - td₂)

(td₂ - td₃)/(td₃ - td₁)

(td₃ - td₂)/(td₃ - td₁)

(td₃ - td₁)/(td₂ - td₃)

42. 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

43. The specific humidity during heating and humidification process.

Decreases

Remains constant

Increases

None of these

44. 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

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

CO2

NH3

Freon-22

Freon-12

Refrigeration & Air-Conditioning Practice Set-4

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