Refrigeration & Air-Conditioning Practice Set-4

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

Lower than

None of these

Same as

Higher than

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

R-12

Ammonia

Carbon dioxide

Sulphur dioxide

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

R-12

Sulphur dioxide

Ammonia

Carbon dioxide

4. 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

5. The Freon group of refrigerants are

Inorganic refrigerants

Hydrocarbon refrigerants

Zoetrope refrigerants

Halocarbon refrigerants

6. Moisture in Freon refrigeration system causes

Ineffective refrigeration

Freezing automatic regulating valve

High power consumption

Corrosion of whole system

7. Ammonia absorption refrigeration cycle requires

Maximum work input

Very little work input

Zero work input

Nearly same work input as for vapour compression cycle

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

None of these

Absolute

Specific

Relative

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

Direct

Compression

Absorption

Indirect

10. Air refrigeration operates on

Carnot cycle

Brayton cycle

Rankine’s cycle

Reversed Carnot cycle

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11. Vapour compression refrigeration is somewhat like

Carnot cycle

Reversed Carnot cycle

None of the above

Rankine’s cycle

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

There is no such consideration

More than or equal to 3.65 kg

More than 10 kg

Less than 2 kg

13. 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)

μ/[1 - (1 - μ) (Ps/Pb)]

0.622 Pv / (Pb - Pv)

None of these

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

14. 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

Effective temperature

None of these

Mean radiant temperature

15. The advantage of dry compression is that

It permits higher speeds to be used

All of the above

It permits complete evaporation in the evaporator

It results in high volumetric and mechanical efficiency

16. The sub-cooling in a refrigeration cycle

Increases C.O.P.

Decreases C.O.P.

None of these

Does not alter C.O.P.

17. The relative coefficient of performance is

Theoretical COP/actual COP

None of these

Actual COP × theoretical COP

Actual COP/theoretical COP

18. Which of the following statement is correct?

The constant enthalpy lines are also constant wet bulb temperature lines

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

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

CO2

Freon-22

NH3

Freon-12

20. 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)/(td₃ - td₂)

(td₃ - td₁)/(td₂ - td₃)

(td₃ - td₂)/(td₃ - td₁)

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

Both room sensible heat and latent heat loads

Room sensible heat load only

Room latent heat load only

None of the above

22. During cooling and dehumidification, dry bulb temperature

Increases

Decreases

Remains constant

None of these

23. The superheating in a refrigeration cycle

Increases C.O.P.

Decreases C.O.P.

Does not alter C.O.P.

None of these

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

After passing through the expansion or throttle valve

Before passing through the condenser

After passing through the condenser

Before entering the compressor

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

Small

Equal

Anything

High

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

20°C DBT and 50% RH

26°C DBT and 50% RH

20°C DBT and 60% RH

26°C DBT and 60% RH

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

Condensation of the refrigerant vapour

Evaporation of the refrigerant liquid

Metering of the refrigerant liquid

Compression of the refrigerant vapour

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

Flooded

DX coil

Dry

None of these

29. 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

Will remain unaffected

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

30. During sensible cooling,

Wet bulb temperature increases

Specific humidity increases

Relative humidity remains constant

Partial pressure of vapour remains constant

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31. Superheating in a refrigeration cycle

Decreases C.O.P

Other factors decide C.O.P

Increases C.O.P

C.O.P remains unaltered

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

Decrease

Increase

Remain unaffected

May increase or decrease depending on the type of refrigerant used

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

Compressor and condenser

Compressor and evaporator

Expansion valve and evaporator

Condenser and expansion valve

34. The specific humidity during dehumidification process

Decreases

Increases

Remains constant

None of these

35. Air conditioning means

Heating

Cooling

All of these

Dehumidifying

36. 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

2 kW

4 kW

3 kW

37. 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

0.2

6

1.2

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

All of the above

Work done by compressor

Enthalpy increase in compressor

Heat of compression

39. 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)

(h2 - hA)/ (h1 - h2)

(hA - h1)/ (h2 - h1)

(hA - h2)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

40. The specific humidity during heating and humidification process.

Increases

Decreases

None of these

Remains constant

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

Dry saturated vapour

Wet vapour

Superheated vapour

Saturated liquid

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

Sulphur sticks

Soap and water

Halide torch

All of these

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

Ice at 4°C

Water at 0°C

Solid and dry ice

Mixture of ice and water under equilibrium conditions

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

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

Of adiabatic saturation of incoming stream

Which lies between the dry bulb and wet bulb temperatures of the incoming stream

45. Refrigeration in aeroplanes usually employs the following refrigerant

Air

CO2

Freon-22

Freon-11

Refrigeration & Air-Conditioning Practice Set-4

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