Refrigeration & Air-Conditioning Practice Set-4

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

Freon-22

Freon-12

NH3

CO2

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

Mixture of ice and water under equilibrium conditions

Solid and dry ice

Water at 0°C

Ice at 4°C

3. 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

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

More or less depending on ambient conditions

More

Same

Less

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

Heat of compression

All of the above

Enthalpy increase in compressor

Work done by compressor

6. 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

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

Increase

May increase or decrease depending on the type of refrigerant used

Remain unaffected

Decrease

8. The Freon group of refrigerants are

Inorganic refrigerants

Halocarbon refrigerants

Hydrocarbon refrigerants

Zoetrope refrigerants

9. 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 - td₂)/(td₃ - td₁)

(td₃ - td₁)/(td₂ - td₃)

(td₃ - td₁)/(td₃ - td₂)

(td₂ - td₃)/(td₃ - td₁)

10. Superheating in a refrigeration cycle

Decreases C.O.P

Other factors decide C.O.P

C.O.P remains unaltered

Increases C.O.P

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

All of these

Sulphur sticks

Halide torch

Soap and water

12. The specific humidity during dehumidification process

Remains constant

Increases

None of these

Decreases

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

Flooded

DX coil

None of these

Dry

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

Carbon dioxide

Sulphur dioxide

R-12

Ammonia

15. 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

16. 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

17. 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 - h2)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

(hA - h1)/ (h2 - h1)

(h2 - hA)/ (h1 - h2)

18. 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

Less than 2 kg

More than 10 kg

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

Before entering the compressor

After passing through the expansion or throttle valve

After passing through the condenser

Before passing through the condenser

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

Expansion valve and evaporator

Compressor and evaporator

Compressor and condenser

Condenser and expansion valve

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21. Air refrigeration operates on

Brayton cycle

Rankine’s cycle

Reversed Carnot cycle

Carnot cycle

22. 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)]

23. During sensible cooling,

Wet bulb temperature increases

Partial pressure of vapour remains constant

Specific humidity increases

Relative humidity remains constant

24. Ammonia absorption refrigeration cycle requires

Zero work input

Maximum work input

Very little work input

Nearly same work input as for vapour compression cycle

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

Evaporation of the refrigerant liquid

Compression of the refrigerant vapour

Condensation of the refrigerant vapour

Metering of the refrigerant liquid

26. Refrigeration in aeroplanes usually employs the following refrigerant

Air

Freon-22

CO2

Freon-11

27. Vapour compression refrigeration is somewhat like

Carnot cycle

None of the above

Reversed Carnot cycle

Rankine’s cycle

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

Superheated vapour

Saturated liquid

Wet vapour

Dry saturated vapour

29. Moisture in Freon refrigeration system causes

Corrosion of whole system

High power consumption

Freezing automatic regulating valve

Ineffective refrigeration

30. The advantage of dry compression is that

It permits higher speeds to be used

It results in high volumetric and mechanical efficiency

All of the above

It permits complete evaporation in the evaporator

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

Room sensible heat load only

None of the above

Both room sensible heat and latent heat loads

Room latent heat load only

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

Absolute

Specific

None of these

Relative

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

Effective temperature

None of these

Dew point temperature

Mean radiant temperature

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

Compression

Indirect

Absorption

Direct

35. The sub-cooling in a refrigeration cycle

Decreases C.O.P.

Increases C.O.P.

None of these

Does not alter C.O.P.

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

4 kW

1 kW

2 kW

3 kW

37. During cooling and dehumidification, dry bulb temperature

Increases

Decreases

Remains constant

None of these

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

Same as

Lower than

None of these

Higher than

39. Which of the following statement is correct?

The constant enthalpy lines are also constant wet bulb temperature lines

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

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

All of these

40. The superheating in a refrigeration cycle

Increases C.O.P.

None of these

Does not alter C.O.P.

Decreases C.O.P.

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41. The specific humidity during heating and humidification process.

None of these

Increases

Remains constant

Decreases

42. The relative coefficient of performance is

Actual COP × theoretical COP

None of these

Theoretical COP/actual COP

Actual COP/theoretical COP

43. Air conditioning means

Dehumidifying

Heating

All of these

Cooling

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

Equal

Anything

High

Small

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

R-12

Carbon dioxide

Sulphur dioxide

Ammonia

Refrigeration & Air-Conditioning Practice Set-4

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