Refrigeration & Air-Conditioning Practice Set-4

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

Compressor and condenser

Compressor and evaporator

Condenser and expansion valve

Expansion valve and evaporator

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

CO2

Freon-12

Freon-22

NH3

3. Air conditioning means

Heating

Dehumidifying

Cooling

All of these

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

All of these

Sulphur sticks

Soap and water

Halide torch

5. 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

6. Refrigeration in aeroplanes usually employs the following refrigerant

Air

Freon-11

Freon-22

CO2

7. Vapour compression refrigeration is somewhat like

Rankine’s cycle

Reversed Carnot cycle

Carnot cycle

None of the above

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

Indirect

Compression

Direct

Absorption

9. 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

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

Of adiabatic saturation of incoming stream

10. 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 - td₁)/(td₃ - td₂)

(td₂ - td₃)/(td₃ - td₁)

(td₃ - td₂)/(td₃ - td₁)

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11. The Freon group of refrigerants are

Hydrocarbon refrigerants

Halocarbon refrigerants

Zoetrope refrigerants

Inorganic refrigerants

12. 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

13. 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

3 kW

4 kW

2 kW

1 kW

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

None of these

Relative

Specific

Absolute

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

Wet vapour

Saturated liquid

Dry saturated vapour

Superheated vapour

16. 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

There is no such consideration

More than 10 kg

17. The specific humidity during dehumidification process

Decreases

Remains constant

Increases

None of these

18. Ammonia absorption refrigeration cycle requires

Maximum work input

Nearly same work input as for vapour compression cycle

Very little work input

Zero work input

19. 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

20. 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

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

Before passing through the condenser

After passing through the expansion or throttle valve

After passing through the condenser

Before entering the compressor

22. Moisture in Freon refrigeration system causes

High power consumption

Ineffective refrigeration

Corrosion of whole system

Freezing automatic regulating valve

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

Anything

Small

High

Equal

24. 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

1.2

6

0.2

5

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

Decrease

May increase or decrease depending on the type of refrigerant used

Remain unaffected

Increase

26. The specific humidity during heating and humidification process.

Decreases

None of these

Increases

Remains constant

27. During sensible cooling,

Partial pressure of vapour remains constant

Relative humidity remains constant

Specific humidity increases

Wet bulb temperature increases

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

20°C DBT and 50% RH

26°C DBT and 60% RH

20°C DBT and 60% RH

26°C DBT and 50% RH

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

Same

Less

More or less depending on ambient conditions

More

30. The relative coefficient of performance is

Actual COP × theoretical COP

Actual COP/theoretical COP

None of these

Theoretical COP/actual COP

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

DX coil

None of these

Dry

Flooded

32. The sub-cooling in a refrigeration cycle

None of these

Does not alter C.O.P.

Increases C.O.P.

Decreases C.O.P.

33. The superheating in a refrigeration cycle

Does not alter C.O.P.

Increases C.O.P.

None of these

Decreases C.O.P.

34. Air refrigeration operates on

Reversed Carnot cycle

Rankine’s cycle

Brayton cycle

Carnot cycle

35. During cooling and dehumidification, dry bulb temperature

None of these

Increases

Remains constant

Decreases

36. Superheating in a refrigeration cycle

Other factors decide C.O.P

Decreases C.O.P

C.O.P remains unaltered

Increases C.O.P

37. 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

38. 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)]

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

None of these

0.622 Pv / (Pb - Pv)

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)

(hA - h1)/ (h2 - h1)

(h1 - h2)/ (hA - h2)

(hA - h2)/ (h1 - h2)

(h2 - hA)/ (h1 - h2)

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

R-12

Ammonia

Sulphur dioxide

Carbon dioxide

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

None of these

Higher than

Lower than

Same as

42. Which of the following statement is correct?

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

All of these

The constant enthalpy lines are also constant wet bulb temperature lines

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

43. 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

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

Will be lower

44. 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 latent heat load only

Room sensible heat load only

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

R-12

Carbon dioxide

Ammonia

Sulphur dioxide

Refrigeration & Air-Conditioning Practice Set-4

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