Refrigeration & Air-Conditioning Practice Set-4

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

Expansion valve and evaporator

Compressor and evaporator

Compressor and condenser

Condenser and expansion valve

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

Same as

Higher than

Lower than

None of these

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

Solid and dry ice

Mixture of ice and water under equilibrium conditions

Ice at 4°C

Water at 0°C

4. Air refrigeration operates on

Rankine’s cycle

Brayton cycle

Reversed Carnot cycle

Carnot cycle

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

Heat of compression

Enthalpy increase in compressor

All of the above

Work done by compressor

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

Specific

None of these

Absolute

Relative

7. The specific humidity during dehumidification process

Remains constant

Decreases

Increases

None of these

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

Ammonia

Sulphur dioxide

Carbon dioxide

R-12

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

20°C DBT and 60% RH

20°C DBT and 50% RH

26°C DBT and 50% RH

26°C DBT and 60% RH

10. 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)

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

0.622 Pv / (Pb - Pv)

None of these

μ/[1 - (1 - μ) (Ps/Pb)]

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11. Refrigeration in aeroplanes usually employs the following refrigerant

Air

Freon-11

CO2

Freon-22

12. Ammonia absorption refrigeration cycle requires

Zero work input

Maximum work input

Very little work input

Nearly same work input as for vapour compression cycle

13. 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)

(td₃ - td₁)/(td₂ - td₃)

(td₃ - td₂)/(td₃ - td₁)

(td₂ - td₃)/(td₃ - td₁)

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

Flooded

DX coil

None of these

Dry

15. The specific humidity during heating and humidification process.

Decreases

Remains constant

None of these

Increases

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

Equal

Small

Anything

High

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

Freon-12

Freon-22

CO2

NH3

18. 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)

(h2 - hA)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

(hA - h2)/ (h1 - h2)

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

Dry saturated vapour

Superheated vapour

Saturated liquid

Wet vapour

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

Before entering the compressor

Before passing through the condenser

After passing through the expansion or throttle valve

After passing through the condenser

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21. 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

None of these

Mean radiant temperature

Effective temperature

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

All of these

Sulphur sticks

Halide torch

Soap and water

23. During sensible cooling,

Specific humidity increases

Partial pressure of vapour remains constant

Relative humidity remains constant

Wet bulb temperature increases

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

Metering of the refrigerant liquid

Condensation of the refrigerant vapour

Compression of the refrigerant vapour

Evaporation of the refrigerant liquid

25. Superheating in a refrigeration cycle

C.O.P remains unaltered

Increases C.O.P

Other factors decide C.O.P

Decreases C.O.P

26. The Freon group of refrigerants are

Inorganic refrigerants

Halocarbon refrigerants

Hydrocarbon refrigerants

Zoetrope refrigerants

27. 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 dry bulb and wet bulb temperatures of the incoming stream

Of adiabatic saturation of incoming stream

Which lies between the wet bulb and dew point temperatures of the incoming stream

28. 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

3 kW

2 kW

4 kW

29. 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

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

Less

More or less depending on ambient conditions

Same

More

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31. During cooling and dehumidification, dry bulb temperature

Decreases

Increases

None of these

Remains constant

32. Moisture in Freon refrigeration system causes

Corrosion of whole system

Freezing automatic regulating valve

Ineffective refrigeration

High power consumption

33. 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

Decrease

Remain unaffected

34. Vapour compression refrigeration is somewhat like

None of the above

Reversed Carnot cycle

Rankine’s cycle

Carnot cycle

35. 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

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

All of these

36. 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

6

5

1.2

0.2

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

Direct

Compression

Indirect

Absorption

38. 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 remain unaffected

Will be higher

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

39. The sub-cooling in a refrigeration cycle

None of these

Decreases C.O.P.

Increases C.O.P.

Does not alter C.O.P.

40. The relative coefficient of performance is

Theoretical COP/actual COP

Actual COP × theoretical COP

Actual COP/theoretical COP

None of these

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

Room sensible heat load only

None of the above

Room latent heat load only

Both room sensible heat and latent heat loads

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

More than 10 kg

Less than 2 kg

More than or equal to 3.65 kg

There is no such consideration

43. The superheating in a refrigeration cycle

Increases C.O.P.

None of these

Decreases C.O.P.

Does not alter C.O.P.

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

Ammonia

R-12

Carbon dioxide

Sulphur dioxide

45. Air conditioning means

Heating

Dehumidifying

All of these

Cooling

Refrigeration & Air-Conditioning Practice Set-4

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