Refrigeration & Air-Conditioning Practice Set-4

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1. Vapour compression refrigeration is somewhat like

None of the above

Carnot cycle

Rankine’s cycle

Reversed Carnot cycle

2. Air refrigeration operates on

Reversed Carnot cycle

Brayton cycle

Rankine’s cycle

Carnot cycle

3. 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

4. The Freon group of refrigerants are

Inorganic refrigerants

Hydrocarbon refrigerants

Zoetrope refrigerants

Halocarbon refrigerants

5. 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)/(td₂ - td₃)

(td₃ - td₁)/(td₃ - td₂)

(td₃ - td₂)/(td₃ - td₁)

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

DX coil

None of these

Dry

Flooded

7. 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

8. 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

More than 10 kg

There is no such consideration

Less than 2 kg

9. Which of the following statement is correct?

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

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

All of these

The constant enthalpy lines are also constant wet bulb temperature lines

10. 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

Effective temperature

Mean radiant temperature

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

Small

Equal

High

Anything

12. The advantage of dry compression is that

It results in high volumetric and mechanical efficiency

It permits complete evaporation in the evaporator

It permits higher speeds to be used

All of the above

13. The specific humidity during dehumidification process

Increases

Remains constant

None of these

Decreases

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

Halide torch

All of these

Soap and water

Sulphur sticks

15. The sub-cooling in a refrigeration cycle

Does not alter C.O.P.

Decreases C.O.P.

None of these

Increases C.O.P.

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

Less

Same

More

More or less depending on ambient conditions

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

Mixture of ice and water under equilibrium conditions

Solid and dry ice

Ice at 4°C

Water at 0°C

18. 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)]

None of these

0.622 Pv / (Pb - Pv)

μ/[1 - (1 - μ) (Ps/Pb)]

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

Same as

None of these

Higher than

Lower than

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

None of these

Specific

Absolute

Relative

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

Dry saturated vapour

Superheated vapour

Wet vapour

Saturated liquid

22. 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 remain unaffected

Will be lower

Will be higher

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

Ammonia

R-12

Carbon dioxide

Sulphur dioxide

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

After passing through the condenser

After passing through the expansion or throttle valve

Before entering the compressor

Before passing through the condenser

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

Enthalpy increase in compressor

Heat of compression

Work done by compressor

All of the above

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

Absorption

Compression

Direct

Indirect

27. Superheating in a refrigeration cycle

Increases C.O.P

Other factors decide C.O.P

Decreases C.O.P

C.O.P remains unaltered

28. 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

0.2

1.2

29. The superheating in a refrigeration cycle

None of these

Increases C.O.P.

Does not alter C.O.P.

Decreases C.O.P.

30. The relative coefficient of performance is

Actual COP × theoretical COP

Theoretical COP/actual COP

Actual COP/theoretical COP

None of these

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

May increase or decrease depending on the type of refrigerant used

Decrease

Increase

Remain unaffected

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

Condenser and expansion valve

Compressor and evaporator

Compressor and condenser

Expansion valve and evaporator

33. During sensible cooling,

Specific humidity increases

Relative humidity remains constant

Partial pressure of vapour remains constant

Wet bulb temperature increases

34. Moisture in Freon refrigeration system causes

Freezing automatic regulating valve

Corrosion of whole system

Ineffective refrigeration

High power consumption

35. During cooling and dehumidification, dry bulb temperature

Decreases

None of these

Increases

Remains constant

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

Room latent heat load only

Room sensible heat load only

Both room sensible heat and latent heat loads

None of the above

37. The specific humidity during heating and humidification process.

Decreases

None of these

Remains constant

Increases

38. Refrigeration in aeroplanes usually employs the following refrigerant

Air

Freon-22

CO2

Freon-11

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

Evaporation of the refrigerant liquid

Condensation of the refrigerant vapour

Metering of the refrigerant liquid

Compression of the refrigerant vapour

40. Ammonia absorption refrigeration cycle requires

Very little work input

Zero work input

Nearly same work input as for vapour compression cycle

Maximum work input

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

Freon-22

NH3

Freon-12

CO2

42. Air conditioning means

All of these

Dehumidifying

Heating

Cooling

43. 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 lies between the dry bulb and wet bulb temperatures of the incoming stream

Which is lower than the dew point temperature of the incoming stream

Of adiabatic saturation of incoming stream

44. 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)

(h2 - hA)/ (h1 - h2)

(hA - h1)/ (h2 - h1)

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

Ammonia

R-12

Carbon dioxide

Sulphur dioxide

Refrigeration & Air-Conditioning Practice Set-4

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