Refrigeration & Air-Conditioning Practice Set-4

June 7, 2021

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1. The Freon group of refrigerants are

Hydrocarbon refrigerants

Halocarbon refrigerants

Inorganic refrigerants

Zoetrope refrigerants

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

Water at 0°C

Ice at 4°C

Solid and dry ice

Mixture of ice and water under equilibrium conditions

3. Air refrigeration operates on

Brayton cycle

Reversed Carnot cycle

Rankine’s cycle

Carnot cycle

4. 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

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

Same as

Lower than

None of these

Higher than

6. 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)

(h1 - h2)/ (hA - h2)

(hA - h2)/ (h1 - h2)

(hA - h1)/ (h2 - h1)

(h2 - hA)/ (h1 - h2)

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

3 kW

2 kW

8. Refrigeration in aeroplanes usually employs the following refrigerant

Freon-22

Air

CO2

Freon-11

9. The sub-cooling in a refrigeration cycle

Does not alter C.O.P.

Increases C.O.P.

None of these

Decreases C.O.P.

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

CO2

Freon-12

Freon-22

NH3

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11. During cooling and dehumidification, dry bulb temperature

Remains constant

None of these

Decreases

Increases

12. Superheating in a refrigeration cycle

C.O.P remains unaltered

Other factors decide C.O.P

Increases C.O.P

Decreases C.O.P

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

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

Of adiabatic saturation of incoming stream

14. Vapour compression refrigeration is somewhat like

None of the above

Carnot cycle

Reversed Carnot cycle

Rankine’s cycle

15. 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 - td₂)/(td₃ - td₁)

(td₂ - td₃)/(td₃ - td₁)

(td₃ - td₁)/(td₃ - td₂)

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

None of these

Absolute

Specific

Relative

17. The relative coefficient of performance is

Theoretical COP/actual COP

Actual COP/theoretical COP

None of these

Actual COP × theoretical COP

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 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

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

Same

More or less depending on ambient conditions

Less

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

Enthalpy increase in compressor

All of the above

Heat of compression

Work done by compressor

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

Increase

Remain unaffected

May increase or decrease depending on the type of refrigerant used

Decrease

23. Air conditioning means

Dehumidifying

Cooling

Heating

All of these

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

Sulphur dioxide

Carbon dioxide

Ammonia

R-12

25. The specific humidity during dehumidification process

Decreases

None of these

Remains constant

Increases

26. 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

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

All of these

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

Evaporation of the refrigerant liquid

Metering of the refrigerant liquid

Condensation of the refrigerant vapour

Compression of the refrigerant vapour

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

Dry

Flooded

None of these

DX coil

29. The superheating in a refrigeration cycle

None of these

Does not alter C.O.P.

Decreases C.O.P.

Increases C.O.P.

30. 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

0.2

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31. The specific humidity during heating and humidification process.

Increases

Remains constant

None of these

Decreases

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

Ammonia

Carbon dioxide

Sulphur dioxide

R-12

33. During sensible cooling,

Specific humidity increases

Wet bulb temperature increases

Relative humidity remains constant

Partial pressure of vapour remains constant

34. 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

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

Will be lower

Will remain unaffected

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

Mean radiant temperature

None of these

Effective temperature

Dew point temperature

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

Halide torch

Sulphur sticks

All of these

Soap and water

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

Wet vapour

Dry saturated vapour

Saturated liquid

Superheated vapour

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

Indirect

Compression

Absorption

Direct

39. Moisture in Freon refrigeration system causes

Freezing automatic regulating valve

High power consumption

Ineffective refrigeration

Corrosion of whole system

40. 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

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41. 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

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

Condenser and expansion valve

Expansion valve and evaporator

Compressor and evaporator

Compressor and condenser

43. 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

There is no such consideration

More than or equal to 3.65 kg

44. 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)]

None of these

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

0.622 Pv / (Pb - Pv)

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

Small

Anything

High

Equal

Refrigeration & Air-Conditioning Practice Set-4

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