Refrigeration & Air-Conditioning Practice Set-4

June 7, 2021

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1. The superheating in a refrigeration cycle

Increases C.O.P.

None of these

Does not alter C.O.P.

Decreases C.O.P.

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

Both room sensible heat and latent heat loads

Room latent heat load only

Room sensible heat load only

None of the above

3. 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

1.2

4. During sensible cooling,

Specific humidity increases

Relative humidity remains constant

Wet bulb temperature increases

Partial pressure of vapour remains constant

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

CO2

Freon-22

NH3

Freon-12

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

Decrease

Increase

May increase or decrease depending on the type of refrigerant used

Remain unaffected

7. 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 10 kg

More than or equal to 3.65 kg

Less than 2 kg

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

Absorption

Direct

Indirect

Compression

9. Moisture in Freon refrigeration system causes

Ineffective refrigeration

Freezing automatic regulating valve

Corrosion of whole system

High power consumption

10. The advantage of dry compression is that

It results in high volumetric and mechanical efficiency

It permits complete evaporation in the evaporator

All of the above

It permits higher speeds to be used

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11. 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)

(hA - h2)/ (h1 - h2)

(h2 - hA)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

12. In order to cool and dehumidify a stream of moist air, it must be passed over the coil at a temperature

Of adiabatic saturation of incoming stream

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

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

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

None of these

Relative

Absolute

Specific

14. The specific humidity during heating and humidification process.

Increases

Decreases

Remains constant

None of these

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

20°C DBT and 60% RH

26°C DBT and 50% RH

20°C DBT and 50% RH

26°C DBT and 60% RH

16. 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)

(td₂ - td₃)/(td₃ - td₁)

(td₃ - td₁)/(td₂ - td₃)

(td₃ - td₂)/(td₃ - td₁)

17. Air conditioning means

All of these

Heating

Dehumidifying

Cooling

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

DX coil

Dry

None of these

Flooded

19. The relative coefficient of performance is

None of these

Actual COP × theoretical COP

Actual COP/theoretical COP

Theoretical COP/actual COP

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

Compression of the refrigerant vapour

Condensation of the refrigerant vapour

Metering of the refrigerant liquid

Evaporation of the refrigerant liquid

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21. The Freon group of refrigerants are

Hydrocarbon refrigerants

Halocarbon refrigerants

Inorganic refrigerants

Zoetrope refrigerants

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

Sulphur dioxide

Carbon dioxide

R-12

Ammonia

23. 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

2 kW

1 kW

3 kW

24. 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

μ/[1 - (1 - μ) (Ps/Pb)]

0.622 Pv / (Pb - Pv)

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

Water at 0°C

Mixture of ice and water under equilibrium conditions

Ice at 4°C

Solid and dry ice

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

Wet vapour

Superheated vapour

Dry saturated vapour

Saturated liquid

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

After passing through the condenser

Before passing through the condenser

Before entering the compressor

After passing through the expansion or throttle valve

28. The sub-cooling in a refrigeration cycle

Decreases C.O.P.

Does not alter C.O.P.

None of these

Increases C.O.P.

29. 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

All of these

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

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

Compressor and evaporator

Compressor and condenser

Condenser and expansion valve

Expansion valve and evaporator

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31. 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

32. 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 be lower

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

Will remain unaffected

33. The specific humidity during dehumidification process

Decreases

Increases

Remains constant

None of these

34. During cooling and dehumidification, dry bulb temperature

Increases

Decreases

Remains constant

None of these

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

Enthalpy increase in compressor

Work done by compressor

All of the above

Heat of compression

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

Lower than

Higher than

None of these

Same as

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

Ammonia

Sulphur dioxide

R-12

Carbon dioxide

38. Refrigeration in aeroplanes usually employs the following refrigerant

CO2

Freon-22

Air

Freon-11

39. Vapour compression refrigeration is somewhat like

Carnot cycle

None of the above

Rankine’s cycle

Reversed Carnot cycle

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

Equal

Anything

Small

High

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41. Superheating in a refrigeration cycle

C.O.P remains unaltered

Increases C.O.P

Decreases C.O.P

Other factors decide C.O.P

42. 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

Mean radiant temperature

None of these

Effective temperature

43. Air refrigeration operates on

Reversed Carnot cycle

Rankine’s cycle

Carnot cycle

Brayton cycle

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

Sulphur sticks

Soap and water

All of these

Halide torch

45. Ammonia absorption refrigeration cycle requires

Maximum work input

Very little work input

Nearly same work input as for vapour compression cycle

Zero work input

Refrigeration & Air-Conditioning Practice Set-4

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