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https://www.mesubjects.net/wp-admin/post.php?post=4194&action=edit MCQ non-conventional refrigeration
Psychrometry is the study of the
properties of moist air (dry air + water
vapor). It includes the study of various
temperatures, humidity and Psychrometric
Mixture of gases (mainly oxygen and nitrogen) which does not contain water vapor.
2. Wet air
Wet air or moist air is a mixture of dry air and water vapor.
3. Saturated air
Saturated air is one which contains maximum water vapors at a particular temperature.
For saturated air,
Dry bulb temperature= wet bulb temperature= dew point temperatures
Relative humidity is 100 %.
4. Dry air temperature
Temperature of dry air is the temperature of atmospheric air (moist air). A thermometer measures dry bulb temperature.
5. Wet bulb temperature
Temperature of fully saturated air. Wet bulb thermometer measures it. Sling Psychrometer has the wet bulb thermometer..
6. Sling Psychrometer
Sling psychrometer measures dry and wet bulb temperatures.
7. Dew point temperature
Dew point temperature is that temperature at which first condensation of water vapor takes place on cooling the moist air. Dry bulb temperature is greater than wet bulb temperature. Wet bulb temperature is greater than dew point temperature.
9. Specific humidity
Specific humidity (w) is the amount of water vapor per kg of dry air. Mathematically
w = 0.622 pwv/(pt–pwv)
10. Relative humidity
Relative humidity is at a particular temperature on volume basis.
mass of H2O vapor in moist air/ mass of H2O vapor when saturated
Expressed as ‰ .
Its symbol is ‘Ф’.
Ф = pv/pvs
Where pv is pressure of water vapors. Read from steam tables at the dry bulb temperature.
pvs pressure of water vapors when saturated
Read from steam tables at the wet bulb temperature.
11. Degree of saturation
Degree of saturation is at a particular temperature.
It is on mass basis.
Its symbol is ‘ μ’.
μ = mass of H2O vapor/mass of H2O vapor when saturated
It has no units.
Example, its value is like 0.56
12. Enthalpy of moist air
Enthalpy of moist air = enthalpy of dry air + enthalpy of water vapor portion in 1 kg of dry air
Let w be the mass of water vapor in 1 kg of moist air. Mathematically
Enthalpy of moist air/kg of dry air, hma
hma = 1 cp dt + w [hg +cpv (tdb -tdp)]