Water Vapor and Saturation Pressure in Humid Air
The saturation pressure of water vapor in moist air varies with temperature
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Water vapor is almost always present in the surrounding air.
Saturation Pressure of Water Vapor
The maximum saturation pressure of the water vapor in moist air varies with the temperature of the air vapor mixture and can be expressed as:
pws = e(77.3450 + 0.0057 T - 7,235 / T) / T8.2 (1)
where
pws = water vapor saturation pressure (Pa)
e = the constant 2.718.......
T = dry bulb temperature of the moist air (K)
Density of Water Vapor
The density of water vapor can be expressed as:
ρw = 0.0022 pw / T (2)
where
pw = partial pressure water vapor (Pa, N/m2)
ρw = density water vapor (kg/m3)
T = absolute dry bulb temperature (K)
Saturation pressure and density of water vapor for common temperatures:
| Temperature | Saturation Pressure | Density | |||||
| (oC) | (oF) | (Pa) | (mmHg) | (psia) | (inHg) | (kg/m3) | 10-3 (lb/ft3) |
| 0 | 32 | 603 | 4.6 | 0.09 | 0.18 | 0.005 | 0.30 |
| 10 | 50 | 1212 | 9.2 | 0.18 | 0.36 | 0.009 | 0.59 |
| 20 | 68 | 2310 | 17.4 | 0.33 | 0.68 | 0.017 | 1.08 |
| 30 | 86 | 4195 | 31.7 | 0.61 | 1.24 | 0.030 | 1.90 |
| 40 | 104 | 7297 | 55.1 | 1.06 | 2.15 | 0.051 | 3.20 |
| 50 | 122 | 12210 | 92.2 | 1.8 | 3.60 | 0.083 | 5.19 |
| 60 | 140 | 19724 | 149 | 2.9 | 5.82 | 0.13 | 8.13 |
| 70 | 158 | 30866 | 233 | 4.5 | 9.11 | 0.20 | 12.3 |
| 80 | 176 | 46925 | 354 | 6.8 | 13.8 | 0.29 | 18.2 |
| 90 | 194 | 69485 | 525 | 10.1 | 20.5 | 0.42 | 26.3 |
| 100 | 212 | 100446 | 758 | 14.6 | 29.6 | 0.59 | 36.9 |
| 120 | 248 | 196849 | 1486 | 28.6 | 58.1 | 1.10 | 68.7 |
| 140 | 284 | 358137 | 2704 | 51.9 | 105.7 | 1.91 | 119 |
| 160 | 320 | 611728 | 4619 | 88.7 | 180.5 | 3.11 | 194 |
| 180 | 356 | 990022 | 7475 | 144 | 292.1 | 4.80 | 300 |
| 200 | 392 | 1529627 | 11549 | 222 | 451.2 | 7.11 | 444 |
- 1 lb/ft3 = 16.018 kg/m3
- 1 kg/m3 = 0.0624 lb/ft3
Example - The Saturation Pressure of Water Vapor
The Saturation pressure of water vapor in moist air at dry bulb temperature 25oC can be calculated as:
pws = e( 77.3450 + 0.0057 (273 + 25) - 7,235 / (273 + 25) ) / (273 + 25)8.2
= 3,130 Pa
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Related Topics
- Air Psychrometrics - The study of moist and humid air - air condition - psychrometric charts, Mollier diagrams, air temperature, absolute and relative humidity, moisture content and more .
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Related Documents
- Density of Dry Air, Water Vapor and Moist Humid Air - Calculate the density of dry air, water vapor or the mixture of air and water vapor - moist or humid air
- Drying Force of Air - The Drying Force of air may be expressed as the moisture holding capacity of the air and the evaporation capacity from a water surface to the air
- Heat Removed by Air - Heat removed with air - dry and wet bulb temperature
- Mole Fraction of Water Vapor in Moist Air - Mole fraction of water vapor expresses the ratio of water molecules - to air and water molecules
- Vapor Pressure - Saturation pressure - exerted by escaping molecules
- Vapor Pressure in Moist Air - Vapor pressures in moist air from dry and wet bulb temperatures
- Water Saturation Pressure - Water saturation pressure at temperatures ranging 0 - 100 oC and 32 - 700 oF - Imperial and SI Units
