Engineering ToolBox - Resources, Tools and Basic Information for Engineering and Design of Technical Applications!

Moist Air - Water Vapor and Saturation Pressure

Saturation pressure of water vapor in moist air vs. temperature.

Water vapor is almost always present in the surrounding air.

Note! - the equations below is for pure water vapor - not moist 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 - 7235 / T) / T 8.2 (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

p w = partial pressure water vapor (Pa, N/m2)

ρ w = density water vapor (kg/m3 )

T = absolute dry bulb temperature (K)

Saturation pressure and density of water vapor for common temperatures

Water vapor - temperature saturation pressure diagram

Water vapor - temperature saturation pressure diagram

Moist Air - Saturation Pressure and Density vs. Temperature
TemperatureSaturation PressureDensity
(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 - Saturation Pressure Water Vapor

The Saturation pressure of water vapor in moist air at dry bulb temperature 25 oC can be calculated:

First, convertion from °C to K:

( 25 °C) + 273 = 298 (K)

Then Eq. (1) is used:

pws = e (77.3450 + 0.0057 (298 K) - 7235 / (298 K) ) / 298 [K] 8.2

= 3130 (Pa)

Related Topics

  • Air Psychrometrics

    Moist and humid air calculations. Psychrometric charts and Mollier diagrams. Air-condition systems temperatures, absolute and relative humidities and moisture content in air.

Related Documents

Search

Search is the most efficient way to navigate the Engineering ToolBox.

Engineering ToolBox - SketchUp Extension - Online 3D modeling!

3D Engineering ToolBox Extension to SketchUp - add parametric components to your SketchUp model

Add standard and customized parametric components - like flange beams, lumbers, piping, stairs and more - to your Sketchup model with the Engineering ToolBox - SketchUp Extension - enabled for use with older versions of the amazing SketchUp Make and the newer "up to date" SketchUp Pro . Add the Engineering ToolBox extension to your SketchUp Make/Pro from the Extension Warehouse !

Translate this Page

Translate this page to Your Own Language .

About the Engineering ToolBox!

Privacy Policy

We don't collect information from our users. More about

We use a third-party to provide monetization technologies for our site. You can review their privacy and cookie policy here.

You can change your privacy settings by clicking the following button: .

Citation

This page can be cited as

  • The Engineering ToolBox (2004). Moist Air - Water Vapor and Saturation Pressure. [online] Available at: https://www.engineeringtoolbox.com/water-vapor-saturation-pressure-air-d_689.html [Accessed Day Month Year].

Modify the access date according your visit.

3D Engineering ToolBox - draw and model technical applications! 2D Engineering ToolBox - create and share online diagram drawing templates! Engineering ToolBox Apps - mobile online and offline engineering applications!

Unit Converter


















































11.25.10

.