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Author: [[User:Hschwarz|Hans-Jürgen Schwarz]]  
moved to the content page[[User:Hschwarz|Hschwarz]] 18:10, 3 October 2012 (CEST)
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Back to [[Air humidity Measurement|Air humidity measurement]]
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== Abstract  ==
 
== Dalton's Law ==
 
The total pressure of a gas mixture is composed of the sum of the partial pressures of the constituents.
In simplified terms: the air consists of dry air and water vapor
 
<math>P  = P_w + P_dry</math>
 
wherein P<sub>w</sub> constitutes the partial pressure generated by water vapor and P<sub>dry</sub> represents the sum of all partial pressures of all the other gases.<br>
 
 
{|cellspacing="0" cellpadding = "10" align="center" style="border-style:solid; border-color:black; border-width:1px;"
|bgcolor="#ffff99" align="center"|The total pressure of a mixture of ideal gases is equal to the sum of partial pressures of the individual gases in the mixture.
|}<br>
 
 
 
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==Water vapor in the air==
In a gas mixture (volume V, temperature T), each component gas has a partial pressure, pi, which it would have, if all the other gases were not present<ref>http://de.wikipedia.org/w/index.php?title=Partialdruck&oldid=77071731 gelesen 29.07.2010</ref>.
 
 
<!--[[Datei:Wasserdampfpartialdruck.JPG|thumb|400px|right|'''Abbildung 1''' - Wasserdampfpartialdruck]]-->
 
For the relationship between pi, V and T, the following equation applies:
 
<math>p*v = n*R*T</math>
 
The total pressure is the sum of all partial pressures.
Water vapor partial pressure is at
 
{|border="0" cellspacing="2" width="30%"
|22 ºC and 100 %rF
|= 2645 Pa
 
|-
|22 ºC and 67 %rF
|= 1772 Pa
 
|}
 
(1 Pa = 1N/m² = 0.01 mbar)
 
The atmospheric pressure in Hannover, for example, fluctuates between 964 hPa and 1042 hPa.
 
The partial pressure of water vapor at a given temperature cannot exceed certain limits, i.e. saturation. When the saturation pressure p<sub>s</sub> is increased by additional water supply (humidification), the partial pressure stays the same, but the excess water vapor precipitates in the form of liquid water. This is called condensate.
There is no simple physical relation between temperature and saturation pressure, which is why the relationship is expressed in graphical or in table form.
 
The saturation pressure increases considerably, when temperature rises. For instance, at 0 ºC it is 611 Pa and at 20 ºC already 2338 Pa.
 
== WebLinks ==
 
The physics of the museum environment by Tim Padfield: http://www.natmus.dk/cons/tp/index.htm
 
<references />
 
== Literature ==
 
<!--<biblist/> -->
 
[[Category:Climatic measurements]] [[Category:R-HSchwarz]] [[Category:R-SLaue]] [[Category:Schwarz,Hans-Jürgen]] [[Category:Review]]


[[User:SLeithaeuser|SLeithaeuser]] 12:08, 3 October 2012 (CEST)
[[User:SLeithaeuser|SLeithaeuser]] 12:08, 3 October 2012 (CEST)

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