Difference between revisions of "Relative Humidity"

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(Created page with "The question "What is Relative Humidity?" has multiple answers. The one that makes most sense is "How much water vapor can a solution hold above a salt solution compared to ...")
 
 
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We already calculate the activity of water and report it in the output. Thus if the water activity is 0.95 then we have a relative humidity of 95%.
 
We already calculate the activity of water and report it in the output. Thus if the water activity is 0.95 then we have a relative humidity of 95%.
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Please note, this definition only holds true if you have an aqueous liquid phase (liquid 1) present.  If your system is primarily hydrocarbon then this probably an overestimation.
  
 
[[user:jberthold | Author: Jim Berthold (OLI)]]
 
[[user:jberthold | Author: Jim Berthold (OLI)]]
 
[[Category: Thermodynamics]]
 
[[Category: Thermodynamics]]

Latest revision as of 16:58, 14 November 2019

The question "What is Relative Humidity?" has multiple answers.

The one that makes most sense is "How much water vapor can a solution hold above a salt solution compared to a pure water system at saturation pressure or temperature?"

This is really a function of the partial pressure of water (PH2O) above a salt solution compared to the pure component vapor pressure of water at the same temperature (T) and pressure (P).

So Relative Humidity is:

2016-11-08 12-05-25.png

Where PH2O(SALT) is the partial pressure of water above the salt solution and Vp(H2O) is the vapor pressure of water.

It turns out that this ratio is also a definition of the activity of water:

2016-11-08 12-08-34.png

We already calculate the activity of water and report it in the output. Thus if the water activity is 0.95 then we have a relative humidity of 95%.

Please note, this definition only holds true if you have an aqueous liquid phase (liquid 1) present. If your system is primarily hydrocarbon then this probably an overestimation.

Author: Jim Berthold (OLI)