exceeding RH100%

[shinya]

In a result of my calculation, the RH exceeded 100%.
It was 100%~105%.

Is this calculation correct?
What does the part of over 100% mean?

Please give me some information.

[Thomas]

Hi shinya,

a relative humidity exceeding 100% means that the water content of the material exceeds free saturation.

Free saturation is the water content up to which a material can absorb liquid water to which it is exposed (rain, for example). Since during the absorption of liquid water air pockets will be trapped in the pores, free saturation is less than maximum saturation where the complete pore volume is filled.

Water contents between free and maximum saturation can be reached if condensation occurs (because condensation starts at the tiny ends of the pores and pushes all air out of the pores). While for humidities below 100% there is a unique mathematical relationship (the "moisture storage function") between relative humidity and moisture content, no unique relationship exists above 100%.

However, WUFI needs such a relationship in order to mathematically solve the moisture transport equations. Therefore WUFI artificially assigns relative humidities above 100% to the moisture contents between free saturation and maximum saturation. In all places where this occurs in your calculation you should also see a water content above free saturation.

These relative humidities above 100% have no real physical meaning and should be treated as being 100% (this is what you would measure in an experiment). WUFI only uses them for mathematical consistency in its equations. Maybe we should limit all relative humidities in the output of the program to 100% in order not to confuse the user...

Regards,
Thomas

[Alberto Morales]

hi Thomas,

is this still valid (see message above)?

Thanks

[Thomas]

Hi Alberto,

the internal handling of moisture contents exceeding free saturation is still the same. In the one-dimensional WUFI-Pro the relative humidities in the output data are automatically limited to 100 %. I'm not really sure right now about WUFI-2D. I think it's limited there now as well, but I'm not 101 % ( ) sure. Should you see humidities exceeding 100 % in the output, please treat them as 100 %.

Kind regards,
Thomas

[Alberto Morales]

Thanks

[katinkar]

Hi,

Does this imply that one could evaluate an RH level<100% (water content above free saturation) as a possible sign of condensation happening?

Kind regards,
Katinka

[Christian Bludau]

Hi Katinka,

Does this imply that one could evaluate an RH level<100% (water content above free saturation) as a possible sign of condensation happening?

At 100% RH all pores are filled with water, so that point out for dew water at a position. As smaller pores may be filled with water below 100% RH, it depends on the the size distribution of the pores, how many are filled up below 100%

Dew water is more a measure from the steady state calculations. From the transient view the water content is rising at one position depending on the moisture storage function of a material and over about 97% (depending on the material) there is liquid water in the pores or around the fibers which can be counted as a kind of dew water, but does not necessarily drip off.

Christian