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HYGROSCOPIC SWELLING

Posted Dec 22, 2016, 9:30 p.m. EST Version 5.0, Version 5.1, Version 5.2, Version 5.2a 4 Replies

Dickens Agumba
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Hi. Please help me out.

In hygroscopic modelling, the moisture concentration is given in mole/m^3.

In case I have a relative humidity of 40% at a temperature of 25 degrees Celsius, how do I convert this into mole/m^3.

Thank you.

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4 Replies Last Post Dec 26, 2016, 4:56 a.m. EST
Ross Wakelin
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Posted: 7 years ago Dec 23, 2016, 6:44 a.m. EST
If I understood your question correctly you want to express the relative humidty of the air in mol/m^3?. I would suggest you look at a "Psychrometric chart", eg en.wikipedia.org/wiki/Psychrometrics#/media/File:PsychrometricChart.SeaLevel.SI.svg
You then find where the 40% relative humidity intersects with the 25 deg C temperature and read off the humidity ratio which looks to be about 0,008 g water per g dry air (you can interpolate more accurately by measuring with a ruler).
Then you convert g water to mole and g air to m^3 air.
cheers
If I understood your question correctly you want to express the relative humidty of the air in mol/m^3?. I would suggest you look at a "Psychrometric chart", eg https://en.wikipedia.org/wiki/Psychrometrics#/media/File:PsychrometricChart.SeaLevel.SI.svg You then find where the 40% relative humidity intersects with the 25 deg C temperature and read off the humidity ratio which looks to be about 0,008 g water per g dry air (you can interpolate more accurately by measuring with a ruler). Then you convert g water to mole and g air to m^3 air. cheers
Dickens Agumba
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Posted: 7 years ago Dec 23, 2016, 8:59 a.m. EST
Wow! Thank you very much.

I got it pretty well.

Thanks once again for making me proceed with my work.
Wow! Thank you very much. I got it pretty well. Thanks once again for making me proceed with my work.
Henrik Sönnerlind COMSOL Employee

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Posted: 7 years ago Dec 23, 2016, 9:32 a.m. EST
By the way, you can also select to give the input in terms of mass concentration.

Either way, the humidity in in the surrounding air serves as a boundary condition for the moisture concentration in the solid you will analyze. It is not trivial how to transform the values in the surrounding air to values inside the solid.

The discussion in the documentation for this example:

www.comsol.com/model/mems-pressure-sensor-drift-due-to-hygroscopic-swelling-21021

will probably be of interest.

Regards,
Henrik
By the way, you can also select to give the input in terms of mass concentration. Either way, the humidity in in the surrounding air serves as a boundary condition for the moisture concentration in the solid you will analyze. It is not trivial how to transform the values in the surrounding air to values inside the solid. The discussion in the documentation for this example: https://www.comsol.com/model/mems-pressure-sensor-drift-due-to-hygroscopic-swelling-21021 will probably be of interest. Regards, Henrik
Dickens Agumba
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Posted: 7 years ago Dec 26, 2016, 4:56 a.m. EST
Thanks a lot sir. I appreciate your support.

Still facing some challenges though.

This property, CHS (Coefficient of Hygroscopic Swelling), I can't find a value for Polypyrrole.

I've worked on a variety of polymers with properties close to polypyrrole but the CHS varies a lot.

Any clue may help me. Thank you.
Thanks a lot sir. I appreciate your support. Still facing some challenges though. This property, CHS (Coefficient of Hygroscopic Swelling), I can't find a value for Polypyrrole. I've worked on a variety of polymers with properties close to polypyrrole but the CHS varies a lot. Any clue may help me. Thank you.

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