Discussion Forum

Posted: 1 decade ago Feb 4, 2012, 5:09 a.m. EST

[QUOTE] I have water vapor + air that are diffusing in a porous media from one side of porous media, and from other side of this porous media I have liquid water entering in. There is also a phase change for water which effects water concentrations (in gas and liquid phases) in porous media. so my question is if I specify my geometry ( porous media) as a domain for water vapor for example. so how comsol can build a connection between water vapor and water liquid. or how can I determine the temperature of air, when I have only added the water vapor ( steam) as material for geometry? shouldn't be an option for contributing these materials instead of overriding (because when you add another material to same geometry it overrides the previous one) ? Because comsol only allows us to add one material for porous media, but I need to apply heat transfer on all of these materials in porous media. so what should I do ? I am new to comsol, and I am testing comsol's abilities. so please tell me whether you can have a geometry with few materials applied to all of that geometry and not parts of it ( like multi-component flow inside a pipe) ? Thank you very much [/QUOTE] THis cannot be currently modelled in any softwares i know .. and i have requested for a similar problem my problem is as follows: "porous solid with air gap is being heated aand undergoes phase change. the air escapes while the glass melts and compacts .. " when you have too many non lineraity and complexities like .. porous medium, phase change, convection contribution due to phase change ... no softwares can model this ... So better write equations and start solving them as ODEs in COMSOL or better approximate the situation and get some solution as approximate anwers and find the deviations :)

Posted: 1 decade ago Feb 4, 2012, 12:32 p.m. EST

Hi, Contrary to Santhosh, I think that there is hope for your problem. As a 1st approach (which is already a big challenge), I would try with these interfaces (CFD and Chemical reaction eng. modules): - Species transport in variably saturated media (2 species: water and vapor) - Two-phase Darcy's law You definitely better go isothermal first. You can include all kinds of stuff in the species equations: diffusion, dispersion, reaction, adsorption. It is certainly possible to model water evaporation/condensation with reaction terms function of temperature. But regarding the temperature, I don't think that it's possible to solve multiple temperatures (water T, vapor T, matrix T). The heat transfer in porous media assumes a local thermodynamic equilibrium. But is it possible to use 3 nodes and adjust the source terms in order to obtain 3 temperatures: 2 heat transfer in fluids and 1 heat transfer in solid??? it's just an idea. Good luck

Posted: 1 decade ago Feb 5, 2012, 1:05 p.m. EST

[QUOTE] You definitely better go isothermal first. You can include all kinds of stuff in the species equations: diffusion, dispersion, reaction, adsorption. It is certainly possible to model water evaporation/condensation with reaction terms function of temperature. But regarding the temperature, I don't think that it's possible to solve multiple temperatures (water T, vapor T, matrix T). The heat transfer in porous media assumes a local thermodynamic equilibrium. But is it possible to use 3 nodes and adjust the source terms in order to obtain 3 temperatures: 2 heat transfer in fluids and 1 heat transfer in solid??? it's just an idea. [/QUOTE] First Thank you for your replies now, I think it is possible too, just needs little programming. I was thinking about same thing as Francois, using 3 nodes for heat transfer and connecting them to diffusion and convection with little Programming. I hope it works. Comsol is really great software but I think in the beginning when they started to design this software their goal wasn't to design it for chemical engineers like me and they added it's chemical engineering modules later. So it needs little changes to satisfy a chemical engineer's needs, and hopefully they'll implements those changes.

Posted: 1 decade ago Feb 18, 2012, 2:13 a.m. EST

Hi Kevin, I am new in COMSOL and want to implement my own PDEs in COMSOL by using the coefficient form PDE of Maths module in version 4.0a. I will heat a mixture of oil and water by using electromagnetic waves and while heating I will have to take care of the fluid flow as well. In the mean time, temperature of water will rise and it will start converting to vapours (steam) but I do not know how to model this phase change of water in COMSOL? Can you please help me in doing so i.e. how to change the phase of water with the rise of temperature? I read your post but could not understand what type of code you have written and how to insert this code in COMSOL? Many thanks in advance for any of your help.