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Note: This discussion is about an older version of the COMSOL Multiphysics® software. The information provided may be out of date.

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differential equations with few variables in Comsol 4.2

Posted 31.08.2012, 13:46 GMT-4 Version 4.2 4 Replies

Roman Shchupakivskyy
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Hi for all!
I'm trying to simulate the heat and mass transfer process in wood during drying.
I need to investigate the distribution of temperature T and moisture content U in the wood during the drying process in air.
I have a set of equations that describe this process:

pCq*dT/dt = grad[ (X1+X2)grad(T) + X3grad(U) ]
pCm*dU/dt = grad[ (X4)grad(U) + X5grad(T) ]

U = f(t) - moisture content
T = f(t) -temperature
t - time
X2,X3 = f(T,U)
X1,X4,X5 - coefficients


I tried to solve it with PDE, but I don`t understand how I can introduce second variable U into eguation?
How this can be implemented in Comsol 4.2?

p.s. I should be grateful for your help!
4 Replies Last Post 08.02.2013, 01:57 GMT-5
Zhangxian Deng
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Posted: 1 decade ago 31.08.2012, 13:51 GMT-4
Click the "Physics", I think the physics is "PDE" for you.

In the end, you can find "independent variables".

You can change the independent variable number to 2. The default is 1, so you can only add a single variable named "U".

Hope I solve your problem.

Dan
Click the "Physics", I think the physics is "PDE" for you. In the end, you can find "independent variables". You can change the independent variable number to 2. The default is 1, so you can only add a single variable named "U". Hope I solve your problem. Dan
Roman Shchupakivskyy
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Posted: 1 decade ago 31.08.2012, 15:33 GMT-4
Dan, thank you very much for reply, but, actually, I know how to do this.

The problem is next - when I open PDE general form (for example) I have in Subdomain Setting typical equation like this:
- [ ead2u/dt2 + dadu/dt + gradГ = F ],

or

in PDE coefficient form:
- [ ead2u/dt2 + da du/dt + grad(-c gradu – au + y)+ au + b gradu = f ].

And I don`t know how to change this equation to my type which I need: pCq*dT/dt = grad[(X1+X2)grad(T) + X3grad(U)]

Thanks for your help...
Dan, thank you very much for reply, but, actually, I know how to do this. The problem is next - when I open PDE general form (for example) I have in Subdomain Setting typical equation like this: - [ ead2u/dt2 + dadu/dt + gradГ = F ], or in PDE coefficient form: - [ ead2u/dt2 + da du/dt + grad(-c gradu – au + y)+ au + b gradu = f ]. And I don`t know how to change this equation to my type which I need: pCq*dT/dt = grad[(X1+X2)grad(T) + X3grad(U)] Thanks for your help...
Xiangmei Meng
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Posted: 1 decade ago 06.02.2013, 10:54 GMT-5
Did you find out how to solve these equations in Comsol??? Now I am doing the simulation about drying, and have the similar problem. If you already solved the problem, maybe you can give me some suggestions. Thanks!
Did you find out how to solve these equations in Comsol??? Now I am doing the simulation about drying, and have the similar problem. If you already solved the problem, maybe you can give me some suggestions. Thanks!
Roman Shchupakivskyy
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Posted: 1 decade ago 08.02.2013, 01:57 GMT-5
Hi! Actuarly I`ve solved this problem but not at all. The programm works, but still I have some questions, for example - non-lineair temperature increase during process, different types of boundary conditions, etc. I wil try to help you. Tell me what do you wish to know?
Hi! Actuarly I`ve solved this problem but not at all. The programm works, but still I have some questions, for example - non-lineair temperature increase during process, different types of boundary conditions, etc. I wil try to help you. Tell me what do you wish to know?

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