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Thread Subject:
Phase Transition (Freezing) in FEMLAB

Subject: Phase Transition (Freezing) in FEMLAB

From: Habakuk

Date: 1 Dec, 2005 07:42:50

Message: 1 of 4

Hi to everybody!
I´m a new Femlab user and I´ve following problem:
I want to simulate a tip which freezes biological tissue. For this i
use the Heat Transfer module (BioHeatEquation). Now i have the
problem, that i have a phase transition between the frozen and the
normal tissue (The only difference between this regions is the
thermal conductivity).-> I don´t know the normal/frozen interface
a priori:-(
How can i define this problem in FEMLAB. Can i define variables which
are dependent on the solution (Temperature)???
thx and greetings,
Habakuk

Subject: Phase Transition (Freezing) in FEMLAB

From: Lars Gregersen

Date: 1 Dec, 2005 21:05:13

Message: 2 of 4

On Thu, 1 Dec 2005 07:42:50 -0500, Habakuk <gullwing@gmx.at> wrote:

>Hi to everybody!
>I´m a new Femlab user and I´ve following problem:
>I want to simulate a tip which freezes biological tissue. For this i
>use the Heat Transfer module (BioHeatEquation). Now i have the
>problem, that i have a phase transition between the frozen and the
>normal tissue (The only difference between this regions is the
>thermal conductivity).-> I don´t know the normal/frozen interface
>a priori:-(
>How can i define this problem in FEMLAB. Can i define variables which
>are dependent on the solution (Temperature)???

Yes, any parameter in your model may depend on other parts of your
model! Simply specify an expression that uses the dependent or
independent variables (e.g. 0.1*T^2-0,2*T).

E.g. you can simply enter an expression for your thermal conductivity
that depend on T. The ways to do this are usually 1) to enter an
expression directly, e.g. a polynomial or 2) to use a look-up table
(which is entered using the menu Options->Functions.

Depending on what exaclty you try to model you also need to take into
account that Cp changes as a function of time (and temperature). This
change may be used to take the latent heat into account.
  

  Lars

PS. FEMLAB has changed name to COMSOL Multiphysics.

Lars Gregersen
COMSOL A/S
http://www.comsol.dk

Subject: Phase Transition (Freezing) in FEMLAB

From: Habakuk

Date: 2 Dec, 2005 03:09:58

Message: 3 of 4

> Yes, any parameter in your model may depend on other parts of your
> model! Simply specify an expression that uses the dependent or
> independent variables (e.g. 0.1*T^2-0,2*T).
>
> E.g. you can simply enter an expression for your thermal
> conductivity
> that depend on T. The ways to do this are usually 1) to enter an
> expression directly, e.g. a polynomial or 2) to use a look-up table
> (which is entered using the menu Options->Functions.
>
> Depending on what exaclty you try to model you also need to take
> into
> account that Cp changes as a function of time (and temperature).
> This
> change may be used to take the latent heat into account.
>
>
> Lars
>
> PS. FEMLAB has changed name to COMSOL Multiphysics.
>
> Lars Gregersen
> COMSOL A/S
> <http://www.comsol.dk>
>

Thx for your fast and knowledgeably reply!
But why should change the volumetric specific heat with time? Is it
not a better method to consider the latent heat with a dirac pulse
(which takes effect at the phase transition =0°C)???
I´m not sure a hope to get an answer!
Greetings,
Habakuk

Subject: Phase Transition (Freezing) in FEMLAB

From: Lars Gregersen

Date: 3 Dec, 2005 09:58:13

Message: 4 of 4

On Fri, 2 Dec 2005 03:09:58 -0500, Habakuk <gullwing@gmx.at> wrote:

>> Yes, any parameter in your model may depend on other parts of your
[snip]
>> Depending on what exaclty you try to model you also need to take
>> into
>> account that Cp changes as a function of time (and temperature).
>> This
>> change may be used to take the latent heat into account.

>Thx for your fast and knowledgeably reply!

I work for the company that makes COMSOL Multiphysics (formerly
FEMLAB)!

>But why should change the volumetric specific heat with time? Is it
>not a better method to consider the latent heat with a dirac pulse
>(which takes effect at the phase transition =0°C)???
>I´m not sure a hope to get an answer!

Exactly. In order to take the latent heat into account you have one
curve that describes the change of the Cp value itself when you have a
phase change and a pulse that takes the latent heat into account -
this pulse enters your model in the same place where the Cp value
does.

I suggest you contact your local support if you need a specific
example.


  Lars


Lars Gregersen
COMSOL A/S
http://www.comsol.dk

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