Learning Forum

[mech]

I am modeling the heat transfer into a section of tissue using Pennes Bioheat Equation. This equation is similar to the 3D transient heat conduction equation, except there is an additional term that is dependent on tissue temperature, making it of the following form:

Where rho, C, K, A, and q are all constants.

Is there any way to change the governing equation in ANSYS Mechanical to include this term? If not is there any other ANSYS software that would be able to tackle this problem?

[Rob]

Please can you post an image of what you're trying to do? Ie is the heat transfer solid-solid or solid-liquid? 

[mech]

Here is an image of the tissue section I'm trying to model. The heat transfer is entirely conductive through the solid, although there is a convective boundary condition on the upper surface. I'm applying a constant heat flux through the recessed area and am trying to see how that changes the tissue temperature profile over time.

[Sandeep Medikonda]

Hello, I don't this is possible through mechanical. 

You would have to use the user programmable features. Checkout usercv or userfx in the manual.

Regards,

Sandeep

[Karthik R]

Hello,

You can solve this problem in ANSYS Fluent. You can set up your regular conduction equation (please remember to switch off your flow) in Fluent. You can use an User Defined Function (UDF) to input your temperature dependent source term. This source term will have to be volumetric and there are several examples of implementing this in the Fluent Customization manual. You can set-up the other boundary conditions (convection and heat flux) very similar to a steady state or transient thermal package. You can either solve this model as a steady state or transient in Fluent and analyze your simulation results.

Please let me know if this is an acceptable solution and I can point you to some resources in order to successfully model this problem. I hope this helps you.

Thank you.

Best Regards,

Karthik 

[mech]

Hello Karthik,

Your proposed solution would definitely be acceptable. If I understand correctly modeling the heat generation as volumetric, temperature dependent source term would be functionally equivalent to solving the PDE with the temperature dependent term in it. I'd appreciate any resources you have for modeling this problem, especially for the writing of the UDF.

Thank you

[Karthik R]

Hello,

For the UDF on volumetric temperature dependent source term, please refer to the Fluent Customization manual. There are lots of examples in the manual which might help you write one. The best way to get a functional UDF would be to use an example and modify it for your needs. I'd like to particularly point you to section 2.3.36 DEFINE_SOURCE (Fluent Customization Manual, R18.2). You can use this macro to define your source. Please refer to the examples in this section. I hope this helps.

Best Regards,

Karthik