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Dealing with circular variable dependency and temperature dependent thermal properties

Posted 25 gen 2017, 15:26 GMT-5 Heat Transfer & Phase Change, Studies & Solvers Version 4.4 2 Replies

Bryan Burk
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Hello,

I am designing a heat exchanger in Comsol without actually modeling the fluid. I model a single channel and I am tracking fluid temperature and properties using variables. One specific example is as follows.

Specific Heat (Cp) is looked up with an interpolation function in which fluid temp and pressure are arguments [eg. Cp(T_fluid, P)]. Fluid temperature changes along the axial length of the exchanger in a way dependent on the Cp at any given point. This gives circular dependency.

Right now I start by solving the problem with a constant Cp. I find the fluid temperature at every 'y' location along the axis of the channel and then create a new Cp function in which the argument is y. I physically input that into the model and then solve again. The problem is that I must do this many times for different channel lengths.

I have seen mention of using ODEs and/or iterative solvers, but I can't find a resource showing how to implement those.

Can you help me?

Bryan
2 Replies Last Post 30 gen 2017, 18:08 GMT-5
Henrik Sönnerlind COMSOL Employee

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Posted: 8 years ago 25 gen 2017, 16:28 GMT-5
Hi,

Here is an example from another physics field:

www.comsol.com/model/modeling-stress-dependent-elasticity-14441

Regards,
Henrik
Hi, Here is an example from another physics field: https://www.comsol.com/model/modeling-stress-dependent-elasticity-14441 Regards, Henrik
Bryan Burk
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Posted: 8 years ago 30 gen 2017, 18:08 GMT-5
Hi Henrik,
I'm trying to extrapolate this to a three dimensional situation but am having trouble. It's unclear from the earlier example how to modify this to work in other situations. Do you know of any examples of that? This perhaps all stems from my lack of understanding about weak formulations of equations.

Thanks again,
Bryan
Hi Henrik, I'm trying to extrapolate this to a three dimensional situation but am having trouble. It's unclear from the earlier example how to modify this to work in other situations. Do you know of any examples of that? This perhaps all stems from my lack of understanding about weak formulations of equations. Thanks again, Bryan

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