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Phase change in a lake sediment

Posted 8 ott 2015, 06:34 GMT-4 Heat Transfer & Phase Change, Materials, Mesh, Modeling Tools & Definitions, Parameters, Variables, & Functions, Studies & Solvers Version 5.0 1 Reply

Jilip Jonrädd
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I'm trying to simulate a freezing process at the bottom of a lake and I want to include phase change of the sediment. I have been trying to implement it and at the moment it takes ages to simulate a 24 h freezing with 1 hour time step. How do I shorten the simulation time and correctly use the phase change physics?

I have attached the file!

I'm new to Comsol as well!

/Jilip

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1 Reply Last Post 8 ott 2015, 07:45 GMT-4
Thomas Schlech
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Posted: 9 years ago 8 ott 2015, 07:45 GMT-4
I don´t exactly know what you want to model, but i watched your model and have an advice. At first not about computational time but about your boundary conditions. If you model it like this with the fixed temperatures for boundaries youu have some dirichlet boundary conditions, meaning they won´t change. So according to your temperature gradient and thermal conductivity they will act like a heat source if you lower the temperature of the big block. The same is true for your water to clay boundary. I don´t know if this is wanted but just wanted to mention it.

In General Phase change Problems with the comsol function need a sufficient small time stepping and fine mesh for correct solution. The spatial temperature difference and the difference from one time step to the other shouldn´t be higher than your transition Intervall between Phase 1 to Phase 2. So if you want to improve computational time get sure about your dimensions of temperature Gradient and take sufficient high time steps.
I don´t exactly know what you want to model, but i watched your model and have an advice. At first not about computational time but about your boundary conditions. If you model it like this with the fixed temperatures for boundaries youu have some dirichlet boundary conditions, meaning they won´t change. So according to your temperature gradient and thermal conductivity they will act like a heat source if you lower the temperature of the big block. The same is true for your water to clay boundary. I don´t know if this is wanted but just wanted to mention it. In General Phase change Problems with the comsol function need a sufficient small time stepping and fine mesh for correct solution. The spatial temperature difference and the difference from one time step to the other shouldn´t be higher than your transition Intervall between Phase 1 to Phase 2. So if you want to improve computational time get sure about your dimensions of temperature Gradient and take sufficient high time steps.

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