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Old   September 9, 2007, 22:54
Default urgent: diffusion simulation
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I am doing modeling of a diffusion process and I get the AMG solver error- species. I have a large volume at the base that is specified with a fixed value of all air, then from this base are a number of small channels initially with helium. At time zero the helium is at elevated temperatures where different sections vertically are specified with different temperatures where the lowest section closest to the base volume is hotter, then as the channel goes up, the sections are less hot. At time zero the air is allowed to diffuse up through the helium.

I have specified polynomial fcns for the diffuion coefficient and the gas properties as functions temp. I use underrelaxation values of .25, I use the NITA time advancement. I use time steps of 0.1 sec. I get the error after around 100 timesteps.

For a similar model it works. IN the simpler one it is a constant flow area for diffusion going up and the vertical sections are hotter as they go up.

Any ideas??? thanks so much
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Old   September 10, 2007, 10:40
Default Re: urgent: diffusion simulation
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I noticed in the run that it appears the temperature goes weird first. As it is running I get the warning that the temp has been limited to 1.0 in a number of cells. I also get cells that increase a lot in temp.

It also happens where for awhile it looks good, I get slow species diffusiona and slow energy diffusion, then within .3 seconds the entire model has a more or less equal temperature. If i do the run without species diffusion, just the different tempearture layers, it works fine.

any ideas? thanks
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