On Jan 23, 2013, at 8:39 PM, John Assael wrote: > I think it its not a problem of properties as the same values are used in > COMSOL and they result different values. > Moreover, I tried small changes like 5-10% and there was no big difference...
If you drop tc0 by a factor of 2, you get pretty close to your COMSOL solution. I'm not saying that's what happened, just that this problem is pretty sensitive to the thermal diffusivity. > could it be FiPy's Solver? It could be, but I think it's unlikely. FiPy is subjected to thousands of tests, many of them much more rigorous than this fairly simple heat transport problem. I suspect that there is some unintended difference in the declaration of the COMSOL problem and the declaration of the FiPy problem. One issue is that your solutions are not converged. Changing the timestep changes the answer. If changing the timestep or the grid resolution changes the answer, then your timestep or grid spacing are too large. Your coefficients are all linear, so sweeping does not help, but dropping the timestep does. You might not need that much, but dropping timeStep by a factor of ten seems to give fairly converged results. Another thing that occurred to me is that you have declared the coefficient of the DiffusionTerm at cell centers, but FiPy needs it at faces. FiPy interpolates from cells to faces automatically, but the particular interpolation chosen can make a difference. When I started experimenting with different interpolations, I found that this simple rearrangement of your equation: heatEq = (TransientTerm(coeff=denCell*cpCell) == DiffusionTerm(coeff=tcCell) + QCell) is enough (combined with timeStep = 2e-4) to give pretty good agreement with your Experimental and COMSOL results: 0.002 0.530949358814 0.004 0.798725006713 0.006 0.981455545597 0.008 1.11988469053 0.01 1.23100247808 0.012 1.32361096122 0.014 1.4028708204 0.016 1.47206568877 0.018 1.53341163428 0.02 1.58847282845 This comes back to my original point about the sensitivity of this problem to the thermal diffusivity. By changing the interpolation of the DiffusionTerm, you change the thermal diffusivity at the wire/fluid boundary and so have a strong effect on the evolution of the problem. _______________________________________________ fipy mailing list [email protected] http://www.ctcms.nist.gov/fipy [ NIST internal ONLY: https://email.nist.gov/mailman/listinfo/fipy ]
