# transient diffusion convection

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 June 26, 2003, 09:34 transient diffusion convection #1 Volker Göke Guest   Posts: n/a Hi CFX 5.6 world! I've modelled the following problem successfully for the stationary case but have no idea how to work in some transient modifications: Object: Rectangular Parallelepiped (20* 20* 50 mm(height)) with a capillary tube (right-angled to one side wall) some millimeters above the bottom. Fluid domain - so far only one, Fluid model : variable mole fraction, isotherm 2 Inlets (Bottom, Top) 1 Outlet (Capillary tube) The composition at the two inlets differs (otherwise no diffusion due to concentration gradient - okay?!) Result:A relative sharp z-gradient on the level of the capillary tube. Also transport occurs in x and y direction. Now the real problem: The bottom inlet isn't usefull anymore. But I would like to start the simulation with an initial concentration distribution (only depending on the z-coordinate). A step function (any height from the bottom th the top should be possible) would be enough for the first guess. How can I implement this? - even sleeping on the manual wasn't successful! Thanks for all helpful hints! Volker

 June 26, 2003, 16:20 Re: transient diffusion convection #2 Phil Guest   Posts: n/a Step functions are easy with CEL. The bump tutorial has an example of using a step function to initialize variables (in that case, it is used to initialize volume fraction for a free surface calculation).

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