A question about the Modelling of a Channel
 

Hello again,

I am modelling a channel with the properties below;

There is a carrier flow in the +x direction with solid particles inside. And there is a cross flow (of the same fluid) without particles in the -z direction. So, with the effect of the cross flow, the particles in the carrier fluid are moved to the direction of -z (to the accumulation wall) and of course at the same time in the +x direction by the carrier flow. So, I have to analyse those solid particles in the carrier flow.

For this reason, I used Lagrangian Model and I got some good results. My design of channel is right and I get right results.

But for very small particles (less than 10 micron), I have to consider also another phenomena, but I have difficulties in adding this phenomena to the model. It is that;

This cross flow is called field. So, there is FIELD-DRIVEN TRANSPORT in the -z direction. And there is DIFFUSION-DRIVEN TRANSPORT in the +z direction. For bigger particles, diffusion driven transport is neglected and I have already modelled them but for small particles the influence of this diffusion driven transport make the result totally the opposite to other case, so can not be neglected. So, I need to add this to the model somehow. I tried some solutions that came to my mind but they did not give the needed results.

If you know with which feature of STAR-CD I can model it pls. tell me. The problem is that I have only one month to finish my thesis and if I can not find this solution I will need to prolong it one more semester and I really do not want it.

Thanx in advance, selen

Answer
 

For the diffusion of the smallest particles, you can may be neglect them in the lagrangian phase and model them as a scalar in the carrier and see how this scalar diffuses in the continuous carrier phase. This way you may as well specify your diffusivity using user coding.