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-   -   residence time distribution (http://www.cfd-online.com/Forums/cfx/21907-residence-time-distribution.html)

markus December 6, 2005 02:49

residence time distribution
 
Hi... I want to use a Particle Tracking approach to obtain the RTD of a vessel based on a steady state simulation. When doing this the mean residence time gets way to high. I used small particles with a density of 1 and added turbulent dispersion. I am not sure about adding additional forces.

Any hints to the problem or another suggestions on how to obtain a "lagrangian" residence time distribution?


Martin December 6, 2005 08:58

Re: residence time distribution
 
it it much easier to implement an Additional Variable "RDT" with unit [s] and transport equation. RDT is set "0" at all inlet.

Then you create a subdomain "RDT sub" over all and impement a source for RTD with 1 [s/s]. Now RDT will become greater with resident time.

bye martin


markus December 6, 2005 09:46

Re: residence time distribution
 
I aready tried the implementation of an additional Variable RTD. Analysing the spatial distribution of RTD at the outlet of my reactor gives the right mean residence time, but just a rough approximation of the distribution (too coarse grid??) and a too narrow distribution (probably due to numerical diffusion effects). That why this approach seems not very powerful to me.

markus

Martin December 8, 2005 01:47

Re: residence time distribution
 
your particle tracking can't be better than your grid - so this would be the problem with your results. Diffusion effects shouldn't be if you use ADVECTION SCHEME: high res


zhixin huang December 19, 2005 05:52

Re: residence time distribution
 
Hi... How to get residence time distribution in cfx-post? thanks.

markus December 19, 2005 11:48

Re: residence time distribution
 
I'd run a transient simulation with a frozen flowfield where you solve a transport equation for an additional variable (scalar). Use pulse or step input and then monitor the massflow average of this quantity over time at the outlet.

markus


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