# residence time distribution

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 December 6, 2005, 03:49 residence time distribution #1 markus Guest   Posts: n/a 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?

 December 6, 2005, 09:58 Re: residence time distribution #2 Martin Guest   Posts: n/a 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

 December 6, 2005, 10:46 Re: residence time distribution #3 markus Guest   Posts: n/a 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

 December 8, 2005, 02:47 Re: residence time distribution #4 Martin Guest   Posts: n/a 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

 December 19, 2005, 06:52 Re: residence time distribution #5 zhixin huang Guest   Posts: n/a Hi... How to get residence time distribution in cfx-post? thanks.

 December 19, 2005, 12:48 Re: residence time distribution #6 markus Guest   Posts: n/a 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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