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Mohit May 1, 2004 12:10

Hello all,

I am a Chemical engg student at IIT delhi and am working on determining the residence time distribution of laminar flow in helical tubes.

I have tried using the DPM model. Injecting inert particles at the inlet and monitoring their flow at the outlet using discreet phase sampling. But the process takes lot of time and is not accurate.

I want to know how can I use the species model to give a pulse input of a tracer at the inlet and how can I monitor its flow at the outlet.

Regards mohit

zachi May 10, 2004 09:43

Re: RTD by CFD
Yes it will take a longe time depending on the length of your geometry. I think the species methode will last much longer! Are you sure your flow is laminar and there is no backmixing! Which density are your inert particles of!?...



Mohit May 10, 2004 09:52

Re: RTD by CFD
The inert particles are of the same density as the fluid (1100 kg/m3). yes the flow is laminar. please let me know how to do it using the species model.

regards mohit

zachi May 10, 2004 10:08

Re: RTD by CFD
enable multiphase species, define species, define inlet of the species, unsteady calculations. Iwould say it is much more work to calculate RTD with the species model than working with DPM!

What is your geometry length and which model do you use for your calculations. Wher is your injection point or surface?



CFD Newbie May 10, 2004 10:46

Re: RTD by CFD
Hi zachi,

Can you tell me if it is possible to get RTD in a steady state simulation? And if so how can this be done?



zachi May 10, 2004 10:55

Re: RTD by CFD
Using the DPM (discrete phase model) in fluent enables you to calculate a RTD in a steady state solution!

Compute your flow pattern Enable DPM Create your particel injection define your particles create a control-face report--> discrete phase--> sample!! Fluent will create a *.dpm file in which the passing time of particles at the control-face is recorded!



mohit May 10, 2004 17:30

Re: RTD by CFD
hi zachi,

my geometry length is 0.2 m with mean velocity of 0.15 m/s . my model is laminar& segregated. i inject at the velocity inlet using sueface injetions but i dont know how to inject a species as we inject particles

please reply soon regards mohit

zachi May 11, 2004 03:03

Re: RTD by CFD
You will have to create separate a fluid zone in which the species is injected and you must use unsteady calculations you will be able to create a monitor recording the flux at a defined control face or the outflow face! By using the outflow face you have to observe that you do not have any recirculations in your flow pattern!! I would do RTD calculations with DPM!!



ryan May 12, 2004 19:35

Re: RTD by CFD
I prefer to use the pathlines function (under Display) for this purpose, since the pathlines are assumed to be massless. You can adjust the number of pathlines released from a surface using a surface rake. Otherwise you're limited to the number of cells at the release surface.

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