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Stirred Tank with Scraper + impeller?

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Old   February 28, 2020, 12:13
Unhappy Stirred Tank with Scraper + impeller?
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Bruna Conrado
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Hi everyone,

I'm currently working on my thesis and plan to model a real mixing process (more specifically a shear rate analysis) on a real 4 L stirred tank. However, I'm relatively new to CFD and have so far only done very simple and quick tutorials and processes for my classes.

I'm really struggling because my tank has not only an impeller, but also a scraper to ensure proper solid dispersion, both rotating around the same axis, but at different speeds. The usual approach would be MRF, but I'm afraid my scraper geometry is too complex and overlaps with the impellers. (I've attached a draf of the geometry in this post)

All the literature I've found so far is of stirred tanks with a combination of impellers and baffles, none with actual scrapers. Which model is the most recommended for the tank I'm working with? Would it still be possible to use MRF (drawing multiple cyllindrical fluid domains) or would the results be too poor?

Any tip on which direction to go/which papers to read would be appreciated!

Thank you
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Old   March 1, 2020, 05:28
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You can still use the MRF process. Most of the user cases or tutorials use a geometry where it is rather trivial to separate moving and stationary zones. But the reality is that it is all about separation. And the only requirement is that the outer surface of the MRF should always be a surface of revolution.

So, in your case, if you use a straight, vertical cut you find that the scrapper and impeller are overlapping, so, you need to use a cut that is not vertical. Use a zig-zag cut. That is perfectly acceptable as long as the surface is a surface of revolution.

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mixing tank, multiple reference frames, scraper, sliding mesh model, stirred tank

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