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Bundle representation using Porous media

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Old   December 12, 2000, 05:50
Default Bundle representation using Porous media
  #1
Hooky
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Hi,

I have tried to simulate a bundle of tubes by using the porous media option. First I did a simple 2d case of a periodic part of the bundle as represented in the handbook (tutorial 3). I did several simulation for a range of inlet velocities between low velocity and maximum velocity (compared with the real geometry). From the data I am able to plot the relation between the free inlet velocity and the pressure drop. Using the Ergun equation it is possible to determine c2 and alpha (by using a parabolic trendline). The order of magnitude seems correct for both parameters but after simulation in the final geometry c2 is under extimated. Do you have any previous experience in this field and could you advice me on the procedure to follow?

Thank you for your cooperation.

Hooky
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Old   December 12, 2000, 22:48
Default Re: Bundle representation using Porous media
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Greg Perkins
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The Ergun equation may not be a good/the best equation to use to represent a bundle of tubes - since the equation is developed assuming a packed bed of spheres. Maybe consider another equation for representing the solid-fluid drag intereaction.

Greg
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Old   December 13, 2000, 00:57
Default Re: Bundle representation using Porous media
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Dan Williams
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Wow that sounds pretty convoluted. Couldn't you just define an source term for the momentum equation which has different resistance depending upon the coordinate direction. You can do this quite easily in CFX-5.
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Old   December 13, 2000, 01:01
Default Re: Bundle representation using Porous media
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Greg Perkins
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Its easy in Fluent too - I suppose the point is what form this source term should take!
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Old   December 13, 2000, 04:55
Default Re: Bundle representation using Porous media
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Hooky
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There are empirical relations to determine the pressure drop in a bundle of tubes but it is not possible to separate the inertial resistance from the viscous resistance. It is relatively easy to calculate the inertial resistance for a bundle of tubes and in most of the case it is pretty accurate. However I would like to have an idea of the viscous resistance effect on the flow. Now, how could this coefficient be evaluated?

Thanks

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