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Old   October 19, 2003, 14:06
Default Boundary conditions for stirred tank
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Dear friends,

I have a question about the boundary conditions of stirred tank with baffle and six blades. In reality, there is no input and output of fluid in the mixing tank once the fluid is hold in the tank. However, I am not sure whether I can use free-slip wall boundary condition for the top liquid surface such that there is no Inlet and Outlet boundary conditions in the whole domain. I will set the pressure profile in the initial conditions.

Any suggestion is appreciated.


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Old   October 19, 2003, 14:41
Default Re: Boundary conditions for stirred tank
Jim Park
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First, this problem was a demo for CFX-4 for a long time. I'd try them (see the code listings elsewhere on this web site) for hints. Look for "stirred reactor."

I don't know how the blades might be positioned, but it's not too hard to see the fluid being lifted by a blade with an angle of attack, causing local (and time-dependent) bulges in the fluid surface. Even if the blade flat is vertical, the fluid will be thrown outward to the wall of the vessel. Continuity requirements will cause the fluid to rise along the wall, lifting the fluid surface locally at the wall.

Therefore I would guess that you need VOF or another free surface simulation tool. With a liquid below and a gas above (air?), I'd first try just ignoring the lighter fluid completely (treat it as a constant pressure on the liquid) with no shear stresses on the liquid at the surface.
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Old   October 20, 2003, 13:21
Default Re: Boundary conditions for stirred tank
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Thank you, Jim. You comments help me very much!

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