ORGLIST: Scale up and stirring

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From: Basil Fowler (bjfowler$##$
Date: Mon Nov 26 2001 - 17:25:17 EST

While I cannot give any specific help, I might mention a few points from =
experience in selling stirred reaction vessels.

To ensure proper mixing, the material has to move or be moved along a
combination of three axes;  axial, that is a horizontally circle centre=
d on
the axis of ratation of the stirring mechanism; radial, that is a horizon=
motion in a radial direction; and finally a vertical movement.

If the material is a low or medium Newtonian fluid, the wake left behind =
stirrer will provide axial and radial motion.  The centrifugal effects =
cause the material to pile up against the walls of the vessel, and to
equalise the pressure, a vertical circulation is induced.

When the material is non-Newtonian or viscous, the stirrers must be
explicitly designed to induce the radial and vertical motions.  For sti=
materials like greases, an epicyclic motion may be needed, where the radi=
of the stirrer continuously varies between two limits.

What you have to do is to establish what whether the vertical or radial
movement can be effected through pressure variations induced by the axial=
movement of the stirrer or if these movements have to be caused by an
explicit external influence.

Hope this helps

Basil Fowler


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