wwd@netheaven.com wrote:
> In <list-1330568@skylee.com>, on 10/14/01
> at 09:36 AM, "J. Forster" <jfor@onemain.com> said:
>
> >Cavitation is when the pressure in a fluid
>
> edit_out [bubble] edit_out
>
> >goes down and a bubble
> >spontaneously forms and then collapses. It is typically found in pumps,
> >ultrasonic cleaners, and near propellers in water. The conditions in the
> >cavitation region are extreme and can erode nearby materials. In fact,
> >there was a Scientific American article about these bubbles emitting
> >light.
>
> >Electrolytic action is electro-chemical material removal or deposition
> >(like plating). An electrolytic cell can be formed by dissimilar metals.
>
> >-John
>
> When the bubble forms on the metal surface, molecules of the metal are
> 'sucked' off since the bubble is actually a vacuum.
I very much doubt that metal is "sucked off" since the maximum negative pressure
possible is 1 atmosphere. The compressive forces are almost unlimited, but
tensile forces are not, foer this reason.
> The bubbles travel off somewhere and more are formed, usually at a pit or
> protrusion in the metal
> surface.
So called "nucleation points". These are the starting points for bubbles. They
are also the starting points for bubbles in boiling fluids. If you microwave
water in a clean container and let it cool, you can reheat an then superheat it.
Any disturbance will then cause it to explode, throwing boiling water out of the
container. The reason is the first boiling removed many of the nucleation
points, so there was no place for the bubbles to start forming. This permits the
superheating of the liquid. Don't do it. Stir well between heatings.
> The erosion is therefore continuous for a given set of conditions. Better prop
> shape and material, polished and painted surfaces as well as reduced rpm's
> will help minimize this
Good surface finish would reduce the number of nucleation points, and therefore
tend to reduce cavitation.
-John
>
>
> Bill
> --
> -----------------------------------------------------------
> wwd@netheaven.com
> -----------------------------------------------------------
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