> > Perform the following simple experiment: Take a long narrow soda
> > straw. Fill it with a combination of air bubbles and water/Bier/soda
> > or whatever.
> >
> > Case 1: Hold the straw above the glass.
> >
> > Case 2: Submerge the bottom of the straw straw in the liquid in a glass.
> >
> > In which case is the flow the best?
> >
> > This experiment in mostly relevant at startup, where it takes a while
> > for the oil pump to biuld up pressure, and shutdown, where the
> > turbo will keep spinning for a while after oil pressure has gone down.
> >
> > /martin

> Apparently to Martin, it was completely self explanatory.  I'm still
> blowing through that straw . . .

Ok, the key observation is that through the drain line will be coming
not only oil but also bubbles and foam (a mix of oil and small bubbles).
So the average density (specific weight) of the content/foam in the
return line will be less than that of the settled oil in the oil
pan. The density of oil is just below 1kg/dm3. Assume the density
of the foam is 0.1kg/dm3. If the oil return is submerged 1cm below
the oil level in the pan, there will be 9cm of foam standing still
above the oil level in the no pressure condition. At startup, and
during running it will generate back pressure when this foam
pillar has to be pushed below the oil level when, in the case
where the return is just above the oil level, the foam/oil in the
oil return would flow freely with no backpressure.

/Martin
--
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Martin Jagersand                 email: jag@cs.yale.edu
Computer Science Department             jag@cs.rochester.edu
Yale University

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