[Spridgets] Weber DCOE vs OER DCOE

Ron Soave soavero at yahoo.com
Sun Sep 27 05:27:18 MDT 2009


--- On Sun, 9/27/09, Robert E. Shlafer <pilotrob at webtv.net> wrote:
> "Reynolds Numbers" apply to liquids
> as far as I know (which is not that far in these respects)
> however,

Reynold's number applies to all fluids, air included. Off the top of my head at 6am - It is dimensionless, and is equal to the density times the velocity of the fluid times effective diameter of the fuid passage divided by the kinematic viscosity (rho*V*De/mu). For air, Reynold's number is used to calculate the friction factor, and that's equal to .046/Re^.2 if memory serves. The simplified form of Bernoulli in the case we are talking about is that flow: W=density * Area * velocity. As you can see, there are common terms in each equation, so you can manipulate them to come up with a friction factor, but that factor will only tell you the friction per unit length, hence my "nope". In fact, the throat reduction here makes the air behave somewhere in between a swage and a sudden contraction. In both cases, the friction factor varies non-linearly with the ratio of the upstream and downstream areas. You want to keep it gradual, with a reduction angle of less
 than seven degrees for the inner edge of the boundary layer of flow. Throw in additional effects of non-uniform flow fields due to the contraction and the effect on the vena-contracta in the venturi throat and the homogeneity of the flow and downstream mixture suffer.

Or you could switch back to SUs.

Off to the races,
Ron


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