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Thomas, This slide show the findings that I consider most
significant (for my duct-design-dilemma (D^3)).. Skin friction and
separation both cause pressure loss and drag increase - however, separation is
by far the bigger cooling killer than skin drag. Also note - that
increasing the air velocity to delay separation will contribute to more
skin drag - but, I decided I did not care - because separation was the bigger
bad guy. I would make the skin as smooth as I could and that would have to
take care of minimizing skin friction.
So with that and old Mr. Bernoulli findings I decided a
pinch duct would:
1. Reduce the opening area more effectively than
what I would have to do with a truncated Streamline duct- thereby reducing
cooling drag.
2. Would increase the energy of the boundary layer thereby
permitting it to penetrate further into the expansion area before separation
occured.
3. Would fit my installation - a not insignificant
consideration in the decision.
oh, and most importantly:
4. Looked sexy, would raise a lot of questions and
make it look like I understood this stuff {:>)
Once again credit goes to Mr's K&W, Horner and a few
others.
Ed
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