Whoa! Slow down, everyone. Let's back up.

The most important governing equations here are the incompressible
Navier-Stokes equations. The Bernoulli equation, as noted, is for
frictionless, incompressible fluids (n.b., both liquids and gases are
classified as fluids). The Euler equations are for frictionless,
compressible gases, but air under these conditions is nearly
incompressible, so we can make that simplification (if you want to get
an anser down to the 1% error range, use the full compressible N-S).

As pointed out elsewhere, Boyle's Law is just a simplification of
compressible gas laws, and isn't appropriate here.

Now, the solids in the airstream don't substantially affect the flow.
That means that we can "decouple" the system and calculate how "pure"
air would flow and then throw the wood dust/small chips in and simply
track them through the ducts, using our solution for pure air. (again, a
prefect model would account for the fact that the wood chips can _cause_
turbulence, but this is a secondary effect).

Now, as for the important answer of which is more important for moving
chips: turbulence effects vs. friction effects? I can't say. But if you
work through the calculations, you find that the "recommended" flow
speed usually works out to the transition region between laminar and
turbulent flow. Coincidence? I suspect (and this is pure conjecture)
that some amount of turbulence is necessary to keep dust from sticking
to the sides of the duct. Obviously, though, the bulk motion of the air
is what moves the dust from A to B.

Greg


Todd Fatheree wrote:
"Dave Hinz" wrote in message
...

On Thu, 22 Jul 2004 10:21:13 -0400, George george@least wrote:

Nope, Newton.

We're moving solids, hopefully. That's Newton. Thus the concept

passage

cited.

Solids suspended in air perform as a fluid, do they not?


I guess we need to find out which laws apply to a non-colloidal suspension.
By the way...the Bernoulli equation is for frictionless, incompressible
flow. It works well enough for fluids, but it's out for gases. A cursory
look over my fluid mechanics info says that we might have better luck with
the Euler equation.

Also, someone here pointed out that Bernoulli was Swiss (after someone else
said he was Italian). He lived much of his life in Switzerland, but he was,
in fact, Dutch.

todd