OK, you seem to have two contradictory statements: The first paragraph
(correctly) states that the "carry" is related to the flow rate. But
then in the last paragraph (and the quote about Bernoulli) suggests that
the pressure _itself_ is responsible for carrying the particles. The
correlation that high speed == low pressure and vice versa (Bernoulli's
principle) is not really relavent, and for a ducted system, only
marginally applicable.

Yes, the pressure and flow rate do change (and you can use Bernoulli's
principle on a limited basis at the junction) when you change duct size.
But pressure is just a means to an end (in that pressure differences are
what move the air, of course). It is air speed that is responsible for
carrying the particles (turbulence and particle friction, in
particular). So when you say "Lower vacuum (large pipe), pieces drop" it
should really be "Lower speed...".

Greg

George wrote:
Well, fluid dynamics was not my prime concern. The concern was with the
"carry", which of course is related to the flow rate. You are concerned
with the fluid, I with the solid, which, at least to me, is the reason for
having a collector, not to move air around.

"Bernoulli's principle can be explained in terms of the law of conservation
of energy (see conservation laws, in physics). As a fluid moves from a wider
pipe into a narrower pipe or a constriction, a corresponding volume must
move a greater distance forward in the narrower pipe and thus have a greater
speed. At the same time, the work done by corresponding volumes in the wider
and narrower pipes will be expressed by the product of the pressure and the
volume. Since the speed is greater in the narrower pipe, the kinetic energy
of that volume is greater. Then, by the law of conservation of energy, this
increase in kinetic energy must be balanced by a decrease in the
pressure-volume product, or, since the volumes are equal, by a decrease in
pressure."


Will you go this? Lower vacuum (large pipe), pieces drop - higher vacuum
(narrower pipe) , pieces move.



"G. Lewin" wrote in message
...

This is, well, to be blunt, kind of gobbletygook. Well, the conclusions
are more or less valid (big pipe = high flow, low speed), but the
physical explanation is not correct.