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.