[Gasification] blower suggestions?

[Daniel Chisholm]

On Tue, 2007-07-08 at 13:00 -0700, Mark Ludlow wrote:
> Lets assume that the fan is driven by an induction motor without
> brushes.

Probably not.  High pressure blowers (e.g. the shop vac or central vac
ones we're talking about here) need high tip speed in order to produce
high pressures (and tip speed goes as RPM times diameter).

The ones I've taken apart use universal motors (i.e. a brush motor like
you'd see inside an electric drill, circular saw, angle grinder, etc),
and turn (SWAG) 10,000-ish RPM.

The nice thing about universal motors is that you can control their
speed with a $7 light dimmer switch (within reasonable limits - it has
to be kept going fast enough to get adequate cooling air).

Whereas an induction motor is inherently a constant speed machine, and
its speed can't be cheaply and practically varied (which took me a while
to wrap my brain around - if you reduce the applied voltage, e.g. with a
lights dimmer, it won't slow down, but it will draw more current in
response, and overheat!)

A $20 Princess Auto special blower (almost certainly from a shop vac)
that I have had sitting on my bench forever, uses a centrifugal blower
wheel (approx 4" dia.) for moving its main charge, and uses a small
axial fan for its cooling air.  This would be a better one to use for
sucking on a gasifier than my house's central vac, which passes all of
its air through the motor.

Jim, have you thought about pushing your air through your system, rather
than pulling?  It's a tradeoff of course, it makes some things such as
sealing and fuel feeding more difficult, and others such as fan
selection easier.


-- 
- Daniel
Fredericton, NB  Canada