[Gasification] tests to design a new cheap gasifier fan

Arnt Karlsen arnt at c2i.net
Sun Oct 3 10:40:16 CDT 2010

On Sun, 3 Oct 2010 03:33:27 -0700, jim wrote in message 
<AANLkTikOz+WreDSavhWYRXii-8MRSt0jXEvqvHu7Zsrc at mail.gmail.com>:

> the rotor made from the spinning disk with vanes between we have not
> yet tested.  we should i agree.  we have testing the one sided version
> with vanes at various angles forward and back from perpendicular.  i
> was surprised to find it makes little difference.  backward rake,
> espeically curve backwards at the tip is done with pro fans to reduce
> noise, not increase pressure/vac.  it actually reduces performance a
> bit.

..depends on how you define it, backwards bent blades get higher
efficiencies, as they move more gas for the same power input.
Forward bends get you more "gas speed" for the same wheel size 
and speed sacrificing efficiency, straight blades fall between 
these 2, and are the easiest ones to keep clean.
> it has taken awhile to get through my head that these fans are working
> as centrifugal devices, not pressure devices.  the blades are not
> levers or pumps.  they are simple accelerators for air mass.   your
> pressure/vac is coming from velocity and inertia/momentum.

..and your losses from boundary layer friction and 
leaks over the blade edges, easily 25%.

> this is why the tightness to the walls makes little difference.  i've
> moved the rotor / wall tolerance around quite a bit and saw very
> little diffference.  i've read this is also why you see less double
> walled rotors that one might expect.  but i've yet to test this so
> can't really say.  greg says he gets 25% more out of these types.
> some devices in the weed blower vac world put vanes on both sides of
> teh disk.  but i think this is to prevent the weeds from getting stuck
> on the back of the disk.  see the toro blower for example of this.

..and to provide "draft" for motor cooling.

> arnt raises an interesting concern about the rotor bending.  the other
> way to deal with this would be to make a full slot for the vanes, and
> push the vanes through so they stick out on both sides. put a hole in
> the center so air can feed to both sides of the rotor.

..balancing these, makes them safer, adding disks on each 
side only adds to this.  Another way is use a pipe as the 
fan shaft, and draw gas from one side and air from the 
other.  To make it wild, bend the blades backwards, ditch 
the center "back bone" disk and burn the gas mix _in_ the 
wheel... ;o) Heron did a similar stunt centuries ago. ;oD

..like I said, spin up your wheels in an _hefty_ safety cage 
with a stroboscopic light and cameras, and _compare_. ;oD

..med vennlig hilsen = with Kind Regards from Arnt... ;o)
...with a number of polar bear hunters in his ancestry...
  Scenarios always come in sets of three: 
  best case, worst case, and just in case.

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