[TheForge] photos under "inexpensive recuperative forge"

[Jerry Frost]

Morning Mikey:

There is no need for a fan to make a recuperative wall 
furnace work. I haven't seen one patent drawing that 
relies on convection, (boyancy) fans or air jets to 
circulate combustion gasses through the gap. I've only 
looked at a couple dozen out of hundreds though so I'm 
sure they're out there.

The principle for circulating the exhaust gasses around 
the gap in all the patent drawings I've looked at use 
induction at the burner ports. The burner nozzle stops 
in the outer wall and fires across the gap through a 
port in the inner wall.

It makes the gap a low pressure zone and the furnace 
chamber a high pressure zone. You can put the entry 
ports anywhere in the furnace chamber you want. The 
exhaust port can also be placed pretty much at will but 
you have to consider the burner port and entry port 
placement or you'll short circuit the 
burn/recirculation/exhaust cycle.

Making a recuperative wall furnace circulate is no more 
complicated than making a naturally aspirated burner 
suck. It's exactly the same principle.

Frosty
-------------------------------
If it ain't forged
it ain't real.
Wrought iron is.
The FrostWorks

Meadow Lakes, AK.

http://www.artmetalradio.com/


From: "Michael" <michael.a.porter at comcast.net>


> Jeff,
> Yes there is such a design. We discussed it on this 
> list last summer. What
> you need for safety is to build the heat scavenging 
> into the forge body
> rather than into the burner. The only kind of burner 
> that will safely use
> preheated air is a nozzle mix type. By the time you 
> have gone to that much
> trouble in anything short of large industrial 
> equipment, you're working too
> hard (translate spending too much) on the problem.
>
> There are three practical paths to building a heat 
> recuperative craft forge.
> They can work on various heating equipment devices, 
> but would probably be
> best suited to heating ceramic chip media:
>
> (1)Design the body with double walls. Then, exploit 
> the power of buoyancy by
> placing the air entrance in the outer wall a good 
> deal lower than the air
> exit(into the fire-box) above the burner area, 
> employing a fan-blown burner
> that will produce a large secondary flame so that the 
> super-heated air has
> something to combust. The fan-blown burner is merely 
> used to create a more
> diffuse flame in order to avoid overheating the forge 
> structure in the
> combustion area; a poor naturally aspirated burner 
> design, which produces a
> large secondary flame will serve equally well. This 
> design requires no added
> power to move the superheated air itself and is 
> therefore the safest; it is
> also the least efficient.
>
> (2) Employ a fan in the bottom of the forge's inner 
> wall, in order to draw
> super-heated air down to the bottom of the fire-box 
> against the power of
> buoyancy, and inject the fuel into the fire box 
> (above the fan). The
> shortcoming in this design is the fan placement, 
> which would require it to
> be made of refractory materials. And spun by an 
> exterior power source; this
> should be a fun problem for electrical types to mull 
> over (of course, the
> fan could be sealed and use to push air in, which 
> brings us to solution
> three, below).
>
> (3) Inject compressed air into the top of the air 
> space between the forge's
> inner and outer walls , creating positive pressure to 
> push the super-heated
> air down to the bottom of the fire-box against the 
> power of buoyancy, and
> introduce the fuel in the fire box (above the fan) 
> from an injector tube.
> This also has some problems: The air must be 
> regulated to keep pressure from
> building past the ability of the refractory to 
> withstand it; a compressor
> must be running to provide the air.
> Mikey
>