[Stoves] Rapid mixing

Crispin Pemberton-Pigott crispinpigott at outlook.com
Tue Sep 27 22:09:54 CDT 2016


Dear Kirk

 

I think your conclusion is correct - that you can shorted the height of the
combustion zone with radial or helical mixing.

 

I provide two photos with this in mind, though accomplished in completely
different ways. The first is (for a wood burner, not pellets) is to put the
mixed below the fuel, to continuously create a series of ‘induced
vortices’ a few of which pass through the fuel and provide mixing by
spinning. A vortex tends to perpetuate itself so all that is needed is to
get a few going all the time.

 



The material is a low chrome stainless steel. The production is in three
stages: blanking, punching the cuts, then forming.

 

The second method of shortening the flame is to use the secondary air
entering the fire as a method of driving the flames horizontally. This
should be done in a ‘divided’ manner, not a ring of air, so that it
breaks up the rising gases into manageable jets. This kind of short clean
burn can only be done with preheated secondary air - 300-500˚C works well.

 



 

The fire above is burning pellet gas (as a TLUD) though it also works for
wood if the gas generation is consistent. Consistency requires very good
air control. The amount of is required to achieve this is so low that it
pretty much rules out having an open bottom with fuel sticking out. 

 

Readers may recall Julien in Coburg combined the injection of air and
placement of the air feed in the gas stream. A problem commonly reported
with that approach is the cooling of the metal by the air can interfere
with the combustion.

 

Readers may also recall Dr Nurhuda in Indonesia achieved a downward turning
flame consistently in his recent stoves reducing the flame height basically
to zero. All of these approaches can assist the provision of lower height
stoves - a major challenge for typical Indian rural households where cooks
won’t compromise on the cooking height. 

 

Everyone should try these approaches and report what works well. 

 

Regards

Crispin

 

 

 ……

Not to be distracted from the purpose of this list, I have a thought about
wood stoves.  A small natural draft wood burning cook stove that mixes the
wood gas with secondary air in 2 cm has a considerable advantage over a
stove that may take 20 cm or more.  It's a little like transistors, which
gave advantage over vacuum tubes in electronics.  Rapid mixing can enable a
small wood stove to burn quick and clean at both high and low power levels.
Witness the excellent numbers for the Wonderwerk TLUD-ND stove which uses a
rapid Venturi mixing technique.  Combined with the user friendly power
level controls, the principles used in the Wonderwerk stove hold
considerable potential.  Rapid mixing seems to me to be a very good area
for research.  I wonder how many rapid mixing techniques will be found over
the next few years?  I intend to contribute.

 

List, keep writing about wood stoves, don't be distracted.

 

Kirk H.

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