[Stoves] burning wood gas

[Gordon West]

A number of years ago a retired fluid mechanics scientist/engineer visited the shop and saw some of our attempts to mix air with smoke, most of them involving swirling. He explained to me that swirling is not very effective because it doesn’t do much to disturb laminar flow - unless you put some obstructions in the flow of the swirl. He said that the basic principle of mixing fluids is to make them go around 90 degree corners. 

I see in Kirk’s designs a lot of going around corners, which seems to be where the best mixing effects are showing up. Something like putting tabs in a swirl would probably mix well and extend the time of mixing as opposed to a shorter path of the simple direct rising draft of gases. Other important refinements relate to controlling the shape of the resulting flame, for which the cones and such come into play.

Optimizing the air/fuel mixture in an adjustable power scenario without combustion gas sensors and feedback loops and powered combustion air will probably be a guessing game without a good deal of expensive gear and real data collection. Variability from feedstock type and quality is a constant, so there can be no high degree of precision in control - the question is, what degree of control is necessary? My guess is that for simple stove technology the test is: "if it looks good, it’s probably pretty good."

Gordon 









> On Jul 20, 2021, at 6:37 AM, ajheggie at gmail.com wrote:
> 
> 
> 
> On Mon, 19 Jul 2021 at 23:11, Daniel Pidgeon <daniel.pidgeon at hotmail.com <mailto:daniel.pidgeon at hotmail.com>> wrote:
>  Or was the swirl discarded as a lesser form of mixing than the Venturi effect?
> 
> I used to use a swirl/vortex in my forced draught devices and see no reason to believe it is the most efficient means of mixing, the mixing tends to occur at the shear face between two gases but the energy is still used in creating the vortex and very little is available from the buoyancy effect of the flue gases with no fan.
> 
> I would have liked to pursue other ways to create movement of gases, like the steam aspirator but my poor engineering ability limited me.
> 
> Andrew
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