[Stoves] Improving Thermal Efficiency (TARP-VE)

[Crispin Pemberton-Pigott]

Dear Alex

 

>From my thinking along those lines, I came to the conclusion that if there
are still-hot molecules around at the edge, which is the case with most
charcoal stoves, the plot is already lost. The creation of a
hottest-point-at-the-centre with the longest travel path possible under the
pot, coupled with the anything that could be gained by radiation, was the
thinking behind the POCA layout. The 'concentrator' ring used I the Vesto
coal stoves and John Davies' coal gasifier enhance this effect (limiting
radiation in both cases being a minor loss).

 

In the POCA the gases are guided by secondary air into a central cone with
the point just touching the centre of the pot. Then the gases run
horizontally to the edge, leaving as cooled as they can be. At low power the
efficiency is over 60%.

 

I think it is worth trying your extension idea however. It would act as a
fin, a long circular one, picking up heat as the hottest remaining molecules
are forced to go under and up the other side by the draft. If it works, then
the calculated optimisation would be based on how far and fast hot molecules
can rise to overcome the downward forces of turbulent flow.

 

All things considered, there is a lot to be said for changing the pot (i.e.
putting on fins) which Dale Andreatta has pretty comprehensively
demonstrated. Even one at the edge would be an improvement. Are there any
traditional pots made on this basis? The would probably have to have been
cast as spinning a pot with a bottom lip leaves an unsanitary joint in the
corner.

 

Regards

Crispin

 

Anyhow, would it follow that a small rim extending down on the outer edge of
the pot bottom would prevent hottest gas molecules from slipping up the side
of the pot before it had given up its heat and dropped low enough to pass
under and around the rim edge. This is a bit like trapping supper heated
steam in an airless drier.
Certainly a flow restriction, but with the increased space you describe in
you example, a tolerable one?

Alex




 

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