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</o:shapelayout></xml><![endif]--></head><body bgcolor=white lang=EN-CA link=blue vlink=purple><div class=WordSection1><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Dear Alex<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>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).<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>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%.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>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.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>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.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Regards<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Crispin<o:p></o:p></span></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>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.<br>Certainly a flow restriction, but with the increased space you describe in you example, a tolerable one?<br><br>Alex<br><br><br><o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p></div></body></html>