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</o:shapelayout></xml><![endif]--></head><body bgcolor=white lang=EN-US link=blue vlink=purple><div class=WordSection1><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Dear Paul<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'>It is entirely fair to call an unmixed flame dirty. It emits fine black carbon, much of it in the PM2,5 range and therefore breathable. There is still some hydrogen in the soot, so you essentially have a polyaromatic hydrocarbon (PAH). Those are the chemicals we now know gave the little chimney sweeps scrotal cancer – the first identified link between cancer and industrial malpractice. And rather than using a spoon to detect the carbon, use a white plate at an angle above the candle flame. The spoon heats rapidly, and you lose the thermal diffusion capture mechanism; the plate stays cooler longer and thermal diffusion plays an ongoing role.<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'>Thermal diffusion is also called thermophoresis – there is a slightly useful Wikipedia article <a href="https://en.wikipedia.org/wiki/Thermophoresis">https://en.wikipedia.org/wiki/Thermophoresis</a>. If you establish a thermal gradient in a fluid, the heavier species in the fluid will acquire more kinetic energy than the lighter ones and will move down the gradient towards the cooler surface. The effect was used early in the Manhattan project to enrich uranium isotopes.<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:10.0pt;font-family:"Arial","sans-serif";color:#1F497D'>Prof Philip Lloyd</span><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:10.0pt;font-family:"Arial","sans-serif";color:#1F497D'>Energy Institute</span><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:10.0pt;font-family:"Arial","sans-serif";color:#1F497D'>Cape Peninsula University of Technology</span><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p></o:p></span></p><p class=MsoNormal><span lang=EN-ZA style='font-size:10.0pt;font-family:"Arial","sans-serif";color:#1F497D'>PO Box 1906<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-ZA style='font-size:10.0pt;font-family:"Arial","sans-serif";color:#1F497D'>Bellville 7535<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-ZA style='font-size:10.0pt;font-family:"Arial","sans-serif";color:#1F497D'>Tel: 021 959 4323<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-ZA style='font-size:10.0pt;font-family:"Arial","sans-serif";color:#1F497D'>Fax: 086 778 0257<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-ZA style='font-size:10.0pt;font-family:"Arial","sans-serif";color:#1F497D'>Cell: 083 441 5247<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-ZA style='font-size:10.0pt;font-family:"Arial","sans-serif";color:#1F497D'>PA: Nadia 021 959 4330<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><div><div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0cm 0cm 0cm'><p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif";color:windowtext'>From:</span></b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif";color:windowtext'> Stoves [mailto:stoves-bounces@lists.bioenergylists.org] <b>On Behalf Of </b>Paul Medwell<br><b>Sent:</b> 10 January 2016 02:53<br><b>To:</b> Discussion of biomass cooking stoves<br><b>Subject:</b> Re: [Stoves] venturi system -ratios of air and gas?<o:p></o:p></span></p></div></div><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal style='margin-bottom:12.0pt'>Sorry to protract this discussion, but...<br><br>It is not entirely fair to call a nonpremixed flame "dirty". A nonpremixed Bunsen burner flame is typically yellow, caused by the presence of in-situ soot. However, very little of that soot is released from the flame. There are enormous differences between soot in a flame and soot emitted from a flame.<br><br>The candle is a classic example. Its primary purpose is to generate soot -- without soot in a candle flame it would emit very little light. Comparatively little of the soot that is generated is actually emitted from the flame. Next time you are at a fancy dinner, place you spoon above the flame and see how much soot is released: there will be some, but surprisingly little. Put your spoon in the flame for the same amount of time and you'll soon see how much soot is within the flame.<o:p></o:p></p><div><p class=MsoNormal>Soot within flames is often highly desirable: it is one of the primary mechanisms for heat release. A typical furnace runs nonpremixed flames for the sole purpose of generating as much in-situ soot as possible to radiatively heat the furnace.<br><br><br>On 9/1/16 5:18 PM, Philip Lloyd wrote:<o:p></o:p></p></div><blockquote style='margin-top:5.0pt;margin-bottom:5.0pt'><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>There is quite a good pic of flames at various mixed levels in <a href="https://en.wikipedia.org/wiki/Bunsen_burner">https://en.wikipedia.org/wiki/Bunsen_burner</a>. When there is no premixing, the flame is yellow and dirty (not all carbon is combusted, as in a candle flame). When you get to a stoichiometric flame, all the combustion takes place at the blue cone – the almost invisible “flame” above it is mainly hot gas radiating; minimal combustion takes place there.</span><o:p></o:p></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'> </span><o:p></o:p></p><p class=MsoNormal><span style='font-size:10.0pt;font-family:"Arial","sans-serif";color:#1F497D'>Prof Philip Lloyd</span><o:p></o:p></p><p class=MsoNormal><span style='font-size:10.0pt;font-family:"Arial","sans-serif";color:#1F497D'>Energy Institute</span><o:p></o:p></p><p class=MsoNormal><span style='font-size:10.0pt;font-family:"Arial","sans-serif";color:#1F497D'>Cape Peninsula University of Technology</span><o:p></o:p></p><p class=MsoNormal><span lang=EN-ZA style='font-size:10.0pt;font-family:"Arial","sans-serif";color:#1F497D'>PO Box 1906</span><o:p></o:p></p><p class=MsoNormal><span lang=EN-ZA style='font-size:10.0pt;font-family:"Arial","sans-serif";color:#1F497D'>Bellville 7535</span><o:p></o:p></p><p class=MsoNormal><span lang=EN-ZA style='font-size:10.0pt;font-family:"Arial","sans-serif";color:#1F497D'>Tel: 021 959 4323</span><o:p></o:p></p><p class=MsoNormal><span lang=EN-ZA style='font-size:10.0pt;font-family:"Arial","sans-serif";color:#1F497D'>Fax: 086 778 0257</span><o:p></o:p></p><p class=MsoNormal><span lang=EN-ZA style='font-size:10.0pt;font-family:"Arial","sans-serif";color:#1F497D'>Cell: 083 441 5247</span><o:p></o:p></p><p class=MsoNormal><span lang=EN-ZA style='font-size:10.0pt;font-family:"Arial","sans-serif";color:#1F497D'>PA: Nadia 021 959 4330</span><o:p></o:p></p></blockquote><p class=MsoNormal><o:p> </o:p></p></div><div style="position:absolute;margin:15px 0 0 0px; padding-top:10px;padding-right:15px;min-width:350px; border-top:1px solid #ccc;font-size:12px; color: #333; font-family:arial,'Hiragino Sans GB',Tahoma,Helvetica,STHeiti; ">This email has been protected by YAC (Yet Another Cleaner) <a href="http://www.yac.mx?source=email" style="display:block;padding-top:5px; color:#2bafed;text-decoration:none;">www.yac.mx</a></div></body></html>