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</o:shapelayout></xml><![endif]--></head><body 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 Ken<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'>You must be just dying to hook a Stirling engine to one of those things.<o:p></o:p></span></p><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><b><span lang=EN-US style='font-size:10.0pt;font-family:"Tahoma","sans-serif";color:#1F497D'>></span></b>Subsequently the flue has been lined with 1" of refractory - a partial solution <span style='color:#1F497D'>–</span> <span style='color:#1F497D'><o:p></o:p></span></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>And a conventional one. You will need to have a lining with very high thermal shock resistance. These little systems are far more challenging (material-wise) than industrial ones where everything stay hot for months at a time.<o:p></o:p></span></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='color:#1F497D'>…</span>but I like the idea of using an annular heat shield that provides accelerated cooling and air pre-heat.<o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>If you get enough heat pulled off the surface you can get a good lifetime out of your SS without going to really expensive materials. Remember that the outer shell will form an effective insulation around the hot shell so the air passing through needs to be known pretty well, and needed. <o:p></o:p></span></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>It is really worth modelling the heat flow in Excel. Pretty straight forward stuff. You may have to keep the hot wall thin in order to get its inside temperature down into the 600 C range just to be safe. Remember 3CR12 can operate up to 700 but its conduction is lousy (0.24). To do that you will have to have an preheated air temperature max probably 100 C below that, at least. I have seen 500 C air coming through such an arrangement so it is possible. The annular gap will set the volume and together with the flow rate the total heat you can pull off. See if you can balance that with the air demand, or the secondary air demand. Hence the suggestion for a spreadsheet. The Vesto is recycling maybe 15% of the combustion heat (max) through the preheater.<o:p></o:p></span></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>You may want to taper the preheater larger to give a lower velocity at the hot end to allow for a higher heat transfer efficiency as the </span><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Ä</span><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>T drops, putting the hottest air end at the coolest burner end. This is counter-intuitive compared with a hot water heat exchanger where the temperature of the internal surface does not enter into the equation. You have a different priority. You need to see what the internal temperature of the burner is above all, not the total preheating efficiency, in order to prevent condensation of the chrome in the alloy (pulling away from the oxidation sites).<o:p></o:p></span></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>You sure have a nice looking burner there! What is the O2 level at the exhaust?<o:p></o:p></span></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Regards<o:p></o:p></span></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Crispin<o:p></o:p></span></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><o:p> </o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>Ken <o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><o:p> </o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>Doing sustainable energy work in Northern California.<o:p></o:p></p></div></div></body></html>