<html><head><meta http-equiv="Content-Type" content="text/html charset=windows-1252"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;"><div>Crispin and list:</div><div><br></div><div> Thanks for the updated cite. Makes at least two that are not behind paywalls. Hope we can find some that are even more current and easy obtainable. But there is a big literature on heat pipes outside the cooking arena.</div><div><br></div><div><span class="Apple-tab-span" style="white-space:pre"> </span>I think we can learn a lot from the solar cooker side - but my interest is on biomass stoves and the ability to feed multiple pots from a single flame. You talk also about thermo-siphoning and pumps. I am describing neither of those - a heat pipe operates on a very different principle as I know you know.</div><div><br></div><div><span class="Apple-tab-span" style="white-space:pre"> </span>The word “diode” is important here.</div><div><br></div><div><span class="Apple-tab-span" style="white-space:pre"> </span>I talked with one of the last references in your cite - Mr. C J Swet at about the time he wrote that 1974 article - on (I recall) a thermo siphon principle.</div><div><br></div><div>Ron</div><div><br></div><br><div><div>On Jan 29, 2014, at 12:13 PM, Crispin Pemberton-Pigott <<a href="mailto:crispinpigott@gmail.com">crispinpigott@gmail.com</a>> wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><div lang="EN-CA" link="blue" vlink="purple" style="font-family: Helvetica; font-size: 18px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><div class="WordSection1" style="page: WordSection1;"><div style="margin: 0mm 0mm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;"><span style="font-size: 11pt; font-family: Calibri, sans-serif; color: rgb(31, 73, 125);">Dear Ron<o:p></o:p></span></div><div style="margin: 0mm 0mm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;"><span style="font-size: 11pt; font-family: Calibri, sans-serif; color: rgb(31, 73, 125);"> </span></div><div style="margin: 0mm 0mm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;"><span style="font-size: 11pt; font-family: Calibri, sans-serif; color: rgb(31, 73, 125);">Good find.<o:p></o:p></span></div><div style="margin: 0mm 0mm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;"><span style="font-size: 11pt; font-family: Calibri, sans-serif; color: rgb(31, 73, 125);"> </span></div><div style="margin: 0mm 0mm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;"><span style="font-size: 11pt; font-family: Calibri, sans-serif; color: rgb(31, 73, 125);">This is basically identical to a system built by Mercedes in Germany that was shopped to South Africa for testing. It cost an absolute fortune so there was no plan to make a commercial version at that stage. I understand it had been fabricated by the apprentices working at Mercedes as a development project for high solar insolation countries.<o:p></o:p></span></div><div style="margin: 0mm 0mm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;"><span style="font-size: 11pt; font-family: Calibri, sans-serif; color: rgb(31, 73, 125);"> </span></div><div style="margin: 0mm 0mm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;"><span style="font-size: 11pt; font-family: Calibri, sans-serif; color: rgb(31, 73, 125);">There is a paper Stumpf, P., Balzar, A., Eisenmann, W., Wendt, S., Ackermann, H., Vajen, K., 2001. Comparative measurements and theoretical modelling of single- and double-stage heat pipe coupled solar cooking systems for high temperatures. Solar Energy 71 (1), 1<span lang="EN-US">–</span>10, that might be relevant (it is cited at the end). I am wondering if there is a connection between Mercedes and those guys. Just a thought.<o:p></o:p></span></div><div style="margin: 0mm 0mm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;"><span style="font-size: 11pt; font-family: Calibri, sans-serif; color: rgb(31, 73, 125);"> </span></div><div style="margin: 0mm 0mm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;"><span style="font-size: 11pt; font-family: Calibri, sans-serif; color: rgb(31, 73, 125);">So eventually this pair (was it three?) devices made its way in not very perfect condition to St Joseph’s Missions east of Manzini, Swaziland and I was called in to see if I could get it working. The working fluid was peanut oil which has the highest practical operating temperature, they said. I think marula oil is higher but you can check.<o:p></o:p></span></div><div style="margin: 0mm 0mm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;"><span style="font-size: 11pt; font-family: Calibri, sans-serif; color: rgb(31, 73, 125);"> </span></div><div style="margin: 0mm 0mm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;"><span style="font-size: 11pt; font-family: Calibri, sans-serif; color: rgb(31, 73, 125);">The construction was identical to that linked above. Each unit was quite large. There were two cooking areas which were really stainless steel bowls that were sunken below the liftable, reasonably insulated wooden lid.<o:p></o:p></span></div><div style="margin: 0mm 0mm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;"><span style="font-size: 11pt; font-family: Calibri, sans-serif; color: rgb(31, 73, 125);"> </span></div><div style="margin: 0mm 0mm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;"><span style="font-size: 11pt; font-family: Calibri, sans-serif; color: rgb(31, 73, 125);">There were connector problems (the collectors are separable) and that was easy to fix. The problem, according to the cooks, is that they did not cook properly. They were good at heating water but not good at ‘cooking’. I traced the problem eventually to the fact that the thermosiphon system that circulated hot oil from the reservoir to the cooking pot was circulating too slowly. It was hot enough, but it was short of power, meaning the flow rate of the oil could not be increased to the point that a pot would ‘look like it is cooking’ even though the oil temperature was above 150 C. That was disappointing and systemic.<o:p></o:p></span></div><div style="margin: 0mm 0mm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;"><span style="font-size: 11pt; font-family: Calibri, sans-serif; color: rgb(31, 73, 125);"> </span></div><div style="margin: 0mm 0mm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;"><span style="font-size: 11pt; font-family: Calibri, sans-serif; color: rgb(31, 73, 125);">We had email correspondence in those days with the factory and some comments were traded back and forth about what to do. Having been given the final verdict that the problem was the heat transfer rate being limited by the piping restricting the flow rate between the reservoir and the pots directly above it, and the lack of a circulation pump of any kind to increase it, the reply came that the real problem was the connections between the panels and the cooking unit. In other words they blamed me for their design errors.<o:p></o:p></span></div><div style="margin: 0mm 0mm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;"><span style="font-size: 11pt; font-family: Calibri, sans-serif; color: rgb(31, 73, 125);"> </span></div><div style="margin: 0mm 0mm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;"><span style="font-size: 11pt; font-family: Calibri, sans-serif; color: rgb(31, 73, 125);">The thing definitely collected a lot of heat and stored it. Anyone wanting to build one should pay close attention to the heat transfer rate (in Watts) between the heat store and the cooking vessel. It is a good example of the difference between temperature and a quantity of heating.<o:p></o:p></span></div><div style="margin: 0mm 0mm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;"><span style="font-size: 11pt; font-family: Calibri, sans-serif; color: rgb(31, 73, 125);"> </span></div><div style="margin: 0mm 0mm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;"><span style="font-size: 11pt; font-family: Calibri, sans-serif; color: rgb(31, 73, 125);">Peanut oil is a good heat transfer and storage medium. The thermosiphon method is good for getting heat into the system.<o:p></o:p></span></div><div style="margin: 0mm 0mm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;"><span style="font-size: 11pt; font-family: Calibri, sans-serif; color: rgb(31, 73, 125);"> </span></div><div style="margin: 0mm 0mm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;"><span style="font-size: 11pt; font-family: Calibri, sans-serif; color: rgb(31, 73, 125);">Remember everyone, that Prof Bernhard Scheffler (Solar Energy Society of South Africa) proved mathematically in 1982 that you get the maximum heat gain per day by passing the volume of the working fluid through the collector exactly once during the solar heating period, say, 8 hours. That fixes lots of design parameters.<o:p></o:p></span></div><div style="margin: 0mm 0mm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;"><span style="font-size: 11pt; font-family: Calibri, sans-serif; color: rgb(31, 73, 125);"> </span></div><div style="margin: 0mm 0mm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;"><span style="font-size: 11pt; font-family: Calibri, sans-serif; color: rgb(31, 73, 125);">Regards<o:p></o:p></span></div><div style="margin: 0mm 0mm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;"><span style="font-size: 11pt; font-family: Calibri, sans-serif; color: rgb(31, 73, 125);">Crispin<o:p></o:p></span></div><div style="margin: 0mm 0mm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;"><span style="font-size: 11pt; font-family: Calibri, sans-serif; color: rgb(31, 73, 125);"> </span></div><div style="margin: 0mm 0mm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;"><span style="font-size: 11pt; font-family: Calibri, sans-serif; color: rgb(31, 73, 125);"> </span></div><div><div style="margin: 0mm 0mm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;">Tom: cc List, Crispin (new thread name)<o:p></o:p></div></div><div><div style="margin: 0mm 0mm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;"><o:p> </o:p></div></div><div><div style="margin: 0mm 0mm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;"> <span class="apple-tab-span"> <span class="Apple-converted-space"> </span></span>The number one new thought I want to emphasize from my brief report is that of the heat pipe/thermal diode - which I have not seen mentioned on this list. Googling found this (no fee) paper on solar cookers that is relevant:<o:p></o:p></div></div><div><div style="margin: 0mm 0mm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;"><o:p> </o:p></div></div><div><div style="margin: 0mm 0mm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;"> <a href="http://cfc.kscia.or.kr/new/wwwboard/admin/wwwboard/attach/1087363006/26.pdf" style="color: purple; text-decoration: underline;">http://cfc.kscia.or.kr/new/wwwboard/admin/wwwboard/attach/1087363006/26.pdf</a><o:p></o:p></div></div><div><div style="margin: 0mm 0mm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;"><o:p> </o:p></div></div><div><div style="margin: 0mm 0mm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;"><span class="apple-tab-span"> <span class="Apple-converted-space"> </span></span>Several other references to cooking, but this the only no-fee paper in the first ten Google pages for the search I used (with “stove”).<o:p></o:p></div></div><div><div style="margin: 0mm 0mm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;"><o:p> </o:p></div></div><div><div style="margin: 0mm 0mm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;"><o:p> </o:p></div></div><div><div style="margin: 0mm 0mm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;"> <span class="apple-tab-span"> <span class="Apple-converted-space"> </span></span>This is to ask if anyone has been trying this out with biomass cook stoves. What working "fluid" is appropriate (maybe lead)? A high temperature oil? Note this could also be very appropriate for ovens, where we mostly want no smoke.<o:p></o:p></div></div><div><div style="margin: 0mm 0mm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;"><o:p> </o:p></div></div><div><div style="margin: 0mm 0mm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;"><span class="apple-tab-span"> <span class="Apple-converted-space"> </span></span>One cook stove could feed several ovens (or any cooking surface). Eliminates the soot problem, also. We could totally insulate the cook pot while cooking.<o:p></o:p></div></div><div><div style="margin: 0mm 0mm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;"><o:p> </o:p></div></div><div><div style="margin: 0mm 0mm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;"><span class="apple-tab-span"> <span class="Apple-converted-space"> </span></span>This could be relatively low cost - just a closed pipe. Nothing to wear out.<o:p></o:p></div></div><div><div style="margin: 0mm 0mm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;"><o:p> </o:p></div></div><div><div style="margin: 0mm 0mm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;"> <span class="apple-tab-span"> <span class="Apple-converted-space"> </span></span>This did not come up at ETHOS. Anyone needing the 3-pager report noted below can get from the stoves archives or write me.<o:p></o:p></div></div><div><div style="margin: 0mm 0mm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;"><o:p> </o:p></div></div><div><div style="margin: 0mm 0mm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;">Ron<o:p></o:p></div></div><div><div style="margin: 0mm 0mm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;"><o:p> </o:p></div></div><div><div style="margin: 0mm 0mm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;"><o:p> </o:p></div></div></div>_______________________________________________<br>Stoves mailing list<br><br>to Send a Message to the list, use the email address<br><a href="mailto:stoves@lists.bioenergylists.org">stoves@lists.bioenergylists.org</a><br><br>to UNSUBSCRIBE or Change your List Settings use the web page<br>http://lists.bioenergylists.org/mailman/listinfo/stoves_lists.bioenergylists.org<br><br>for more Biomass Cooking Stoves, News and Information see our web site:<br>http://stoves.bioenergylists.org/</div></blockquote></div><br></body></html>