Crispin and list: 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.
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. The word “diode” is important here. 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. Ron On Jan 29, 2014, at 12:13 PM, Crispin Pemberton-Pigott <crispinpig...@gmail.com> wrote: > Dear Ron > > Good find. > > 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. > > 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), 1–10, 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. > > 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. > > 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. > > 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. > > 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. > > 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. > > Peanut oil is a good heat transfer and storage medium. The thermosiphon > method is good for getting heat into the system. > > 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. > > Regards > Crispin > > > Tom: cc List, Crispin (new thread name) > > 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: > > > http://cfc.kscia.or.kr/new/wwwboard/admin/wwwboard/attach/1087363006/26.pdf > > 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”). > > > 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. > > 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. > > This could be relatively low cost - just a closed pipe. Nothing > to wear out. > > This did not come up at ETHOS. Anyone needing the 3-pager > report noted below can get from the stoves archives or write me. > > Ron > > > _______________________________________________ > Stoves mailing list > > to Send a Message to the list, use the email address > stoves@lists.bioenergylists.org > > to UNSUBSCRIBE or Change your List Settings use the web page > http://lists.bioenergylists.org/mailman/listinfo/stoves_lists.bioenergylists.org > > for more Biomass Cooking Stoves, News and Information see our web site: > http://stoves.bioenergylists.org/
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