Dear Julien I think it is a mistake (or a poor assumption) to assume that a 'small char fire' is a) at the bottom, b) is not an effective heat source and c) represents a loss of some kind.
The distance between a heat source and a pot is not as indicative of anything significant. My rule is: Never Assume Anything. Calculate first, then observe, as appropriate. The simmering that is sometimes done in a cooking event is often well supplied with heat with a low power char fire at the end. Convective heat transfer can be very efficient. Basically the argument that distance matters is an assumption that most heat transfer from burning char is from radiant. This is nearly never true in a real fire. If the convective heat transfer is done with a low excess air level, it can be very good. Regards Crispin -----Original Message----- From: Stoves [mailto:[email protected]] On Behalf Of Julien Winter Sent: Friday, July 19, 2013 9:08 PM To: Discussion of biomass cooking stoves Subject: [Stoves] Comparing the fate of fuel energy between stoves -- a simple table? Hello Stovers; I am in Dhaka, Bangladesh, and I am going into a meeting in a couple of days to talk about biochar production through cookstoves. I have already been asked a question about whether biochar-making is a cost (in fuel) that stove-user may not want to make. For example, "why not burn the fuel to ash and not save the biochar?" ... to which I reply that for a ND-TLUD, 70% of the fuel energy was in the gas fire, and the carbon fire is a long way from the pot, and a TLUD is a great deal more efficient that a traditional stove, and who would want a high temperature carbon fire at the bottom of one's cherished stove anyway. I realize that there are some huge ceteris paribus assumptions to be made about standard conditions for comparing different stove types and fuels, but can anybody have a crack at filling in this "simple" table? I just want some ballpark figures to help justify biocharmakery. FATE OF THE ENERGY CONTAINED IN A WOOD FUEL STOVE_TYPE COOKING BIOCHAR LOST ============================================ ----------------------- (%) ----------------------------- 1) ND-TLUD 2) 3-stone 3) Anila 4) Chula 5) etc. I have just put in some stove names as examples. The value for %energy in biochar is zero for many stoves, so many comparisons amounts to a comparison of stove efficiencies. As must be the case for many less well off countries, the most ecologically sound method of making biochar in Bangladesh will be through their cookstoves, and the biggest, most immediate impact of biochar on people's lives will be to improve the fertility of homestead gardens. That is easy to say; it will be a lot harder to do. Thanks, Julien. -- Julien Winter Cobourg, ON, CANADA _______________________________________________ Stoves mailing list to Send a Message to the list, use the email address [email protected] 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/ _______________________________________________ Stoves mailing list to Send a Message to the list, use the email address [email protected] 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/
