Andrew CC list Thanks for the following. See few inserts below
----- Original Message ----- From: [email protected] To: "Discussion of biomass cooking stoves" <[email protected]> Sent: Sunday, March 11, 2012 5:19:58 AM Subject: Re: [Stoves] radiant heat capture, total heat measurement On Sat, 10 Mar 2012 18:58:43 +0000 (UTC), [email protected] wrote: >1. The last several paragraphs below are coming out more negatively on radiant >heat capture than I think are appropriate. Remember, the initial information >provided by Paul Olivier on March 2, when he said: > >"When a wire mesh dome is placed on top of the burner and burner housing, >this roughly doubles the amount of heat being transferred to a pot: " Please see my other post today. I cannot judge the power emitted by the radiant dome without an idea of its temperature and cross section subtended by the pot, even then my maths is rusty. Then we would also need the massflow and temperature after the dome and temperature above the pot. > >2. I think this doubling has little to do with the exchange below (and a few >earlier that are similar). Radiant heaters are widely sold because of their >efficiency in heat transfer - in many cases involving zero convection. Zero convection because there is zero mass flow? [RWL: I was thinking gas powered, with radiation downward and convection upard.] Electric radiant heaters being the prime example. Of course we can consider the possibilities of a gas fired radiant heater that uses staggered radiating elements, from cherry red down to black heat and discards the flue gas at a lowish (250c??) temperature that is comparable with a conventional convective heater with similar exhaust temperature but here we have one radiating element, the strainer/dome, at,guessing, ~1000C. [RWL: I don't think Paul's mesh is quite that high. I think maybe closer to 70 oC. At this site: http://dwb4.unl.edu/chemistry/dochem/DoChem007.html there is this set of colors for a nichrome wire no light < 500 °C not quite red 500-550 °C dark red 650-750 °C bright red 850-950 °C yellowish red 1050-1150 °C not quite white 1250-1350 °C white > 1450 °C >Given we have only one (above) piece of data for one stove, the chances are >that a doubling is not the maximum we can achieve. > >3. I would look at this as a conservation of energy problem. We know that we >can transfer more energy to the pot if the radiator is hotter. There may be >catalysts that we can employ. We know how to use reflectors and obtain high >absorption (and sometimes simultaneously low emissivity ) >In my reading on ceramic foam, I found that some foam is being employed so as >to have gas combustion take place inside the foam!. We used a catalytic ("flameless") burner on the little recirculating wood dryer I demonstrated to you many years ago. Yes I do like the idea of the combustion taking place within the ceramic foam, it allows micro mixing (Turbulence), high Temperature as there are few heat losses in the tiny spaces and long dwell Time as the gases find their way out. [RWL: I didn't remember that, but hope you can suggest some sources for a similar capability. Thanks for the added information. Ron AJH _______________________________________________ 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://www.bioenergylists.org/
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