<html><head><style type='text/css'>p { margin: 0; }</style></head><body><div style='font-family: Arial; font-size: 12pt; color: #000000'>Andrew CC list<br><br> Thanks for the following. See few inserts below<br><br><hr id="zwchr"><b>From: </b>ajheggie@gmail.com<br><b>To: </b>"Discussion of biomass cooking stoves" <stoves@lists.bioenergylists.org><br><b>Sent: </b>Sunday, March 11, 2012 5:19:58 AM<br><b>Subject: </b>Re: [Stoves] radiant heat capture, total heat measurement<br><br>On Sat, 10 Mar 2012 18:58:43 +0000 (UTC), rongretlarson@comcast.net<br>wrote:<br><br>>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: <br>><br>>"When a wire mesh dome is placed on top of the burner and burner housing, <br>>this roughly doubles the amount of heat being transferred to a pot: " <br><br>Please see my other post today. I cannot judge the power emitted by<br>the radiant dome without an idea of its temperature and cross section<br>subtended by the pot, even then my maths is rusty. Then we would also<br>need the massflow and temperature after the dome and temperature above<br>the pot.<br>><br>>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. <br><br>Zero convection because there is zero mass flow?<strong>[RWL: I was thinking gas powered, with radiation downward and convection upard.]</strong><br> <br> Electric radiant<br>heaters being the prime example. Of course we can consider the<br>possibilities of a gas fired radiant heater that uses staggered<br>radiating elements, from cherry red down to black heat and discards<br>the flue gas at a lowish (250c??) temperature that is comparable with<br>a conventional convective heater with similar exhaust temperature but<br>here we have one radiating element, the strainer/dome, at,guessing,<br>~1000C.<br><br><span style="font-weight: bold;">[RWL: I don't think Paul's mesh is quite that high. I think maybe closer to 70 oC. At this site:<br><br>http://dwb4.unl.edu/chemistry/dochem/DoChem007.html<br><br> there is this set of colors for a nichrome wire<br></span><br><table border="4" cellpadding="0" cellspacing="2" width="242"><tbody><tr><td width="110">no light</td>
<td width="112">< 500 °C</td>
</tr>
<tr>
<td width="110">not quite red</td>
<td width="112">500-550 °C</td>
</tr>
<tr>
<td width="110">dark red</td>
<td width="112">650-750 °C</td>
</tr>
<tr>
<td width="110">bright red</td>
<td width="112">850-950 °C</td>
</tr>
<tr>
<td width="110">yellowish red</td>
<td width="112">1050-1150 °C</td>
</tr>
<tr>
<td width="110">not quite white</td>
<td width="112">1250-1350 °C</td>
</tr>
<tr>
<td width="110">white</td>
<td width="112">> 1450 °C</td></tr></tbody></table><br><br><br>>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. <br>><br>>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 ) <br>>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!. <br><br>We used a catalytic ("flameless") burner on the little recirculating<br>wood dryer I demonstrated to you many years ago. Yes I do like the<br>idea of the combustion taking place within the ceramic foam, it allows<br>micro mixing (Turbulence), high Temperature as there are few heat<br>losses in the tiny spaces and long dwell Time as the gases find their<br>way out.<br><br> <span style="font-weight: bold;">[RWL: I didn't remember that, but hope you can suggest some sources for a similar capability.<br> Thanks for the added information. Ron<br></span><br>AJH<br><br>_______________________________________________<br>Stoves mailing list<br><br>to Send a Message to the list, use the email address<br>stoves@lists.bioenergylists.org<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://www.bioenergylists.org/<br><br></div></body></html>