[Stoves] radiant heat capture, total heat measurement

[rongretlarson at comcast.net]

Andrew CC list 

Thanks for the following. See few inserts below 

----- Original Message -----
From: ajheggie at gmail.com 
To: "Discussion of biomass cooking stoves" <stoves at lists.bioenergylists.org> 
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), rongretlarson at comcast.net 
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 
stoves at 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://www.bioenergylists.org/ 

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.bioenergylists.org/pipermail/stoves_lists.bioenergylists.org/attachments/20120312/63fb70a1/attachment.html>