[Stoves] Radiation Analysis for Gasifier

[Marc Pare]

Hi all,

First a short story, then a presentation of some analysis I've been working
on the last week (with the help of Crispin and Matt Redmond). You can skip
the story, if you like.

*the story*
My friend Isaac from Tech tells of his most traumatic experience training
to be an engineer: "We were giving a presentation on a design of a hybrid
vehicle. The professor asks us why we choose one particular motor over
another. 'Oh, it was bigger, so we figured it would be better.' The
professor stopped them there. Stood up, turned to the class, and yelled:
"ENGINEERS QUANTIFY!"

*the results*
In the spirit of Isaac's legendary professor, I sought to provide some
clarity to the speculation of radiative heat transfer and improved cook
stoves by doing some simple analysis.

The setup was simple: what is the theoretical upper bound on contribution
to heat transfer by the "dome-shaped emitter" described over the last week.

It turns out that *the dome-shaped emitter has negligible impact on the
heat transfer*. Further testing supported this conclusion, but I figured it
was worth showing how we were able to show with theory that the dome-shaped
thing was not important.

The results place the upper bound on power from the emitter at *0.301 kW *vs.
the power required to boil water at *1.65 kW*.
This means that even at 100% efficiency, the emitter will only improve your
thermal performance by about 20%. (not the reported 100% improvement)

I attached a pdf explaining the theory and a spreadsheet of the
calculation. You can also get them here:
http://notwandering.com/radiation.php

*thanks*
Matt Redmond for a first pass on the spreadsheet
Crispin for quadruple-checking the spreadsheet and adding improved water
boiling numbers


feedback is welcome. there is always the chance that there are mistakes!

Best,

Marc Paré
B.S. Mechanical Engineering
Georgia Institute of Technology | Université de Technologie de Compiègne

my cv, etc. | http://notwandering.com


On Sat, Mar 17, 2012 at 2:05 PM, Crispin Pemberton-Pigott <
crispinpigott at gmail.com> wrote:

> Great!****
>
> ** **
>
> Marc you are doing us a great service. Simply by collecting the little
> spreadsheets circulated here, one can gain a good education in stove design.
> ****
>
> ** **
>
> The volunteer’s efforts are always rewarded.****
>
> ** **
>
> Many thanks****
>
> Crispin****
>
> ** **
>
> +++++++****
>
> # I appeal to Marc not to hide his light under a bushel. These discussion
> also need numbers and methods so the reality of things becomes widespread.
> ****
>
>
> Write-up is coming :)****
>
> Putting in some effort so that it's a useful resource for folks in the
> future.****
>
> Marc Paré
> B.S. Mechanical Engineering
> Georgia Institute of Technology | Université de Technologie de Compiègne
>
> my cv, etc. | http://notwandering.com
>
> ****
>
> On Sat, Mar 17, 2012 at 1:55 PM, Crispin Pemberton-Pigott <
> crispinpigott at gmail.com> wrote:****
>
> Dear Alexis and Paul****
>
>  ****
>
> Thanks so much for the very open discussion and open design of the
> burners. Alexis, when we met in Thailand you mentioned that you have
> switched to a premixed flame and if you recall we did talk a bit about the
> top end of the version of the stove you demonstrated.****
>
>  ****
>
> Is it correct that you are now using a premixed flame? I have been in
> extensive conversation with Paul O about the burner for some time and it
> seems at present to be a blend of premixing with secondary air and as Paul
> says, some tertiary air for the final burnout.****
>
>  ****
>
> The difference in performance that Paul mentioned and which got some much
> discussion going about heat transfer from the hot dome could have at least
> three quite different origins and there is a lot of merit in tracking down
> the difference. The first might be that the structure under the pot on
> Paul’s present configuration is much more closed than the one I saw in
> Thailand. That could account for all the difference in the boiling time. A
> second possibility is the reduction in excess air either through the burner
> where flames are present or between the flames and the final departure of
> the pot and stove structure, by which I mean the outer ring. Until the hot
> gases leave the pot and vent into the room, the air present in that gas
> stream is technically part of the combustor. If there is a lot of cold air
> entering the region under the pot, then it is counted as excess air in the
> heat exchanger.****
>
>  ****
>
> Paul, thanks for putting the pictures of the development work you are
> doing. It is helpful for those who would like to work on stoves with
> minimal equipment to see how things work and what has been tried. It saves
> a lot of reinventing.****
>
>  ****
>
> With regard to the heat transfer from a radiant dome, Marc has been doing
> some calculations which I hope he will post here when he is confident in
> the method. That should settle the question as to whether or not a large
> increase in performance can be obtained by changing hot, relatively non-IR
> radiant gas into IR emitted from a wide gauze surface.****
>
>  ****
>
> It is well worth remembering that because a flame is pale blue in the
> visible range, that does not tell us what it is emitting in the IR which is
> invisible to human eyes. Looking through a translucent flame is not really
> a measure of emissions of heat. If you point an IR gun at a flame it will
> register a high temperature, even if it is as inaccurate as an unshielded
> thermocouple.****
>
>  ****
>
> I agree with the others that the discussion about heat transfer has been a
> good exploration of the subject. I appeal to Marc not to hide his light
> under a bushel. These discussion also need numbers and methods so the
> reality of things becomes widespread.****
>
>  ****
>
> Regards****
>
> Crispin****
>
>
>
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