[Stoves] Radiation Analysis for Gasifier

[Alex English]

Marc,
Would you care to  take the next step and calculate what happens to gas 
temperature and convective heat transfer with the dome?
Just a thought........experiment.

Thanks for shedding light with your radiant contribution.
Alex

On 17/03/2012 8:30 AM, Marc Pare wrote:
> 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 <mailto: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 <mailto: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
>
>
>
> _______________________________________________
> 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/20120317/1e26a163/attachment.html>