[Stoves] Improving Thermal Efficiency (TARP-VE)

[Dean Still]

Dear Crispin,

How are you measuring PM in your experiments these days: light scattering,
pump and filter, or something else?

Best,

Dean

On Sun, Jun 3, 2012 at 3:18 PM, Crispin Pemberton-Pigott <
crispinpigott at gmail.com> wrote:

> Dear Ken****
>
> ** **
>
> You must be just dying to hook a Stirling engine to one of those things.**
> **
>
> *>*Subsequently the flue has been lined with 1" of refractory - a partial
> solution - ****
>
> And a conventional one. You will need to have a lining with very high
> thermal shock resistance. These little systems are far more challenging
> (material-wise) than industrial ones where everything stay hot for months
> at a time.****
>
> ...but I like the idea of using an annular heat shield that provides
> accelerated cooling and air pre-heat.****
>
> If you get enough heat pulled off the surface you can get a good lifetime
> out of your SS without going to really expensive materials. Remember that
> the outer shell will form an effective insulation around the hot shell so
> the air passing through needs to be known pretty well, and needed. ****
>
> It is really worth modelling the heat flow in Excel. Pretty straight
> forward stuff. You may have to keep the hot wall thin in order to get its
> inside temperature down into the 600 C range just to be safe. Remember
> 3CR12 can operate up to 700 but its conduction is lousy (0.24).  To do that
> you will have to have an preheated air temperature max probably 100 C below
> that, at least. I have seen 500 C air coming through such an arrangement so
> it is possible. The annular gap will set the volume and together with the
> flow rate the total heat you can pull off. See if you can balance that with
> the air demand, or the secondary air demand. Hence the suggestion for a
> spreadsheet. The Vesto is recycling maybe 15% of the combustion heat (max)
> through the preheater.****
>
> You may want to taper the preheater larger to give a lower velocity at the
> hot end to allow for a higher heat transfer efficiency as the ΔT drops,
> putting the hottest air end at the coolest burner end. This is
> counter-intuitive compared with a hot water heat exchanger where the
> temperature of the internal surface does not enter into the equation. You
> have a different priority.  You need to see what the internal temperature
> of the burner is above all, not the total preheating efficiency, in order
> to prevent condensation of the chrome in the alloy (pulling away from the
> oxidation sites).****
>
> You sure have a nice looking burner there! What is the O2 level at the
> exhaust?****
>
> Regards****
>
> Crispin****
>
> ** **
>
> Ken ****
>
> ** **
>
> Doing sustainable energy work in Northern California.****
>
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