[Stoves] Re Alexis Belonio article

[Simon and Zoe]

Crispin,

did you mean to state:

> b) the
> heat transfer ability of hot steam (being twice that of air)

I suspect you intended to write heat capacity(?). I would imagine the 'heat
transfer ability' of steam compared to air is probably less since for the
same amount of energy absorbed by the gas the increase in temperature will
be approximately half. So the flow of gas will be cooler than either air or
CO2, reducing the heat transfer.

Simon

----- Original Message -----
From: "Crispin Pemberton-Pigott" <crispinpigott at gmail.com>
To: "Stoves" <stoves at listserv.repp.org>
Cc: "Mike Spendlove" <mospendl at engmail.uwaterloo.ca>
Sent: Friday, April 06, 2007 1:47 AM
Subject: [Stoves] Re Alexis Belonio article


> Dear Andrew
>
> Last first:
>
> > A shorter flame also has less propensity to lose heat, through
> >radiation.
>
> That is what I have noted on the FSP stove experiemnts.  As I was able to
> get the mixing better and better over the course of a year, the flame
> shortened and got hotter, the CO dropped and I was able to get the excess
> air down to 100%.  In general I expect Alexis can get the same things, but
> he will have a materials problem right away because it is going to melt
> everything.
>
> Then:
>
> >[steam] seemed to interfere with the combustion of
> >wood. I may just have introduced too much steam
> >AND/OR there were still water droplets in the jet. With
> >every gramme of steam robbing 3KJ from the fire it can be very
> >significant.
>
> I want to look carefully at the possibility that some of this heat can be
> recycled.  I had a long talk about this today with Mike Spendlove from
> Engineers Without Borders from Waterloo University.  There is at least the
> possibility that heat picked up on the inside of the steam boiler, that is
> with a coiled superheating tube, could usefully be returned to the fire
> provided the overall effect was not to a) increase the volume of the gases
> to the point that heat is lost past the pot from high velocity, and b) the
> heat transfer ability of hot steam (being twice that of air) more than
> compensated for the heat lost creating the steam.
>
> We agreed it was likely the latent heat of evaporation would be lost for
> sure and that is a big tax on the system.  It may be that the main effect
is
> to raise the power output from any given stove at the cost of lower
> efficiency at higher power.  Smaller stove, bigger power....possibly
> interesting...
>
> We agreed that there was at least the possibility that having very dry
fuel
> mixed with a controlled amount of steam could produce a lower emission
level
> in a relatively choked fire, perhaps the EA at 25%, which means that one
> could reduce the excess air significantly while still maintaining the
clean
> burn.  This seems the most promising possibility, to me.
>
> The heat transfer enhancement might offer some gain to offset the ...shall
I
> call them 'steam losses'?  If the overall effect is to capture heat going
> through the stove body and run it back into the fire, then the combustion
> temperature is raised which in general lowers CO and hopefully PM 2.5's.
My
> inclination is to greatly limit the steam quantity admitted, superheat it
to
> a temperature above that of the exiting gases with an internal coil, and
> them limit the excess air until the emissions rise to the acceptable
limit.
> Such a stove might be surprisingly small for its power output.
>
> Regards
> Crispin
>
>
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