[Stoves] radiant heat capture, total heat measurement

[Paul Olivier]

See comments.

On Sun, Mar 11, 2012 at 6:19 PM, <ajheggie at gmail.com> wrote:

> On Sun, 11 Mar 2012 07:30:24 +0700, Paul Olivier wrote:
>
> >>
> >
> >It is impossible to light the burner with the strainer in place.
> >So in lighting a burner, I have to run it for a short while without the
> >strainer.
> >And when I put the strainer on the burner, I always have to turn down the
> >fan.
>
> Does the fan simultaneously supply primary air ( for the gasifier) and
> the secondary air to burn the offgas?


The fan only supplies primary air.
Secondary air is drawn in between the burner housing and the burner.
Some secondary air also come in through the dome.


> You mention the initial flame
> pyrolysis/gasification in the primary chamber migrates to the burner
> holes after some time.
>

At a normal fan speed, most of the gas is burned at the burner holes.
The gases that comprise the diffusion tail are burned within the dome.


> >
> >To get full and uniform ignition at all burner holes without the strainer,
> >a certain fan speed is required.
> >But to get full and uniform ignition at all burner holes with the
> strainer,
> >a lesser fan speed is required.
>
> Difficult to judge without seeing things but my guess this is to do
> with air:fuel mixture rather than flame speeds. Initially the burn in
> the primary chamber using more air than necessary for gasification
> (secondary burn happening to some extent in the primary chamber}.
>
> >With the strainer the flames are far more consistent and stable.
> >The flames acquire structure and are not easily influenced by the wind.
> >This gives me reason to believe that the transfer of convective heat is
> >much more efficient when a dome is present.
> >So with a more efficient transfer of heat by convective means
> > and with the whole new dimension of thermal radiation that comes into
> play,
> > a lot more heat makes it into the pot.
>
> We'd need comparative (i.e. they don't need to be exact, given the
> problems with thermocouples in a gas stream) temperature readings both
> above and below the dome and in the same positions with the dome
> removed.
>

Yes, this needs to be done.


>
> I can see the strainer/dome acting as a means of shielding, mixing and
> providing turbulence.
>

The dome definitely shields.
It allows for an input of additional secondary air.
I do not think that it provides turbulence.


>
> I can't see what effect it would have in changing the flue gas
> characteristic to change the way the gases reaching the pot are
> transferred to it. The fact that you lower the fan rate when the dome
> is in position makes me think that with the fan dome you supply less
> excess air, this increases the flue gas temperature and thus the delta
> T twixt flue gas and pot increases heat transfer.
>

More primary air means more gas.
It does not necessarily mean more excess or secondary air.
My simple understanding of what is happening here is that
 wind does not disturb what is happening within the dome.
Wind does not dissipate heat so easily.
This gives a better transfer of convective heat,
 and it also gives more thermal radiation.


> AJH
>
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-- 
Paul A. Olivier PhD
27C Pham Hong Thai Street
Dalat
Vietnam

Louisiana telephone: 1-337-447-4124 (rings Vietnam)
Mobile: 090-694-1573 (in Vietnam)
Skype address: Xpolivier
http://www.esrla.com/
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