[Stoves] Annular Crosscurrent Burner for ND-TLUD

[Julien Winter]

Hi Stovers;

I think that I backed down too quickly on criticism over the way I used my
thermocouples.  The measurements I made are doing the job that I intended
them to do.  The problem may be that I didn't make my intensions clear
enough.  One of the reasons I use the Power Point format, is that I can
present information graphically, quickly, but it is rather verbally terse.

Something that I took out of an earlier version of my write-up was that
temperature is an intensive property, and heat is an extensive
property.  Temperature doesn't depend on the amount of substance being
measured.  Heat is proportional to the amount of substance.  We can measure
the flux of heat, but there is no such thing as a flux of temperature.
However, the flow of heat causes changes in the temperature of the
substances through which it moves, such as thermocouples.

What I was not trying to do in my experiment was equate temperature with
actual heat flux.  I was just using them as an indirect indicator of the
amount of heat experienced by the bottom of a pot.  That more or less is a
reflection of the efficiency of a burner to transfer energy from gasified
fuel to pot.

Simply put: poor energy transfer —> cold thermocouples == cold pot.
                   (theoretical cause)          (measured)
   (predicted)

Factors affecting energy transfer such as dilution by excess secondary air,
radiant / convective heat, and flame temperature are interesting theories,
but unmeasured, hence speculation.

If the thermocouples in Annular Burner (AB) were cold relative to
Peripheral Burner (PB) at the same gasification rate, then there would have
been a problem for the AB concept.  A pot above an AB would likely be
colder than a pot above a PB.   The AB would have to be abandoned, or
modified.

Since I didn't find much difference in thermocouple temperature between AB
and PB, I am optimistic that the AB concept will be OK, because I don't
yet have a reason to reject the null hypothesis that energy transfer in AB
and PM are not substantively different.

These preliminary observations show that the AB is viable (or more
precisely, that is in not unviable).  Now, we are justified to go into more
detail.  We need to experiment with the architecture of the AB, and measure
its effect on combustion efficiency and gas emissions.  We will need to
make direct measurement of heat transfer.



However, the thermocouples found a problem.  They tells us that the
next tasks are not going to be so simple.

A very important finding of this study is that riser temperature decreases
over time at high gasification rates.   Riser temperature showed a clear
interaction between gasification rate and duration of burn; and
it occurred with both burners.

The interaction between gasification rate and time needs to part of
characterizing natural draft, top-lit updraft gasifiers (ND-TLUD) and their
burners for gas and soot emissions, and the actual rate of energy transfer
from fuel to pot.   We should also know the superficial velocity of primary
air, and secondary air, if it can't be calculated.

It is because of this interaction that I think that the tests at various
grate apertures are more appropriate for a ND-TLUD in to determining the
turndown, efficiency, and emissions, than a single "Water Boiling Test."
It is a lot more work, but I think it is necessary for any mass-produced
ND-TLUD.


Cheers,
Julien.












-- 
Julien Winter
Cobourg, ON, CANADA
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