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<p class="MsoNormal"><b><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Dear Ron, see replies below.<o:p></o:p></span></b></p>
<p class="MsoNormal"><b><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Jaakko<o:p></o:p></span></b></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span lang="EN-US" style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">From:</span></b><span lang="EN-US" style="font-size:10.0pt;font-family:"Tahoma","sans-serif""> Ronal W. Larson [</span><a href="mailto:rongretlarson@comcast.net"><span lang="EN-US" style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">mailto:rongretlarson@comcast.net</span></a><span lang="EN-US" style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">]
<br>
<b>Sent:</b> 19. elokuuta 2014 0:32<br>
<b>To:</b> Discussion of biomass; Saastamoinen Jaakko<br>
<b>Cc:</b> </span><a href="mailto:mika.horttanainen@lut.fi"><span lang="EN-US" style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">mika.horttanainen@lut.fi</span></a><span lang="EN-US" style="font-size:10.0pt;font-family:"Tahoma","sans-serif""><br>
<b>Subject:</b> Re: [Stoves] Request for help on TLUD operating data<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-GB">Jaakko cc List<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span class="apple-tab-span"><span lang="EN-GB">
</span></span><span lang="EN-GB">This is hugely helpful. Thanks.<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span class="apple-tab-span"><span lang="EN-GB">
</span></span><span lang="EN-GB">Yours below here is the third from you today - but the other two are easier to respond to, so I am starting here and do those next.<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span class="apple-tab-span"><span lang="EN-GB">
</span></span><span lang="EN-GB">See inserts below.<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-GB">On Aug 18, 2014, at 10:06 AM, Saastamoinen Jaakko <</span><a href="mailto:Jaakko.Saastamoinen@vtt.fi"><span lang="EN-GB">Jaakko.Saastamoinen@vtt.fi</span></a><span lang="EN-GB">> wrote:<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Dear Ron,</span><span lang="EN-GB"><o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"> </span><span lang="EN-GB"><o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">my previous postings considered forced primary air condition. The air rate was kept constant with a fan. The velocity of the ignition front depends
on the primary air rate also in the case of natural draught, but then the air rate is not given and it does not remain constant but depends on the balance equation</span><span lang="EN-GB"><o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"> </span><span lang="EN-GB"><o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">draught = pressure losses (including inlet to the device, fuel bed and outlet)</span><span lang="EN-GB"><o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span class="apple-tab-span"><span lang="EN-GB">
</span></span><span lang="EN-GB">[RWL1: I believe there is another reason for draught, that I hope you will comment on. When the main pyrolysis gases CO and H2 react with secondary air just above the hot char bed, there is a reduction of the number of particles
since<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span class="apple-tab-span"><span lang="EN-GB">
</span></span><span lang="EN-GB">2 CO + O2 = 2 CO2<o:p></o:p></span></p>
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<p class="MsoNormal"><span class="apple-tab-span"><span lang="EN-GB">
</span></span><span lang="EN-GB">2 H2 + O2 = 2 H2O <o:p></o:p></span></p>
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</span></span><span lang="EN-GB"><o:p></o:p></span></p>
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<p class="MsoNormal"><span class="apple-tab-span"><span lang="EN-GB">
</span></span><span lang="EN-GB">In both cases 3 particles before the combustion (left side) turn into 2 particles after (right side) - with a consequent lowering of pressure, encouraging both primary and secondary air flows. Of course, reduced by the presence
of Nitrogen in both the primary and secondary air streams, but bolstered by significant non-nitrogen gas release at the pyrolysis front. Is there a well-known “Law” to help put this additional helpful pressure drop into perspective? Note this doesn’t happen
with a methane flame where we have:<span class="apple-tab-span"> </span><o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span class="apple-tab-span"><span lang="EN-GB">
</span></span><span lang="EN-GB">CH4 +2 O2 = CO2 + 2 H2O (3 particles on each side of the equation)<o:p></o:p></span></p>
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<p class="MsoNormal"><b><span lang="EN-GB" style="color:#1F497D">Jaakko: The equation above states that draught is consumed in pressure losses. The draught is due to weight differences of gas columns due to density differences explained (below for the chimney),
which is the partly the same things as you explain above. The density difference is mainly caused by temperature difference. Gas density is proportional to 1/T, where T is in degrees of Kelvin, so the high temperature gas above the ignition from is much lighter
than the gas outside the cooker and causes the draught. </span></b><b><span lang="EN-GB"><o:p></o:p></span></b></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"> </span><span lang="EN-GB"><o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">A similar situation is when one heats a home with a stove. I have district heating but use sometimes also a masonry stove. The draught = gravity
* chimney height * density difference. The density difference =density of air outdoors minus density of air (averagely )in the chimney. When one ignites the wood logs in a stove, the draught is initially quite low, because the chimney is cool. One can increase
the draught by burning some paper in the chimney. One can decrease the pressure loss by opening the damper of the stove and the windows of the building. Then after some time the chimney gets hotter and draught becomes good and one can adjust proper air rate
by the damper.</span><span lang="EN-GB"><o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
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</span></span><b><span lang="EN-GB">[RWL2: Understood. I believe this happens quite quickly in a small cookstove of 30-40 cm height. I do not believe TLUD operators have complained about insufficient draft.</span></b><span lang="EN-GB"><br>
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<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"> </span><span lang="EN-GB"><o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">In TLUD (with natural draught) the draught and the pressure losses (thickness of the non-ignited fuel bed and the thickness of the char layer)
change with time (but they are equal according to the above equation). So the air rate changes with time.
</span><span lang="EN-GB"><o:p></o:p></span></p>
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<p class="MsoNormal"><span class="apple-tab-span"><span lang="EN-GB">
</span></span><b><span lang="EN-GB">[RWL3: My question on the linearity of the stove operation (after setting the primary air for a final time) involved the parameters A, B, and C - seemed to be saying that C is generally small - and the “air rate” doesn’t
change very much. That is, perhaps it is increasing viscosity effects (greater depth of char) offsetting the impact of decreasing fuel volume/depth.</span></b><span lang="EN-GB"><o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-GB" style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><b><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Jaakko: The main reason for the natural draught is the difference between gas densities. The pressure losses for flow through a bed of particles
can be calculated by Ergun’s equation. Viscosity has some effect but the main factors are: gas velocity, bed height particle size, porosity of bed (void fraction) and particle shape (sphericity). See Wikipedia for this equation. So with larger particles one
gets lower pressure losses (if gas velocity is constant) and higher gas velocity (if draught is constant).
<o:p></o:p></span></b></p>
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<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">In principle it is possible to solve the air rate (or air velocity through the bed) from the above balance equation in dynamic conditions (as function
of time), because the pressure loss is proportional ~ air velocity ^2 or more precisely from a developed equation for a bed of particles ( Ergun’s equation, 1952).
</span><span lang="EN-GB"><o:p></o:p></span></p>
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<p class="MsoNormal"><span class="apple-tab-span"><span lang="EN-GB">
</span></span><b><span lang="EN-GB">[RWL4: This was easy to find via Wiki - and then other similar equations - including Darcy’s equation. But none of these seem to handle the TLUD geometry and my issue of “C” normally being a small quantity (as experimentally observed).</span></b><span lang="EN-GB"><o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-GB" style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><b><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Jaakko: Look atr Ergun’s equation.<o:p></o:p></span></b></p>
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<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">In practice it is difficult, because the situation is transient heating and the draught in TLUD is also changing (in analogy with initially cool
chimney). </span><span lang="EN-GB"><o:p></o:p></span></p>
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<p class="MsoNormal"><span class="apple-tab-span"><span lang="EN-GB">
</span></span><b><span lang="EN-GB">[RWL5: Except it seems that the draught is pretty constant - perhaps for the “viscosity” reason given above. I am not at all expecting a full balancing - but rather asking what conditions can we have (fuel, etc) that make
the constant drought result possible (again for my reason of wanting to combine primary and secondary air control).</span></b><span lang="EN-GB"><o:p></o:p></span></p>
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</span></span><span lang="EN-GB"><br>
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<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">It has been noticed that the pressure losses are higher for moist fuel bed due to drying so drying of fuel in sunshine before combustion is beneficial
to get lower pressure losses. In the case of TLUD, the hot char layer gives also some draught because the gas is hotter in this layer than ambient air and gas density is lower (than ambient) but it causes also some additional pressure loss. Then, if no damper
is applied along the burning, the air rate (and the burning rate) will evidently increase during the burning (thickness of cool bed decreases and draught increases) and the ignition front velocity changes.
</span><span lang="EN-GB"><o:p></o:p></span></p>
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<p class="MsoNormal"><span class="apple-tab-span"><span lang="EN-GB">
</span></span><b><span lang="EN-GB">[RWL6: Again my own personal testing experience is that the power level (weight loss per unit time) stays quite constant. I am looking for cases where this is true. Of course, stopping stove operation when the maximum
amount of char has been achieved.</span></b><span lang="EN-GB"><o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">The ignition front velocity may be low at first, then reach a maximum and then again could become lower if the air rate becomes high over the maximum
situation (discussed in previous post). However, in this case quenching with too high air rate is not likely to take place, because if the temperature begins to drop, then also air velocity decreases. This balances the air rate to a certain level. </span><span lang="EN-GB"><o:p></o:p></span></p>
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<p class="MsoNormal"><span class="apple-tab-span"><span lang="EN-GB">
</span></span><b><span lang="EN-GB">[RWL7: Not quite sure what you are saying here - but the last sentence “ balancing” is what I am after - how much can there be? How constant can the air flow be in a properly operating TLUD? I am asking the whole list
for experimental data on linear decrease of stove weight.</span></b><span lang="EN-GB"><br>
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<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"> </span><span lang="EN-GB"><o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">So in the case of natural draught, the construction of the device and especially how the draught is obtained, determines the operation. I use wood
chips, pellets, small branches, wood blocks and pine needles in the TLUD (developed by Tom Reed) which has a small blower. All these fuels burn well, but is difficult to use a broad range of fuel types in a natural draught device.
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<p class="MsoNormal"><span class="apple-tab-span"><span lang="EN-GB">
</span></span><b><span lang="EN-GB">[RWL8: Yes, Tom’s fan-powered TLUD was never intended to make char. In his fan stove, char combustion is occurring simultaneously with char production because of the vigorous air flow - no separation into primary and secondary
components, I believe. When you say you have been cooking with a TLUD, is Tom’s the unit?</span></b><span lang="EN-GB"><o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-GB" style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><b><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Jaakko: There are two levels of air rate in this Tom Reed-type cooker. It is also possible to add adjustable flow resistance in the inlet to
decrease the flow even further. One can get much char especially with the lower rate provided that:<o:p></o:p></span></b></p>
<p class="MsoListParagraph" style="text-indent:-18.0pt;mso-list:l0 level1 lfo2"><![if !supportLists]><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><span style="mso-list:Ignore">-<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><b><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">particles are dry enough so that energy from volatiles is enough to preheat the material to ignition<o:p></o:p></span></b></p>
<p class="MsoListParagraph" style="text-indent:-18.0pt;mso-list:l0 level1 lfo2"><![if !supportLists]><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><span style="mso-list:Ignore">-<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><b><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">particles are large enough. For small particles pyrolysis and char combustion can become overlapping (see Saastamoinen, J., Aho, M.,
and Linna, V., Simultaneous pyrolysis and char combustion. Fuel 72, 1993, 599 609). Small particles have larger surface area (which is inversely proportional to particle diameter) meaning higher gasification rate. I get low amount of char with pine needles,
but with wood blocks the yield is high<o:p></o:p></span></b></p>
<p class="MsoListParagraph" style="text-indent:-18.0pt;mso-list:l0 level1 lfo2"><![if !supportLists]><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><span style="mso-list:Ignore">-<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><b><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">particles should be produced or sieved to the same size. It the bed consists of a mixture of sizes, small particles are pyrolysed
fast and their char may partly be combusted in the ignition/pyrolysis front while the large particles are still in pyrolysis stage. If there is a mixture of different sizes, it is best to place particles of approximately same size at the same level in the
bed, but one can have a different sizes in the vertical direction and still have high yield of char. The same applies for a mixture of different fuels (with different reactivity).<o:p></o:p></span></b></p>
<p class="MsoNormal"><b><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">I have used this cooker to boil food with largish wood cylinders and blocks and when the flame reaches the bottom poured the char to a grill
and used the char in grilling sausage.<o:p></o:p></span></b></p>
<p class="MsoNormal"><b><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></b></p>
<p class="MsoNormal"><b><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">In the following I present a rough calculation for primary air rate giving char. Higher air rates (excess air) consumed. The limit case all
volatiles are assumed to be burned in the ignition front. Then equation is <o:p>
</o:p></span></b></p>
<p class="MsoNormal"><b><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></b></p>
<p class="MsoNormal"><b><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Mass flux of volatiles = dry bed density * velocity of ignition front * (1 –mass fraction of char) = stoichiometric mass flow of oxygen = stoichiometric
mass flux of air<o:p></o:p></span></b></p>
<p class="MsoNormal"><b><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></b></p>
<p class="MsoNormal"><b><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">or by using symbols: Mv=roob * w * (1-Fc) = Fo* Mo = Fo * Fa * Ma<o:p></o:p></span></b></p>
<p class="MsoNormal"><b><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></b></p>
<p class="MsoNormal"><b><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">My= mass flux of volatiles (kg/sm2),<o:p></o:p></span></b></p>
<p class="MsoNormal"><b><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">roob = dry bed density = dry mass of fuel/volume of fuel bed (kg/m3)<o:p></o:p></span></b></p>
<p class="MsoNormal"><b><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">w = velocity of ignition front (m/s)<o:p></o:p></span></b></p>
<p class="MsoNormal"><b><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Fc = mass faction of char = 0.2 (if 20% char is obtained)<o:p></o:p></span></b></p>
<p class="MsoNormal"><b><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Fo =stoichiometric mass ratio (mass of volatiles/mass of oxygen) in complete combustion =1.1 (calculated assuming char to consist only of carbon
and using typical elemental analysis of wood <o:p></o:p></span></b></p>
<p class="MsoNormal"><b><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Fa = mass faction of oxygen in air =0.23 (corresponds 21 % volumetric fraction)
<o:p></o:p></span></b></p>
<p class="MsoNormal"><b><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"> Ma = mass flux of air (mass flow rate/cross section area of fuel bed)<o:p></o:p></span></b></p>
<p class="MsoNormal"><b><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></b></p>
<p class="MsoNormal"><b><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">This equation shows that the air rate must be below a critical value to avoid excess primary air for char combustion<o:p></o:p></span></b></p>
<p class="MsoNormal"><b><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></b></p>
<p class="MsoNormal"><b><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Ma < roob * w * (1-Fc)/(Fo*Fa)<o:p></o:p></span></b></p>
<p class="MsoNormal"><b><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></b></p>
<p class="MsoNormal"><b><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Example, ignition front velocity is w=0.4mm/s and dry bed density is roob=150 kg/m3 , we get critical mass for rate of air/bed area Ma < 150
*0.0004* (1-0.2) */(1.1*0.23) =0.19 kg/(m2s). With higher air rate, char is also burned. Of course, some char may also be burned at lower air rate, but the flux of volatiles hinders much of the oxygen to react the particle surface and react.
<o:p></o:p></span></b></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><br>
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</span><b><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p></o:p></span></b></p>
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<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">The operation of TLUD with natural draught depends much on its construction and fuel type and it is difficult to develop any general theory or
model unlike to a forced flow TLUD. It could be possible to simulate the operation numerically with theories of combustion and heat transfer (including combustion of fuel bed, transient heating of different parts of the device etc.), but the calculations would
be device-dependent, quite cumbersome and probably not very accurate and reliable so that experiments would be required for a specific stove construction.</span><span lang="EN-GB"><o:p></o:p></span></p>
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<p class="MsoNormal"><span class="apple-tab-span"><span lang="EN-GB">
</span></span><b><span lang="EN-GB">[RWL9: I agree. But we need more theory than we have had and you seem most qualified to help in this regard. Possibly also Prof. Horttanainen (cc’d) can chime in. My main interest now is in how we can equate the loss
of flow resistance below the pyrolysis from with the gain above it - so that total flow resistance stays relatively constant. Seems that might be a suitable theoretical topic - that assumes relatively constant draft from other effects.</span></b><span lang="EN-GB"><o:p></o:p></span></p>
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</span></b></span><b><span lang="EN-GB">If there are any simple measurements you know of to help establish a best excess (secondary) air quantity, that would be helpful.</span></b><span lang="EN-GB"><o:p></o:p></span></p>
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</span></b></span><b><span lang="EN-GB">I am unaware of any natural draft stove where it seemed excess primary air was present. (Draft was never too much.) Anyone able to cite experimental TLUD work with that character?</span></b><span lang="EN-GB"><o:p></o:p></span></p>
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<p class="MsoNormal"><b><span lang="EN-GB"><br>
<br>
</span></b><span lang="EN-GB"><o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"> </span><span lang="EN-GB"><o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Some cheat device (fan) to replace the natural draught with a forced flow would be a major step to develop efficient cooking devices. Somebody
should invent a cheap fan that uses for example gravity to rotate the fan like in a clock using heavy weights. If high enough air rate is reached, it is then easy to use a damper to control the air rate suitably and get efficient burning.</span><span lang="EN-GB"><o:p></o:p></span></p>
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<p class="MsoNormal"><span class="apple-tab-span"><span lang="EN-GB">
</span></span><b><span lang="EN-GB">[RWL10: Paul Olivier (cc’d) is not a regular contributor on this list, but he has been using a small fan costing only a few $, with a nice speed controller. Perhaps he can comment for us on fan use. His regular fuel is
rice husks - with a low energy density, so his units tend to be tall - not conducive to natural draft. His is one of the few TLUDs with a cap and external supply of (non-fan-driven) secondary air hitting the exhaust gases after they exit through a hundred
or more small holes. His work builds on that of Prof. Alexis Belonio. One Olivier presentation is at </span></b><span lang="EN-GB"><o:p></o:p></span></p>
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<p class="MsoNormal"><a href="http://www.slideshare.net/Jupiter276/paul-oliver-presentation-in-dalat"><span class="apple-tab-span"><span lang="EN-GB">
</span></span><span lang="EN-GB">http://www.slideshare.net/Jupiter276/paul-oliver-presentation-in-dalat</span></a><span lang="EN-GB"><o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span class="apple-tab-span"><span lang="EN-GB">
</span></span><b><span lang="EN-GB">In sum on fans - I am certainly in favor of exploring them, but I also feel we might sell more char-making stoves if we can get acceptable operation without fans.</span></b><span lang="EN-GB"><o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span class="apple-tab-span"><b><span lang="EN-GB">
</span></b></span><b><span lang="EN-GB">Again, many thanks for your many helpful comments. A bit more coming on an earlier message today.</span></b><span lang="EN-GB"><o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span lang="EN-GB">Ron</span></b><span lang="EN-GB"><br>
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<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"> </span><span lang="EN-GB"><o:p></o:p></span></p>
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