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</o:shapelayout></xml><![endif]--></head><body lang=EN-CA link="#0563C1" vlink="#954F72"><div class=WordSection1><p class=MsoPlainText>Dear Martin<o:p></o:p></p><p class=MsoPlainText><o:p> </o:p></p><p class=MsoPlainText>Several good questions so a little background.<o:p></o:p></p><p class=MsoPlainText><o:p> </o:p></p><p class=MsoPlainText>There are three approaches that I have seen used so far, with the ones I mentioned that are using air flow instead of a metal part being omitted from the list. This is just for metal parts:<o:p></o:p></p><p class=MsoPlainText><o:p> </o:p></p><p class=MsoPlainText style='margin-left:36.0pt;text-indent:-18.0pt;mso-list:l0 level1 lfo1'><![if !supportLists]><span style='mso-list:Ignore'>1.<span style='font:7.0pt "Times New Roman"'> </span></span><![endif]>The use of a flat disk with a hole in the centre that brings fire and smoke together so the flame does not let the smoke get away. This is especially important if the physical distance from the fuel bed to the flame is short because the fire may burn well on one side of the bed and not on the other, then later the position switches. <o:p></o:p></p><p class=MsoPlainText style='margin-left:36.0pt;text-indent:-18.0pt;mso-list:l0 level1 lfo1'><![if !supportLists]><span style='mso-list:Ignore'>2.<span style='font:7.0pt "Times New Roman"'> </span></span><![endif]>The use of an upward facing cone which I used on the Vesto coal stove when trying to get a much more difficult fire to burn continuously. I showed that to Paul on one of his visits.<o:p></o:p></p><p class=MsoPlainText style='margin-left:36.0pt;text-indent:-18.0pt;mso-list:l0 level1 lfo1'><![if !supportLists]><span style='mso-list:Ignore'>3.<span style='font:7.0pt "Times New Roman"'> </span></span><![endif]>At that same time Paul and John Davies were working together on John’s packed bed coal gasifier and John introduced a change to the air supply, putting a Vesto-like sleeve around the hot combustion chamber but instead of leading the secondary air into a space with an upward flow, he introduced the air via a cone, working in such a way as to blow the air downwards towards the top of the fuel – the opposite of the one I showed Paul. Well, nearly the opposite. The effect was to produce a very hot fire at the top of the coal when it was coldest and needed the most heart applied as soon as possible.<o:p></o:p></p><p class=MsoPlainText><o:p> </o:p></p><p class=MsoPlainText>These three methods all hold open the possibility of using preheated secondary and all three can use the counter-flowing method of heating it, though only 1 does. The World Stove by Nat kind of does but it burns in a different way so I will leave that as a separate system.<o:p></o:p></p><p class=MsoPlainText><o:p> </o:p></p><p class=MsoPlainText>If the system is using counterflow preheating like a Vesto the secondary air should be drawn into the stove body at an upper level and pulled vertically downwards so that heating the air tends to make it resist flowing down. The advantage of this is there can be considerable control over the total mass of air flow. When the air enters the bottom and rises vertically, such as in the packed bed gasifier of John Davies, the flow has to be controlled mechanically, which he accomplishes using a rotating sleeve.<o:p></o:p></p><p class=MsoPlainText><o:p> </o:p></p><p class=MsoPlainText>For those who have not yet tried a counterflow secondary air supply I encourage you to try it to see it if reduces and self-controls the excess air ratio. When you get it right, the excess air remains under control across a range of power levels – a considerable advantage for a domestic stove.<o:p></o:p></p><p class=MsoPlainText><o:p> </o:p></p><p class=MsoPlainText>As to the ratio of the constrained area of the hole and the area of the combustion chamber, there is no standard ratio. In fact what is more important would be a maximum diameter or area per kW of total power. If the stove is small (1-2 kW) the hole should be about 45-55 mm in diameter. If it is 2-5 kW, 50-65mm. Above that more area is needed. It must not overly constrain the gas flow. Experiments are being conducted right now on a Keren stove in Yogyakarta to find out how much the pinching should be. So far the 2-pot Keren stove needs a 55mm diameter tube or hole (A tube works better than a hole).<o:p></o:p></p><p class=MsoPlainText><o:p> </o:p></p><p class=MsoPlainText>Regards<o:p></o:p></p><p class=MsoPlainText>Crispin<o:p></o:p></p><p class=MsoPlainText><o:p> </o:p></p><p class=MsoPlainText><o:p> </o:p></p><p class=MsoPlainText><span lang=EN-US style='mso-fareast-language:EN-CA'>+++++++++</span></p><p class=MsoPlainText><o:p> </o:p></p><p class=MsoPlainText>Paul, Paal, Crispin and all,<o:p></o:p></p><p class=MsoPlainText><o:p> </o:p></p><p class=MsoPlainText>A lot of time ago I asked myself if "diaphragm" by T-LUDs could be an even adequate name instead of concentrator-disk. <o:p></o:p></p><p class=MsoPlainText>- That expression would lay the accent on restraining the flow, which I guess, could be as well of importance as concentration.<o:p></o:p></p><p class=MsoPlainText>- Just a thought on the function, not a suggestion to change the name of the disk-.<o:p></o:p></p><p class=MsoPlainText><o:p> </o:p></p><p class=MsoPlainText>Regards<o:p></o:p></p><p class=MsoPlainText>Martin<o:p></o:p></p><p class=MsoPlainText><o:p> </o:p></p><p class=MsoPlainText>P.S. the cross-section ratio: hole to metal-disk is _always_ 1 to 1 ? <o:p></o:p></p><p class=MsoPlainText> - That means: The radius of hole- and disk-diameter differ by the factor root of 2 .<o:p></o:p></p><p class=MsoPlainText><o:p> </o:p></p><p class=MsoPlainText>By all described T-LUDs I saw this ratio; or are there other/different ratios ?<o:p></o:p></p><p class=MsoPlainText>Is there a _simple to understand_ explanation for that ratio, beside "that works best" ?<o:p></o:p></p></div></body></html>