<div dir="ltr"><div><font face="arial,helvetica,sans-serif">Hello Crispin, and list;</font></div><div><font face="Courier New"></font><br></div><div><font face="arial,helvetica,sans-serif">In response to the excellent description of Natural draft TLUD turn-down provided by Kirk Harris, you propose the following:</font></div>
<div><font face="arial,helvetica,sans-serif"></font><br></div><div><font face="Courier New"><font face="arial,helvetica,sans-serif">"I can suggest one additional effect to try which is to put a shell around the outside that is closed to the body at the bottom and open at the top. This is a down-drafting secondary air preheater. The height of the upper lip strongly affects the performance so you need to find where to put it. The effect of this is to create a negative draft on the secondary air supply that balances the heat inside in such a way that you get the exact airflow level you want at different power levels. It can take a couple of minutes to stabilize when you make a change in the heating power, but it will settle when the metal changes temperature."<br>
<br> </font><br></font></div><div><font face="Courier New"></font><br></div><div><font face="arial,helvetica,sans-serif">I am trying to get a better understanding of your system for controlling secondary air. If I understand correctly, the mechanism looks something like the diagram below:</font></div>
<div><font face="Courier New"></font><br></div><div><font face="Courier New"></font><br></div><div><font face="Courier New"> | |</font></div><div><font face="Courier New"> | | Secondary air entry</font></div>
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<div><font face="Courier New">| | | |</font></div><div><font face="Courier New">| | Gas Fire | |</font></div><div><font face="Courier New">| |</font></div>
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<div><font face="courier new,monospace"> | |</font></div><div><font face="courier new,monospace"> |///////////////////////|</font></div><div><font face="courier new,monospace"> |//// Fuel-charcoal ////|</font></div>
<div><font face="courier new,monospace"> |///////////////////////|</font></div><div><br></div><div><br></div><div>A) When the rate of flaming pyrolysis is high, the gas fire is strong, and there is a strong buoyancy effect drawing secondary air in. Any effect of preheating the secondary air is minor in comparison to the strength of the draw in the chimney.</div>
<div><br></div><div>B) When the rate of flaming pyrolysis is low, the gas fire is small, and there is a weak buoyancy effect drawing secondary air in, plus the warm metal preheats the secondary air, and reduces its rate of entry by counteracting buoyancy.</div>
<div><br></div><div>Do I understand the principle correctly?</div><div><br></div><div>Cheers,</div><div>Julien.</div><div><font face="Courier New"></font><br></div><div><font face="courier new,monospace"><br clear="all"></font><br>
-- <br></div><div dir="ltr">Julien Winter<br>Cobourg, ON, CANADA<br></div>
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