[Stoves] TLUD Design and operation

[Crispin Pemberton-Pigott]

How's this, Norm:

A sharp edge, two soot formation paths. One is electrical and the other is temperature.

Sharp edges are used to dissipate electrical charges (aircraft, for example). As combustion involves separating atoms from molecules, there are charges roaming all over the show. Ions, charged particles...

So the most likely place a charge will be noticed is at the tip of something sharp.  The most likely thing to be attracted to the points is charge-bearing free carbon because there is simply so much of it.

This phenomenon is also noticed inside the evaporators of kerosene stoves. Heating the fuel evaporates it and there is thermal decomposition creating free carbon with one or two charges. At the the entrance or exit of the jet, there is high velocity gas creating a static charge on the metal. The carbon tends to deposit on the sharp edges to dissipate the charges. This accumulates as soot, builds, breaks off and flows with the gas, and blocks the nozzle.

This problem requires the user to use a thin wire to unblock the nozzle. The tool is known as a "pricker".  Sometimes this has to be done quite frequently to keep it burning. This problem can be minimized by polishing the edges inside - so generally the jet and holder are polished to remove all internal points and sharp edges.

On the TLUD, the sharp corners can be radiused as well as can be managed, and the effect will be limited to some extent.

The second cause could be temperature. The metal next to the sharp edge probably has little gas contact, which means the area around the "sharp" is radiating while not being so much heated. The edge will be cooled by the nearby material, placing a chilled contact point in a passing evaporated stream of volatiles almost in the gas stream.

The result is an accumulation of carbon and carbonaceous particles on the "corner" due to condensation alone.

Clearly these two effects may also be combined.

Regards
Crispin

From: ntbakerphd at gmail.com
Sent: August 24, 2019 2:01 PM
To: stoves at lists.bioenergylists.org
Reply to: stoves at lists.bioenergylists.org
Subject: [Stoves] TLUD Design and operation

Recently we had some discussion about TLUD design and cookstoves. The TLUD Summit was very beneficial. Currently building version 24.

One recent comment from someone discussing TLUD design was that (as I recall) "sharp corners result in the formation of soot in the exhaust stream". I assume this means sharp corners in the metals used in the stove. My interpretation is the metal sunflower or turbulator used in many TLUD cookstoves.

 Or is it sharp corners in the spaces where combustion and/or pyrolysis occurs?

Does anyone have any ideas or comments or experience on that issue?

Thanks,

Norm
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