ARC E-Newsletter 8/6/25: Concentrator Disk/Chimney in a TLUD

[Aprovecho Research Center]

Concentrator Disk/Chimney in a TLUD

When I asked Google AI, “Is flow more laminar in a smaller diameter tube?” it immediately responded:

“Yes, thanks for asking! A smaller diameter tube can promote more laminar flow for a given flow rate. This is because reducing the diameter of a tube increases the Reynolds number, which is a dimensionless quantity that helps determine whether flow is laminar or turbulent.”

I had been noticing that the chimney also increased draft in a TLUD we have been developing, lengthening the rising column of flame.

As a rule of thumb, Dr. Winiarski advised that flame should burn out before it touches the bottom of the pot. Yellow flame is very hot (around 1,100C) which is great, but sufficient mixing and residence time are also needed to burn up smoke.

Have you also experienced that lifting the pot off of the top of a TLUD can reduce the emissions of PM2.5?

Reducing draft by removing the concentrator disk/chimney this week has allowed flame enough time to burn up more smoke in a relatively short TLUD. At the same time, thermal efficiency has been reduced when short flames dance playfully on top of the larger diameter combustion zone (with a larger Reynolds number).

---

Find the new book "Improving Biomass Stoves 2025," resources, publications and information about our work at www.aprovecho.org

Find archived newsletters online at aprovecho.org/newsletters
© 2025 Aprovecho Research Center/Advanced Studies in Appropriate Technology
76132 Blue Mountain School Road, PO Box 1175, Cottage Grove, Oregon, 97424 - USA
(541) 767-0287 • www.aprovecho.org