I've been learning Sketchup and drafted some J- tube designs.
The first one is a 4 inch cook stove that I built in the real world.
Here's what I wrote for the descriptiion.
This is a mock up of a stove I made in real life. I used a variety of salvaged bricks, mostly pavers and a few fire bricks for the top of the burn chamber. I used cob for the mortar.
This design provides excellent draw, burns clean and efficient.
I've fried a bunch of egg sandwhichs, canned tomatoes and cooked pasta with small amounts of wood. However I find that I need more heat for doing things like boiling water. Next, I'll design and build a 6 inch system as part of my outdoor kitchen.
My next designs will likely include a barrel of some kind. While the current version burns "clean" I still get soot on my cookware. A barrel will prevent that and perhaps make for an even hotter system.