10 Sep 2014

Seems there are an endless supply of people using wood stoves to create water heaters, even a few who are generating steam for power generation. It's so easy for me to complicate this with ideas use steam mechanical energy to pump hot water, I think first I want to understand how I can get efficient thermal transfer from the heat riser to a liquid, ie water heating. The most common way I've seen on youtube is heaps of copper tube, one guy used 150 feet just for steam!

Ok so this is an awesome rocket stove, just using a tree trunk section and some chainsaw work!


I've noticed the most common pipe diameter is around 3 inch around, and people seem to be getting heaps of heat with this. Mines way more than that, on the previous page, I showed a 3 inch diameter is 127cm sq thanks wolfram alpha! Whereas mine has a 190cm sq feed tube and 255 cm sq heat riser... So I guess if I can get this thing burning really well, it will burn through wood pretty dam quickly.

Heres an example of the narrower pipe diameter producing heaps of heated air:

Another similar steel Rocket Stove with no insulation getting heaps of heat:

I modded air flow for mine:

This is some fence and a couple tin cans, and allows air to flow beneath the timber. So I need about 3 more tin cans to cover the whole thing, and it will need a bunch of holes too so the air can more through to the timber on resting on top.

So the burn box is way too far back, and this means a lot of the burn is happening outside the drum, so I plan on shortening the horizontal feed tube, and making the feed tube more to a design

This guy has made a bomb... the music betrays the impending danger..

So when I modded it with the air tunnel, the cardboard that was forming the mould for the burn tube all caught fire, which looked pretty crazy

After that I figured I need really thin timber to burn which I did, this is about the best I got out of it, with the drum back on top.

This wasn't able to boil a pot of water I had on the top, but I was able to make a coffee, so thats something.. Also when it was going like this there was a constant stream of really hot air coming out the exaust, had like no smoke and just smelled of the timber. So perfect for a space heater heating a cob bench, but not for focusing heat on a small area.

Heres mine!

Heres a guy whos made a spa heater which runs only on wood fuel:

Need to think more about a heat exhanger with good efficiency, this is complicated by not having a pipe diameter for the heat exchanger, common copper diameters are 12.7mm (~AU$5 per m) and 19mm (~AU$10 per m). Theres also copper with fins, which would have better heat transfer but not as easy to source.
Just thought of something. Could have a tank of water on the inside of the steel drum, which the smoke passes across.. mm complicated...