Peter van den Berg

Nono Junang wrote:The second box of bricks is not a bell but rather a channel flowing like a snake (not straight) with opening going right / left / right.
I have made this to increase the path of the exhaust so that it gives even more energy to the bricks. The height of that channel is 1.7m.

What you did is making the gas path longer, this is what the Austrians do. Just to let you know batch boxes are particular picky about friction in the smoke path, that's why I always advocate bell constructions cause they are virtually frictionless.

Nono Junang wrote:I plan to cap the top of the first bell with a plate of stainless steel 1.5mm thick. I would also like to make a 200mmx200mm opening on that plate just on top of the heat riser and place a glass there. In addition I would like to have a mirror on the ceiling right on top of that glass so that I can have a view of what is happening inside the heat riser from the top.

A steel plate of 1.5 mm thick will warp badly at that location. Think of 15 mm thick and possibly a cross welded underneath to make it more rigid.
That glass will stain with soot during the start of the burn, and will turn to white when the temperature goes up. But in my experience this isn't worth the effort, you won't see anything after a few burns.

During the Innovator's gathering in Montana Erica Wisner tried a 2" batch box core entirely built of insulating firebricks. The thing needed a longer riser in order to get it going. And it could only be run with nothing more than chop sticks size fuel. Conclusions: there should be a real fire in there, not a smoldering pair of small logs. The fire can't be scaled down that far and insulation is an issue in the sense it shouldn't be scaled down as well. Smaller burn chambers are disadvanteous due to the unfavourable volume / wall surface area ratio.

I've built a number of 4" batchbox rockets  myself and in my opinion it could be done. But you need to keep feeding it in order to achieve a clean burn longer than some minutes.

Graham Chiu wrote:Anyone have a clearer idea of why these pyrex doors shatter? Are they being exposed to more than 500 deg C?  Have they shattered just sitting there, or is it thermal shock?

When the glass shatters in little crumbles it isn't pyrex but tempered glass instead. When it cracks in a non-straight line it is pyrex which happened to be borosilicate glass, maximum heat resistance is up to 500 ºC. The real stuff is special ceramic glass, heat resistant up to 900 ºC and insensitive up to a certain level to heat shock. This ceramic stuff is sold under the names of Robax or Neoceram, only two producers in the world as far as I am aware of.

Edit: I've never seen a piece of Robax to shatter or even crack. Not even in very extreme circumstances, provided it is able to expand.

Taking an old-fashioned woodstove and glueing a riser to it doesn't mean it becomes suddenly a clean burning efficient wood combustor. The proportions of the firebox need to be right, the port size need to be very precise and the riser insulated and high heat resistant.
There are some projects been done like this, but the wood stove needed quite a rebuild.


This video is in French but the process is self explanatory.
Maybe the 5-minutes riser is something you could use? it consists of a large diameter steel stove pipe and a superwool liner inside. Also, read the comments.
https://www.facebook.com/photo.php?fbid=10154992096951974&l=3e4ec1844f

Dan Hatfield Ii wrote:Do you have any resources (sizing or maths) in bell bench building (stratification chambers).
I’m considering going that route to save money and time on flue fittings.

A bell bench isn't any different as compared to an upright bell. Please use the tables given on the website. In case the bench is built as a second bell deduct 15% of the total cross section area of the system.

Jeroen,
By the look of it in the drawing, the woodstove seems to be a Turbomasse stove. That type of stove does need a lot of draft to work properly so cooling down the exhaust gases won't work, the chimney need to be quite hot in order to keep the thing going. To be frank, just adding a bench or other heat extractor to a random stove is bound to fail. In case it does work, it'll come together with a lot of pollution and tar dripping out the chimney pipe.

In januari of this year, Uzumé association tested such a construction and it failed miserably.
Here's the link, the website is in French but Google translate is quite good at what it is set out to do.
http://uzume-asso.org/session_batch_2018.html#turbomasse

Specifically for how bell systems are done, see http://batchrocket.eu/en/building#belltheory

Satamax Antone wrote:Hey Peter, no worries.
I must not have been awake yet! Have you heard this one? I'm pretty sure i know how it can be replicated. Well, kindof.

OK, the first one is what I meant with a rapid pulse. Hard to count but it seems to be something between 35 and 40 pulses a second. I didn't know about this one, although it's published nearly 3 years ago. I am all ears how it could be replicated, imagine one could run such a small thing with pellets and get this type of performance!
The second one is the slow pulse, the Testo won't be happy with this for sure.

Satamax Antone wrote:Is your's pulsating like this,

 
If yes, that's bad.

As always, I hate to contradict you Max. A slow pulse like twice or 4 times a second is not good, I do agree with that. But in order to know what speed the pulse in the video was going I slowed it down at the time and calculated it as something like 40 times a second, much like a pulse jet engine. The Testo gas analiser confirmed it was a very clean burn while the fuel was racing through as nothing else. Together with absolutely top temperatures of the small drums as the result. As far as I know of, nobody has mimicked this behaviour until now so it might has been the result of a number of specific circumstances.

So I wouldn't regard this as a good example of a pulse like a steam engine, and I might stress again such a slow pulse is considered wrong behaviour of the heater.

Geoff Laughton presented this rocket stove water heater in a video published May 12, 2013, that's true.
However, the guy who built it is someone else, his name is Tim Barker. He built this appliance and wrote an article published November 23, 2012 by Permaculture Research Institute.
Here's the article, complete with diagrams of its workings.
https://permaculturenews.org/2012/11/23/rocket-stove-hot-water/

Tim built other water heaters based on rocket stoves, notably in Missoula, Montana during the Innovator's Gathering 2014, to name one event.