Peter van den Berg

Benjamin Dinkel wrote:And if the core isn’t within a bell the core surface counts as well. And a barrel obviously counts too.

No, the core surface won't count as part of the ISA. Internal walls and ceiling of the bell is what we are talking about, not the outside of whatever part is sticking out of it. A barrel is also part of the ISA, that's true.

What I use as the simplest calculating method: count all the walls and ceiling as if the core wasn't there at all.
The core, when in the bell will extract heat at first but radiate out again later. When the core is sticking out there need to be something around it, otherwise it will be much too hot. Most of the time there will be a second wall around the core to dampen the heat, in that situation.

Glenn Herbert wrote:A J-tube with natural draft not needing the chimney warmed to burn well, I believe, could work fine in a larger bell while taking longer to store as much heat. The ISA of my bell is irrelevant to the early functioning, when any size bell would still be cold.

Forgive me Glenn, for not mentioning why the above statement won't hold, so here we go.
Of course you are entitled to believe whatever you like.
But... there is a certain effect that is firmly based on physics, the kind that won't be influenced by faith. That effect is mostly referred to as "chimney stall". About +/- 20 minutes into the burn, the exhaust gases into the chimney need to be warmer than 60 ºC (140 ºF), otherwise the chimney draw will cease to exist and all smoke will stream into the house. What I mean with temperature measurement, is done in the very center of the chimney pipe, where the stream has its highest temperature and velocity.

I stumbled upon this phenomenon many years ago and it took a lot of time to understand what the hell was happening. As you may know, combustion of woody material will produce heat (obviously), CO² and water vapor. Quite a lot of the latter, about half a liter of liquid water for every kilogram of bone dry fuel. Translated in imperial measuments: 30.5 qubic inches of water for every 2.2 lbs of dry fuel. As such, it is a by-product of the combustion process, much like natural gas. When the fuel wasn't as dry to begin with, this water content will be added to what is going into the chimney.

For now, we concentrate on the water vapor. This will be sent into the chimney and when the temperature is low enough, something between 40 and 50 ºC (104 and 122 ºF), the vapor will condensate on the chimney wall into liquid water and runs down. Lower in the chimney it's warmer, so the water evaporates again and is added to the vapor that's already there. So it rises into the chimney, but since the gasses are more saturated with water vapor now, it will condensate in an earlier state and lower in the chimney so it runs down again. This process will be repeated over and over again, consuming more and more heat, until there's no more heat to carry the vapor to the outdoors and the chimney will reach the state what we call "stall". No more draw, all smoke and water vapor is streaming into the house.
Sometimes, the stall can be deminish by itself and the draw seems to be restored. But in almost all cases, within minutes the chimney stall shows up again.

If you like to check the above explanation, extend your bell by 100%, start the thing up stone cold and watch what happens.

Hmmm... In October 2015, I started out with a 6" batchrocket and a bell of 64.6 sq.ft (6m²). The chimney being 6" (15cm) diameter, insulated and straight up. It was a complete disaster, the darn thing refused to play ball for two weeks straight. I brought it down to 53.8 sq ft (5m²) and it was managable, it was willing to work. Just before this 11th heating season I brought the ISA up to 57 sq ft (5.3m²), not accidentally the accepted maximum ISA, and it still worked. Although I had to be very careful not to rush a cold heater into full burn. This particular heater doesn't sport a bypass, by the way.

So, you are saying that your 8" J-tube is coupled to a 50 sq ft bell and works well. I think you are right here, this could be a little bit larger and still running well, in my opinion. But I highly doubt this same J-tube core would run as well with a bell with an ISA that's double what you have, 101 sq ft (9.4m²) to be precise. That's the maximum ISA size an 8" 1st generation batchrocket could serve without running into problems.

What I meant to say is this: in about 13 years, time and again the J-tube proved to be about half as powerful as the 1st gen. batchrocket for the same size. This isn't speculative, or an opinion, just hard numbers and the result of literally hundreds of experiments.

Glenn Herbert wrote:A J-tube the same system size as a batch box will eventually heat up the same bell fully. How long it would take depends on the specifics of the situation.

Not quite correct, sorry about that. Having a J-tube of the same system size as a batchrocket doesn't mean they have the same power output. Which means the batchrocket bell is grossly oversized when combined with the J-tube. Without a bypass of some kind, the J-tube won't come up to clean burning temperature at all.

Been there, done that, learned from it.

Scott Weinberg wrote:Please read-  This is only my experince, I am not suggesting or implying your results will be the same.  But without gages, recording, and study, it would only be a great working warm stove.  now it is a on going experiment daily.  

I fully agree. Point is, the guys and girls of the shop have other things to do than to try to get "the most out of it". The place isn't mine, the heater isn't mine, as soon as the work was done it was out of my eager hands. That said, I built up a lot of goodwill, and I am very welcome to bring visitors with me to show the heater, offer them coffee and a chair to "sit by the fire" with me as the proverbial storyteller...

tony uljee wrote:so i can only hope that this will be noticed by other interested companies/customers----who can get Peter to build another stove ---or at least under his guidance-----thankyou  Peter.

Your welcome. Tony. In the mean time, there is a another heater built under my guidance, I am convinced you didn't miss that one. See the  following heater report, which obviously (or at least I hope it does!) bears my signature. This guy did the design himself, I only did steer him in the right direction a number of times.
https://permies.com/t/364721/Transforming-Fireplace-Splendid-Rocket-Mass

Glenn Littman wrote:Magnificent Peter! Congrats on your efforts and creating another masterpiece. Has it been named yet? I'll toss out a few thoughts that come to mind... Godzilla or perhaps Gargantua.

No name so far, not sure it will come that far, to be honest.

Glenn Littman wrote:I didn't see any mention in your build commentary... did you embed any thermocouples in the mass? It would be quite interesting to see what the inside skin temps are running. I actually find that monitoring my inside skin temps helps me to manage the external skin temps better as it will give an advanced idea of system temperature profile.

Yes, that's true, but there aren't any thermocouples in the mass. Running the heater isn't a task of just one dedicated person. Everybody has their own work to do during opening hours, so every now and then somebody shoves a couple of fuel pieces in the firebox. This is how they do it now, that might change when frost kicks in.

Glenn Littman wrote:Once the system is fully dry it will be interesting to know the firing cycles to get it up to temperature and maintain it considering the enormous mass. It will also be interesting to see how it retains the heat over the 35-40 hours that the store is closed and the external temperature when they reopen on Monday.

At the moment, they use the clever thermostat of the gas heater as temperature gauge. It is able to show the temperature over each 24-hour period, hour by hour. So they'll know what temperature decline is going on during closed hours.

Gerry Parent wrote:Question: Curious why the ceiling of the bell had regular bricks instead of firebricks, especially right above the riser exhaust port?

The spot with the highest thermal stress is right opposite the exhaust opening. The ceiling is getting warm, yes, but not overly so. I reckon the surface temperature of the concrete won't get very high, the material sports a relatively high conduction rate. Remember, this is a large heater with lots of space inside. The heat will spread out fairly quickly, to date there is no report of loud BANG! noises, indicating bricks cracking up. The same goes for the small Pepper shaker in my workshop, no frightening noises. The inner wall of the large heater should be hotter than 520 ºC (968 ºF) before the quartz christals are breaking up.

Gerry Parent wrote:Also, I noticed a latch on the door which appears to do something for the air inlet flapper. Is it to lock the flapper closed when the fire is out?

The guy who did the welding rated the work on a decent flap as too complicated and choose to do something else. The latch is a quick bodge to close the flap. Simple, not sophisticated at all. As long as it works, not my choice but it'll be OK.

Cristobal Cristo wrote:Also the dark color of the bell helps with faster heat radiating.

Yes, it helps. But what helps a great deal more is the thermal conductivity coefficient in the concrete clinkers. This is about 2 to 2.5 times greater as compared to hard red brick. Which makes the heater relatively quick responding, despite such a huge mass.

Julian Adam wrote:Incredible result, congratulations Peter & helpers! Are they topping it up all day long to have sufficient heat output? Almost a pity to cover it in clay plaster!

Yes, they are topping it up all day long. Which means it is refilled every 2hours or something like that. At the moment with soft wood fuel, since they have a lot of pallets and crates lying around. Normally, they have to pay for to get rid of the stuff, now it's generating heat. The formerly used cast iron stove couldn't really be run with soft wood at all, far too much hassle.
I agree about he plaster, there's a possibility they'll skip that eventually.