Internal wall count against total ISA ?

[belgiangulch]

Hi All;
Building a brick bell heater in my shop. Trying to figure out how tall I can go. I know the ISA is 4 walls and the roof.
I have built a blocking wall inside my bell. Full width , dry stacked with plenty of gaps. Large opening at the floor and open all the way across the top.
Currently this wall is 3' wide and 4' tall. The outer bell walls are currently closing on 5' and if I can, I want to go up to 6'. So a 12" minimum gap over the wall and possibly up to 36"+ IF... I can successfully build an arched dome over 2/3 of the bell.

My question's; Do I count both sides of this wall as an apx. 24'addition to the ISA ?
One side as a 12' addition?
Or is this wall, with it being open at the top and bottom not count at all ?
If this wall does count (as I suspect it does) then would the 4.5" width of that wall be deducted from the total length of the outer wall ?

[peterberg]

Building a column or columns inside the bell will increase the total ISA, yes, and is quite common in Russia for example. All the surface area which can be touched by the exhaust gases count as such. Building a wall too, but as such it divides the bell in two separate parts or so I think. Walls are influencing the gas stream of course, but the main question is: the side where the riser is situated, is that large enough to qualify as a real bell? The fact that it's open at the floor and the ceiling doesn't ring a bell to me, I honestly don't know what the effect will be. It's a gamble in my view, you are running the risk to have to demolish your bell because it might be faulty.

[belgiangulch]

Hi Peter; Thank you for replying.
Let me try to explain what I am doing and see what you think.
This is an 8" J tube ,with a ceramic board core and 5 minute riser run into a 55 gal barrel. There is a 12" top gap.
From the barrel, it drops into my single bell. That bell has an inside measurement of apx. 4' x 3'. Height is yet to be decided.

The dry stack wall that I built is directly across from my barrel, it has a 9" x 9"opening floor height on the north corner.
Behind that wall at floor height on the south corner is my exhaust outlet for the bell.
My reasoning for the building the wall was to keep the hot gasses from heading directly towards the outlet. I also was wanting to add ISA and mass to the build.
I was considering bringing that wall up to the ceiling level and creating a second bell.
I have also considered just leaving it at it's current height to add mass, ISA and direct the gasses away from the outlet.

It is not to late for me to reconfigure or remove that wall if you believe it might be not such a good idea.
Those same bricks could be stacked into columns to gain mass and ISA if you think it would be a better idea.

I intend to give this bell a temporary flat roof of 1/2" hardy board for the rest of this burning season and then I hope to give it an arched dome similar to the "casserole" door build that Kirk built at Paul's.

[peterberg]

Dec 22, 2018 16:13:55 GMT -8 belgiangulch said:

My reasoning for the building the wall was to keep the hot gasses from heading directly towards the outlet. I also was wanting to add ISA and mass to the build.

A well-designed bell (i.e. wide enough) will prevent the gases to go directly to the exhaust. Building a wall in the middle could disturb the natural tendency of the warmer gases to rise. The thing with a bell is: don't try to steer the hot gases, make use of their natural behaviour. What you could do instead is stacking columns inside, generously spaced from any wall. Building those column(s) with mortar between the bricks has the added advantage it could be used to support the roof or dome. A good column is with a square footprint, each layer two bricks on flat and every next layer turned 90 degrees.

Of course it will add mass and ISA this way. Keep in mind the barrel is acting as a bell as it is since there's a 5-minutes riser in there sporting a one foot top gap. So the brick bell is actually a second bell. From the pictures on permies I understand you built this bell right against the barrel. This isn't a good idea, better to keep steel and bricks separate otherwise there will be cracks and leakage. Is it possible to bridge the bell so it could be separate from the barrel?

And yes, you could give this bell a flat roof out of hardy backer board. It would be wise to stack bricks on the edges to keep it in place, there's a risk it would warp. Concrete lintels or such things could be used to close the top since it's a second bell and won't be as hot as the first. I honestly don't know how large a bell system could be for an 8" J-tube system. But just start with the idea it can serve as much as a 6" batch box one. That would be, including the inner surface of the barrel walls and top 57 sq.ft.

Hope this is clear.

[belgiangulch]

Thank You Peter;

I will follow your advice and remove that wall.Then build at least one column in its place.

About the barrel.
For about 2' on the north where the brick ends and the same on the south side at the tight spot. The brick comes as close as 1/4"or less , but not touching.
After I trim each brick to fit, I have cut a slice of Super Wool and placed it between brick and barrel. Sealing it with sandy fireclay. My hope is that this will act as an expansion joint as the barrel heats and cools.
If not then, it will mean repeated application of cob to keep it sealed until a later date. Hopefully when its warmer outside...
The hardy board roof will reach across north to south. Where it passes by the barrel, I will cut a semi circle as close as I can. 1/4" hardware cloth screwed to the barrel and heavily cobbed should seal it to the roof.