Will this work? Brick placement for single bell J tube RMH

[whazzatt]

This is the kind of thing I've done before:



Now I wish to add a 'bell' to increase efficiency. Please do not be intimidated by the technicality of the drawing :



I have not cut any bricks but will when I get some confirmation that this will work. Burn chamber and heat riser brick placement pictured below; please imagine the bell being on the left, as in my drawing:



This would be the rough size of the burn chamber:



Is the entry from the heat riser too big? It is roughly the same size as the entry from the burn chamber to the heat riser. What would be the ideal size of this hole? (Remember, this hole will feed into a brick 'bell'):

[satamax]

Entry into a Bell. 1.5 or 2 times CSA.

[whazzatt]

Thanks Satamax.

Took me a while to find that CSA is cross section area.

Maybe you could help me a bit more...

Based on the way that the bricks fit comfortably together (in a new arrangement of bricks, not the arrangement pictured, which is too big):

The riser has a CSA of 172 sq. cm. 

The throat from the burn chamber to the riser, however, has a CSA of 132 sq. cm.

Which CSA do I consider? 

And importantly, does the same rule apply for the chimney flue exiting the bottom of the bell? I.e. the rule being 1.5 or 2 times CSA. I think I have screwed up massively by purchasing piping and elbow bends of 50 sq. cm!!  

[satamax]

CSA should be the same everywhere.

[Orange]

also the feed tube cant have double CSA, that's why BB exists.

[pinhead]

The cross-section of the feed, throat, and riser all must be the same (and should be square, round, or some other approximation of either). It looks like the feed is too "long."

The area feeding into the bell (called the manifold) should be as large as possible but the minimum size is 1.5 times the area of the J-tube.

[whazzatt]

Awkward space to work with, because I think it would be crazy to remove the massive 380 cm2 CSA flue that has a great draw to it, so the idea is to work with it and build a brick chimney to meet the flue. Obviously I haven't built up the walls in this temp setup, so a bit of imagination needed...



I haven't cut bricks yet, so the placement is purely to give an indication of the shape of the thing - I'll do proper 'alternating layers' of bricks when the time comes. The idea is to have the brick bell at the back, doing a turn on the right, and then the cooler gases enter at the bottom of the chimney via another turn. Here's exit from riser, double brick height:



The CSA of the burn chamber is same as initial part of riser. Top of chimney opens up a bit and enters bell via a much bigger CSA opening. The opening from bottom of bell into chimney is the same as latter most port: 



The hope is that the massive flue and its constant draw will ensure a nice pull through the unit.

Thoughts? 

[whazzatt]

Done a massive amount of research for this build. Found THIS (Donkey's adobe 6 inch dragon core thread) and it has become what I'm hoping for.

As said in previous post, tough space to work with because I want to use the existing flue.

I have not cut any bricks yet. Will get there. 







The gap around the bell: I plan to use strong fire cement over off-cut fibre board. Only concern is if the horizontal part of the manifold is a bit small as an entry into the vertical part of the manifold into brick bell, pictured previously. 



Any help will be much appreciated. I want to start the clay/sand/fire-cement mortaring of the bell and chimney bricks soon...

[travis]

Any update on your build?