Heat riser to exhaust, where is the connection?

[fairbanks1981]

I've read through the book a couple times, watched some videos and looked through the posts here.

I still do not understand how the hot air is channeled to the exhaust from the heat riser. Looking at the cross section pictures doesn't help me since the 55 gallon barrel that goes over the heat riser is round and the circumference is larger than what it is covering right? If you want the air channeled to your 8" exhaust pipe what do you do with the rest of the gap that is all the way around your barrel?

Looking at the pictures it would seem as the air leaves the heat riser it would hit the top of the barrel then get pushed to the right and down the barrel towards the exhaust? what keeps the air from going anywhere else? Do you fill around the bottom of the barrel with cob until you get to where the exhaust will be? This is just difficult for me to imagine in 2D.

[spacevan]

Yea from the pictures that i have seen you can weld an 8" male pipe end near the bottom of the barrel and the rest of the barrel is sealed with cob, or the barrel is cut out so it sits over the 8" exhaust and is sealed with cob. i know that other people hear can give you a better answer to your question but its a start.
This link shows a video of setting the barrel on a heat riser
www.youtube.com/watch?v=x9jgs-aA7Ck
This is the 6th video of a 6 part rocket stove build, thoes videos will probably answer alot of your questions.

[Donkey]

Exhaust flows out of the heat riser, hits the top of the barrel, flows down the gap (all around) between the riser insulation and the barrel, then it flows into a shape usually made of cob and/or brick that is somewhat difficult to describe which channels the flow into the (bench, etc.) stovepipe.
The shape, more often than not, looks like a doughnut shaped slot, fatter at the stovepipe end and is designed to gather exhaust towards the pipe.
I don't really like the welded pipe-into-barrel configuration because it's pretty likely to be a bottleneck. The space there needs to be AT LEAST the same volume as the pipe, if not just a little bit more. It's the gap between the barrel and heat riser insulation, the gap ALL the way around is supposed to be rather narrow. It's total area should be close to that of your system size, or at least as close as is easily obtainable. If you weld the outflow to the barrel there, you're likely to make a choke-point.
They tried to describe it in the book, though I don't think it quite did the trick. I've been trying to find an image in my stuff that might help, no dice.

[fairbanks1981]

Thanks, this does help somewhat. Kind of as I expected it seems you just kind of mold the cob around the bottom but leave space around where you want your exhaust, keeping in mind the required pipe dimensions.

I'll just have to experiment!

Thanks guys.

[blackearthbert]

If you look at my blog you can see my steel fabricated hot gas discharge box with a clean out.

blackearthrocketstoves.blogspot.com/

The bottom of the barrel is sealed in COB or mortar and a small shaped chamber is shaped below the barrel and behind the Box using fire brick or castable refractory..

I'm just installing a Rocket in a greenhouse and I'm documenting it as I build. I'll get some picts up on the blog in a few days. Should be doing the Hot Gas Discharge box connection before this weekend.

Regards
Bert