Transition Area Rebuild Questions

Hey, folks. So, I'm rebuilding my heat riser and transition area. I've made the transition bell out a whole bunch more.

Here are my questions/concerns.

1. I'm including a photo of the new transition bell I made, and it's a bit higher than where the bottom lip of the barrel will rest. So, I'm wondering it that's okay, or if I should cut out a dip in the barrel to meet the shape of the bell better. ... I'm having a hard time getting my attachment to upload, so here is a link to the image on Dropbox: https://dl.dropboxusercontent.com/u/4437344/20140829_122519.jpg

2. I've never gotten a clear answer that I'm satisfied with about what kind of material/mortar to use right around the barrel, where it's going to be really hot, and needs to be really sealed. I have fire-clay, and the clay I got for cobbing. What's best?

3. It was suggested to me to use chicken wire instead of the sheet metal I had used to contain the insulation on my heat riser, because the sheet metal may have been getting too hot. I don't like the idea of using chicken wire, because it sounds hard to get an exact shape with it's willy-nilly nature. I'm thinking of using some metal lathe that I have extra of. Any thoughts?

Thanks!

Hi John; I'm no expert having built only 2 of these , but for what its worth here goes, #1 ; if it were me I would notch the barrel just to make sure . #2 I used a fire clay & sand mix to seal my heat riser and also my 55 gal barrel, then with the 55, I switched to regular cob to get my thickness that I wanted.# 3, use 1/4" rabbit wire. I built my heat riser with a 16 gal grease barrel and I used a piece of 8" sonitube (round concrete form) then packed a mix of fireclay & pelite around it . The form burned out with the first fire leaving a nice smooth bore for the heat to rise. That system worked perfect , I did a rebuild of my core this summer and simply lifted the 16 gal riser off of the core and moved it a few feet away then set it right back on the new core a little sealant of fireclay & sand and wala ready to go for its second winter.

Thanks!
For #3, you're saying to use the chicken wire, even though you just used a barrel? Doesn't sound like it matters much what i use, and the sheet metal OR the lathe that I already have will work fine.

I just used a 1/4" thick piece of piping that I got from the local metal yard. It's pretty rockin. It'll get hotter than your concrete will. How big was the gap between your heat riser and the outer barrel?

Correct, what you have will work just fine, as long as the insulation is thick enough, you just need to hold it in place . The (matt walker design) riser that I used is such a good method that I like to share it with everybody that will listen ! lol.

Not sure without taking the top off but i'm going to say 2"-3 " The 1/4" metal pipe your using is going to scald out on you before to long and when you rebuild it, look at using matts riser design , it works !

Hmm, well I've been using that steel pipe for 2 winters, and the inside looks pretty tuff still.

John Palombo wrote:Hmm, well I've been using that steel pipe for 2 winters, and the inside looks pretty tuff still.

That means your thing hasn't been rocketing much.

This is after 14 burns, 50 hours may be!



The gas bottle was colapsing under it's own weight when it was white hot! It was part of the heat riser.

That link doesn't work for me, can you check it out please? I'd like to see the state of the barrel

The link works fine for me. Here it is in a public album on Facebook, with another close up of the top of the core. You should be able to see them.
https://www.facebook.com/photo.php?fbid=839281396091080&set=a.522737061078850.127598.100000276815947&type=1&relevant_count=1
https://www.facebook.com/photo.php?fbid=839281442757742&set=a.522737061078850.127598.100000276815947&type=1&relevant_count=1

John, black soot in the riser = no good rocketing.

The barrel image is showing up fine now in the thread. Maybe it just took time to propagate through the web...

I know it hasn't been burning well. That's why I'm expanding the transition bell, as well as the gap between the insulation wall and the inside of the barrel. The gap at the top, between the top of the riser and the top of the barrel, was also about 2 1/2", and I'm thinking of tightening that up a little too.

Hi john ; I shoot for a 2" gap at the top of my riser. Because i am using a 55 gal barrel with a removable top , the top moves up and down as it heats . I measure from the lip of the barrel to get my 2" measurement, when the top is on and the barrel is cold i would have a measurement of 1 3/4 " How thick is your insulation on the riser pipe ? Did you take any temp readings on your barrel top when it was up & running ? With a cast core & riser last winter I was regularly getting barrel top temps of 1050-1100 degree F, this year with a brick core & a cast riser, so far I am only getting temps around 700 degree F at the barrel top, but it hasn't been cold enough to be able to run it long enough to heat it all up yet. I am hoping for similar temps with this core & riser .

John, don't tighten up your gaps. If the thing isn't running properly, that's not the reason. Peter van den Berg has run with up to 4' yes four feet top gap. Enlarging the side gap is good. Below 2 inches, you get into boundary layer friction problems, which will hinder the gas flow. 3cm is the absolute limit where convection doesn't happen anymore (well in roofing, we consider a layer of air of less than 3 cm as still, and therefor insulative) because of the friction on the walls.

By the looks of it, you need to widen your transition area. Most of the well working ones i've seen here or at Donkey's are about a half circle crescent shape, of half the barrel.

I quite like this one.

http://vizbuilt.com/RMH/020.jpg

Or this one

https://permies.com/t/29781/a/12691/thumb-2013-11-18%2015.07.37.jpg

https://permies.com/t/29781/a/12692/thumb-2013-11-18%2015.07.50.jpg



What is your chimney like? How long a run of pipe or what bell ISA do you have?

HTH.

Max.

Thanks! I'll see what I can pull off. My bench/flu is about 25-30' long, and my chimney rises a good 8' above the top of the barrel. I don't know what a bell ISA is.

Well, to explain, a bell is a sort of storage of hot gases, wich are raisig inside, and slowly releasing their heat to the bell material. And it's ISA stand for internal surface area. Which depends on it's architecture, would it be J tube or batch rocket. Single bell or double bell, etc.

But that's not your case.

What is your system size?

This is a quote from Ernie.

Well a 12 inch system will go about 100 feet a ten inch about 75 feet and 8 inch about 50 and a six inch about 45 maximum.

When i read 25 to 30. My idea is, if it's a 6 system, looking at the mass you have around the core, may be 30 is a bit much asking.

Right, so I have an 8" system, and kept my bench around 30'. For the bell, I think what you're talking about is the feed and heat riser, so I've had it as an L tube, the feed 7"x7" square, and the ISA of the heat riser is an 8"x35" steel pipe. The pipe is 1/4" solid steel, so I felt it would be fine with resisting the heat.

I just put a second coat of cement (with a lot of fireclay in it) on this transition area - it will be covered with cob to finish, but it's basically ferrocement in these shots. This is quite a bit deeper than it was last winter - more bubbled out now than slanted directly down into the flue.

The transition area top lip ended up kind of high, so my plan is to cut away the barrel right here to match this shape:
https://dl.dropboxusercontent.com/u/4437344/RocketStoveTransitionArea2.jpg

Here is a better angel that shows more of the over all shape and size of the transition area:
https://dl.dropboxusercontent.com/u/4437344/RocketStoveTransitionArea1.jpg

Once I have the barrel cut to fit just inside the transition lip, I'll cement it over with mostly clay and sand, probably a little Portland, and then pack around it with cob. I think I'm going to shape up the floor of the transition area, where the barrel meats the masonry, with the pearlite/clay mixture. While it's still wet, I'll gently press the barrel into it to indent it. Then I'll complete the insulation for the heat riser, the pearlite/clay mixture contained in 1/4" hardware cloth. I'll keep the top gap around 2"-3" - it does have a removable lid as well - and the side gap around 2" - 2 1/4".

Here it is with the barrel in place, just for kicks. You can see how it used to be just packed with cement where it will now be open, once I cut away the barrel. The clay stain pretty much goes all the way to the bottom lip. So this is the basic shape, but much tighter, that I will cut out of the barrel.
https://dl.dropboxusercontent.com/u/4437344/RocketStoveTransitionArea5.jpg

Well, ISA has nothing to do with the heat riser. It's only for bells, and sometimes is calculated for flues too.

Your system is a 7" system. System size is usualy the diameter. But since friction tends to stall the gases in the corners of a square, so you can say, 7"


Cement is doomed with heat, and with metal inside! I don't know what the clay will do wit it, but i would be affraid to use such a mixture on hot parts.

BTW, metal in the core is doomed too.


Your build is bound to fail.

Sorry to be harsh, but that's the truth.

Another thing, what is the pipe size at the bottom of the transition area?

The piping in the whole system is 8".

John Palombo wrote:The piping in the whole system is 8".

8 inch pipe should be ok.

Are you rebuilding your whole core? If yes and you still use the metal. Put a layer of corugated cardboard around the heat riser, so it doesn't break the mixture you're puting around when expanding, and stays the same shape, only bigger, when the metal finaly burns out.

Some video worth checking.

http://www.youtube.com/watch?v=7RyvsZD1_CU&list=UUnSxSWSpUWwHpr_2WKIF9Xg

Yes, I'm rebuilding the core. If I do what you just suggested, then it will be a 9" pipe, or more, when it all burns out, instead of an 8" pipe. Is that okay?
Thomas Rubino built his whole core out of cement - so it's not doomed?

Satamax Antone wrote:

John Palombo wrote:The piping in the whole system is 8".

8 inch pipe should be ok.

Are you rebuilding your whole core? If yes and you still use the metal. Put a layer of corugated cardboard around the heat riser, so it doesn't break the mixture you're puting around when expanding, and stays the same shape, only bigger, when the metal finaly burns out.

Some video worth checking.

http://www.youtube.com/watch?v=7RyvsZD1_CU&list=UUnSxSWSpUWwHpr_2WKIF9Xg

WOW!!! melt down! looks like the rock wool saved him from unit failure.

looks like yours held up very good Thomas.

Hi John; My original core and my riser are cast from all fireclay, perlite with a small amount of refractory added . My new core is all heavy firebrick with the same riser being reused. I was hoping to cast a core from all high temp refractory cement but time restraints made it faster to build with firebrick. You can see pics of my rebuild under the thread (RMH ,heart transplant )

John, Cement mixture start to spall at 200C°, by 400C°, you have explosive spalling, and at 600C°, chemical bonds fail.

And if you expect to reinforce it with steel, it's even worse, because of the two materials different dilatation coeficients. Steel expanding faster, makes the concrete crack.

If this can be of any interest, here's how i have built my latest core.

All refractory tubing batch rocket. And even this cracks!

http://donkey32.proboards.com/post/11503/thread

Max; I just watched all your videos of the batch rocket wood cook stove retrofit !!! EXCELLENT JOB !!! HMMM .....I have a wood cook stove in our kitchen , maybe ... another project ! Thank you for sharing.