divonbriesen Hatfield

Emerson White wrote:


The more heat you ditch from the top of the barrel the less you have to pay (with draft energy) to force to the bottom of the barrel. This makes it less efficient as a mass heater, but it ensures that it is an efficient combustion device.

Emerson-

So, if we didn't care as much about the mass heat, and wanted more efficient combustion, would it help to put something that could rapidly absorb heat on top of the barrel (i.e. a big pot of cold water, or an aluminum radiator or heat sink)?

I've been trying to use a triple wall stainless steel pipe to serve as both the riser and the outside barrel- for $99 you get the inner (6"?) tube, surrounded by about half an inch of insulation, surrounded by about 1.5" of hollow space. I put an inverted wok over the top, and in my initial experiments at home was able to get what smelled (and breathed) like pure steam out of the bottom. I had trouble replicating this a few days later with a different burn tube.

Some basic math ought to confirm that the outer donut is greater than the inner - if not, that's an obvious issue- but i'm wondering about the dynamics of getting the air up over and back down the outer tube.  Could i just take a cookie tin and use that over the top after bending or cutting the inner flange, which comes up about an inch? Will the supports that hold the outer part on interfere too much with the airflow?

I'm really trying to do this with a minimal amount of masonry - like paul, i want portability, and i'd rather not do anything that involves water or mixing- which means metal, pebbles, ashes, maybe some high-heat caulk.

Also curious about using the lightweight vent stuff for the exhaust- it seems like once we get to the bottom of the outer tube that the temperature will be below 500, so almost any material is safe.

Finally, as I understand it, what rocket stoves are doing is essentially gasification in the 2ndary burn in the torus- is this correct? Is there any way to make sure this is actually happening before going to the next step?

d.i.

ps- was looking at $4 computer fans (80mm size) which are nice and quiet and efficient and could be easily battery powered (12v I think...) - i've seen little gasification stoves that use a battery powered fan- has anyone used a fan to "assist" the rocket? I was thinking that if you had an appropriately sized horizontal inlet to the feed chamber, you could power up the fan for a little boost, to get the flow going (without have to stuff paper down in there, or light a candle, or whatever priming you'd normally do).  We're pretty much going to have some juice at all times in the battery bank, even though it's off grid. I'm still a little hazy on how cool air (in the latter portions of the vent) continues to draw air... it seems like i'd back it up, so you're really pushing it...

velacreations wrote:
don't know if this has been mentioned, but instead of lots of elbows (90 degree turn slow down the exhaust), you need to make some box ends for the pipes.  I can't remember what these are called, but instead of an elbow, it is a big box, so there is considerable volume right there, and you avoid the issues with gasses and lots of 90 degrees.

It is basically like this:
                   ______
--------------|          |
tube                       |
--------------|          |
                  |          |
--------------|          |
tube                       |
--------------|          |
                  |--------|

Does that make sense?

Vela- i believe this is called a plenum.

I was thinking along similar lines. I salvaged some big thick aluminum valves (basically boxes with bit vent doors inside) and was wondering if i could pipe the exhaust in one inlet and out the other since there should be little drag in that big open space, but it should provide a way to dissipate the heat (either to the air, or into bricks i'd put around the box).

icky

Ernie Wisner wrote:

Welcome, Divonbriesen, and good luck with your projects.  i think you'll find most of the proportions you need in the book.  Height is mostly determined by H>L+h, where H is the heat riser, L is the length of the horizontal portion of the burn tunnel, and h is the height of your feed tube.  In practice, most heat risers are 3 feet or more. You can make a large part of this from brick or masonry, but for a portable system a whole barrel is more convenient.

Yours,
Erica

Thanks Erica! That's a great little formula to keep in mind. I've not read the book cover to cover yet, but given some attention to the diagrams, and in particular noted that the burn tube should be the fattest part of the thing. I also saw that it said that the shorter the tube the better- so if the barrel allows, would you ever want to just not have a burn tube at all? I.e. if it was burning right up into the pipe would that be OK?  I was amazed by the performance of my jtube (just two 90 degree pipes put together to make 180) and am curious if the channel is simply needed to get the burn over to the bottom of the chimney.

More questions, but should probably finish book first.

I think between your suggestion of brick and pauls of pebbles and such we can figure something out. My concern is getting a tight enough connection between the pipe and the surrounding material to xfer the heat well... hard to imagine anything bonding like cob- and as paul said, sand will just insulate. Maybe flat plates welded to the exhaust pipe? They could sit on top of and under rows of bricks...

Breh- I'd love to see your plans

Paul- flickr is the world's number one photo site and you should be able to see most all (and all of mine) without any account whatsoever.

Having said that, i just checked, and some of those were listed as private &*(&%$($&*^%($)(32-$!~! - fixed - sorry. Getting used to my new phone, which i've indoctrinated by breaking, twice.

d.i.

Professor-

I'll start by thanking you for your efforts- i cringe when folks say things like, "you clearly don't care enough to" or "don't know enough" or whatever to people they've never met or gotten to know.

For my part I've started playing with these recently- managed to melt an aluminum j-tube in short order, and have now done a handful of brick and metal models- even got in trouble at my own school when a student in our sustainability program said the rocket stove demo was " a good idea" but complained about my lax safety standards. I don't suppose it'll be much help to show them youtube vids with folks working in sandals... sigh...

Anyway, regardless of the naysayers and skeptics, do what you're doing, and share as much as you can, and if you don't want to share it here, share it somewhere else (including to my email di@gdwell.org) . Like Paul, I want to build a portable version, which makes the cob harder to manage. Like you, I would feel more comfortable with a more "precise" plan- worried less about specific costs and more about exactly how many cm such and such an opening should be to get it right - and damn, those 25gal barrels are hard to find- in metal!

Keep it up.

And for the record, I bought the PDF, and the hard-copy - but only after playing around and reading a lot first!

icky

ps- when my first simple rocket stove (aluminum duct jtube inside bigger tube with ashes in middle) melted, a friend watching (who has his own foundry) said, "You know, aluminum melts at 1000 degrees." I asked, "Why the *)(*)U didn't you tell me that while i was building the thing? " He said, "I figure you'll never forget now..."

pps- apologies since this really is the wrong forum- just responding to what's there.

There's a very active conversation about solar thermal heating on simply solar (a yahoo group) - about 600 people, including many who have done extensive work on these sorts of things (mostly the conversation is about solar thermal heating- air and water). It's a yahoo group, which i'm not too fond of, but a great group of people doing great work along these lines.

As far as professor Rich's note about 2% of the need- regardless of the calculations, i suspect the heat generated is a far greater proportion than 2%. The cansolair guy in canada says one unit he sells is good for about 1000sq feet.

icky

Well, this is my first post, and i'm on 3 hours of sleep, so ... well, you know.

I've spent many hours researching this stuff in the wee hours, watched all the vids and read bunches of sites, and somehow managed to still not order the books- not about money... just keep spacing out...

ok, just sent the request to my financier... may order the pdf today, as i'm doing a "workshop" (rather just showing what i've learned and playing) tomorrow for students.

I've so far made a j-tube unit out of regular vent piping. The center tube melted. http://www.flickr.com/photos/divb/5390521505/

I bought a stovetec stove- we'll fire it up tomorrow the first time.
experimented with a couple other things, including some big pipes, ceramics and various kinds of bricks.

I prototyped this in various configurations: http://www.flickr.com/photos/divb/5390476429/



I found paul's think about the portable unit- which is exactly what i need/want for my project: http://ecobox.me - we're in shadow almost all day during the winter, so solar gain sucks-was going to be totally solar, but can't right now. Need some heat: http://www.youtube.com/watch?v=QxsxGT_ZSFY


So... i want to be able to move it in a couple hours, not have messy (or wet stuff) which rules out cob, though i did buy a couple bags of lava rock to play with.

My idea is to build the combustion chamber into this can: http://www.flickr.com/photos/divb/5390578459/

Then use the triple-wall pipe: http://www.flickr.com/photos/divb/5390476429/ as BOTH the draw tube and outer cover- i played with this by putting the wok (see picture) over the top and actually got steam out the bottom that i was able to inhale - no pain, no eye burn (which i'll get immediately in the smoke)... and that was with a pretty crappy way out at the bottom, since it's temporary and i don't want to cut the $100 pipe until i know what i need.

I'm not really clear on the dimensions of burn tube- and am concerned that the metal that holds the outer metal onto the insulated double wall inside will obstruct the flow (sort of 4 "spokes"):  http://www.savemoneywithus.com/images/Img742.jpg

i have a combination of thin heavy firebrick and the thicker very light refractory brick. I need the individual components to be either easily moved by two folks (up and down stairs) or packaged up(i.e. gravel can be bagged, whereas cob is more of headache).

So i've very much got Paul's mission in mind, but far less experience. I also don't mind spending a little to make it work, and would love to have the visible stainless- even thought of putting a big pot over the top and using that as a barrell... but don't know how short i can go before things stop working.

Open to ideas and suggestions. I'd have more pictures of my experiments so far, but they've all been in the middle of the night... as in 2 am, really...

best,

d.i.