portable 4" rocket mass heater - The Mass Bucket

There have been a lot of individuals that have expressed interest in a sub-6" system. Either for space concerns, heat output/BTU, or portability.

I think that such a system can be made to work. I know that there are concerns with such issues as draft velocity, laminar restriction, gas friction, etc. Plus, at what point does the idea of down-scaling the principles of an RMH become a moot venture simply because the reduced output of a smaller system would take longer to 'charge' a thermal battery anyway, thereby requiring the same amount of fuel as a slightly larger system.

Bearing all of this in mind, I still think that such a system has merit and that a lot of these perceived limitations could be designed and tinkered out.

I think the first place to start is to re-think the format a bit. Rather than trying to simply design a smaller version of the 55-gallon, two-ton mass, cobbed-in bench style system, the 4" RMH is going to need a different approach-- one that accommodates for the smaller system's shortcomings by reducing its limitations yet still create a robust system that could effectively heat a <500sq.ft. area, maybe slightly larger.

I've been banging this whole concept around in my head for months now... I've gone through good ideas, bad ideas, different sketches, possible solutions, possible failures, built many little J-tube and L-tube stacks and risers in my back yard and fireplace, ranted on and on about Bernoulli, Heisenberg and Venturi to my eight-year-old while driving him to school... and after all of that, I think I have something worth kicking around the table. I finally took the time to put something together in SketchUp so that I can throw it out here and see if it floats .

So far, this project still seems feasible, and I've amassed almost all of the necessary materials, so the first phases of construction are not far off, but I think open discussion is in order before that takes place. Of course, I will document all of the construction here as this moves forward.

In my experimentation with burning in small draft systems, the major issue I noticed with all of them is ash build-up-- smaller CSAs become occluded quite easily. This convinced me that a smaller system is going to require a grate/ashpit of some kind and an effective ash collector.

I also noticed that it is quite easy to choke down a smaller system while trying to get enough fuel into the feed tube to achieve high temps and a good re-burn in the riser and that some type of draft control and/ or draft induction would be needed to ensure proper draft and maintain higher temps.

Now, the main case brought against a 4" system is that it doesn't have the oomph to drive a downdrafted exhaust through a horizontal bench mass to achieve the same efficiency as a typical 6" system. Well then, here's my solution: quit expecting too much from a 4" system-- decrease its mass load, decrease its horizontal run and give up a bit on the efficiency side of the equation. Look at it this way... if the typical answer to a small footprint/small space/lower output problem is a 'pocket rocket', which is much less efficient than an 'average' RMH (if there is such a thing:)), then there has to be some middle ground.

First off, let me say that I just got my hands on SketchUp, so I'm no master and some of the more subtle details are not hashed out in this model, but this is good enough to get the main ideas across.


I have a 16" x 22" steel civil defence issue water barrel that is the intended container for the project. Everything in the barrel will be cast inside of a mix of fireclay, alumina fibers, sharp sand, and perlite. I've test fired this material and it comes out light and hard. I have no real idea at this point what the final mass will be, but I'd be willing to shoot in the ballpark of <100lbs. The parts that are to be the feed tube, burn tunnel, coal pit, and lower part of the riser, will be made from a cardboard form that, after it is cast into the system, will be burned out before the actual heat riser is installed. The heat riser will be made of alumina/fireclay mache wrapped around a piece of sched.40 steel pipe that may, or may not, burn out, while everything else will be steel 4" duct. You can see that the feed tube and the burn tunnel have been rotated 45 degrees: this is so the system is somewhat self-cleaning. Ashes and embers fall into the coal pit where they are allowed to burn completely before sifting into the ash box which will have a removable drawer for easy cleaning during operation. There will be a cover of some kind on the ash drawer to control the bottom-draft. The radiant exchange will be a section of 8" single wall black stove pipe with an endcap. The exhaust chimney will be a 6' section of double-wall classB gas vent.

Here's a detail of the intended function:



Questions? Comments? WTFs? All are welcome.

Interesting design...might want to consider something heavier (oxy/acetylene tank or similar) for the upper radiant "barrel", and perhaps you could clarify - is the lower barrel "full' of insulating refractory? I don't understand the junction between "barrel" and exhaust.

A heavier section top "barrel" could also be augmented with some added fins or pipes to assist in heat dissipation.

Another approach might be to extend your assembly vertically, imagine another barrel acting as mass/bell under what you have drawn...yeah, I know...endless possibilities!

Also check out this guy's work: http://www.youtube.com/user/tryin2lhard/videos

Nice concept, you've got us all thinking; I'm working on going with smaller CSA's too, hope to post some pics soon

Andor

Andor Horvath wrote:Interesting design...might want to consider something heavier (oxy/acetylene tank or similar) for the upper radiant "barrel"

While that would give it longevity, and a bit more thermal transfer (although I think surface area would be quicker multiplier-- I've thought of using a piece of 10" stove pipe, but then I would have to have an offset riser and, it begins to get too close to the feed tube opening and, I would possibly have to incorporate a heat shield of some kind, which wouldn't be the end of the world), but I guess one of the running themes with this project is portability so, the lighter the better. Also, as I mentioned before, this is not what I would consider a refined rendering of the intended design-- I'm considering having the junction of the 8" pipe to the cast material be gasketed such that pipe can be removed and replaced when necessary. The structural steel channel that is the ash box/grate for the coal pit, is also removable for replacment when it burns out.

and perhaps you could clarify - is the lower barrel "full' of insulating refractory?

Yes. 3:1:1:9 -- fireclay:alumina fiber:sharp sand:perlite

I don't understand the junction between "barrel" and exhaust.

Which?

The squeejaw way the elbow exits the barrel? As far as the angle at which the elbow exits, once again, not a perfect drawing. For the most part, it's proportionally correct, but not what I would call positionally correct. Things like...

...the ductwork on the bottom (which I might do with 4" flexible exhaust tubing, the automotive kind, instead of 4 elbows-- not only for a smoother path for the gases, but to be able to line up with the side of the barrel exactly and not have to cut some eccentric opening. I will probably also use a more serviceable joint at the exit of the barrel-- like a class B snap-loc),

...or the way the gases transition from the bottom of the upper "barrel" into the ducting through the lower barrel (this will be much less clumsy than it appears as I will be cutting and bending a 10"x4" 'register box' to create a much better junction),

...or the distance to which the stove pipe "barrel" extends into the cast material (this will be much shorter)

...or the way the feed tube has the just slightest taper towards the opening (this is just the way SketchUp warped the tube when I 'rotated' the end to get the bias-- I'm sure there is a much better way to do this, but it was the intuitive solution at the time. In reality, I'm actually considering making the feed tube portion of the form be shaped on top of a firebrick split so that the opening will have a flat bottom and a round top, kinda like a train tunnel. This will not only give the feed tube greater durability, it will be a better flow transition at the coal pit)

...all of these things need to be hashed out in a new drawing. As before: this is just to get the initial idea across...I'll be posting a revision soon.

Or the T-junction? (which is what I think you are referring to) The tee will have an endcap on the bottom and is intended as a fly-ash/condensate catcher and clean-out.

A heavier section top "barrel" could also be augmented with some added fins or pipes to assist in heat dissipation.

[Now you've got me thinking;)] That's actually an excellent idea to add to this design and I already have visions of cutting aluminium channel dancing through my head. I'm gonna have to find somebody with a drill press and a bandsaw that I can use...

Another approach might be to extend your assembly vertically, imagine another barrel acting as mass/bell under what you have drawn

While that is entirely possible, since I do have two of these old CD water barrels, and each one has a nice recessed lip on the bottom that fits perfectly into the lid of the other for easy stacking...I promised the person that gave me these that if the first stove works, I would make him a second one in the other barrel. I mean, these are pretty cool. They both still have the complete paint-stamped "Civil Defense Department" instructions on the side for how to use it to store and dispense drinking water...or use it as a commode ;P The real cherry-on-the-cake subtle irony with these is that they were manufactured by Rheem!

...yeah, I know...endless possibilities!

True! While scrounging at a local place that has a lot of smaller sized steel barrels, I did see a malt syrup barrel that was the 14"x35" size (22gal?) ...tall and narrow... it would be a bit of a squeeze at the top with a 'V-tube' style rocket, but it might work.

...oh, I'm gonna be spending a lot of time on SketchUp...

Also check out this guy's work: http://www.youtube.com/user/tryin2lhard/videos

I have, and I would have to say that that there are a few other similar 'radiant bell, no mass' designs that I have seen, but another critical point to this project is to have a self-contained, radiant-mass system that will still deliver heat after the fire has gone out. The other plus to this design is give the unit a better 'safety zone' by essentially having the stove be the mass and giving it a slower dissipation rate. It remains to be seen what kind of burn time/heat retention/hot spot dynamics it will have...it may be a smaller system, but I do expect it to burn quite nicely. ...and, not to be a broken record, but: portability.

Nice concept, you've got us all thinking; I'm working on going with smaller CSA's too, hope to post some pics soon

Thanks, Andor. The sharing of ideas always moves things along faster than the mulling of ideas ;). I hope to see your pics soon.

Chris

Nice pants.

I have two of these barrels. I like your design.

Andor Horvath wrote:
A heavier section top "barrel" could also be augmented with some added fins or pipes to assist in heat dissipation.

maybe something like this?

...oh, were it only that I could afford 24' of 4"x1" aluminium channel

I understand the register adaptor now.

Just downloaded Sketchup too, and trying to get my head around it; used to jockey Cadkey and Autocad a little. Seems everyone has to have their own methods/commands/short cut keys!

Fins/pipe: my approach - whatever's best bang for the buck, whatever you can add for enhanced surface area as "fins", or pipe/angle to induce convection flows.

Have you found, or would you consider posting, models on 3D Warehouse?

Might wanna review Clarry, Zaug, Wiseway and kimberly soves for ideas...perhaps seperate the heat/combustion from the mass section, kindof a modular approach?

Got my own head spinning now!

Andor

Chris et al,

here's an interesting way to do it (portable, mass, rocket), just make sure you have the correct type of (non exploding) rocks...actually, pretty do-able

http://www.tamizsolutions.com/2012/09/10/the-rock-bucket-rocket/

...more idea fodder

andor

Andor Horvath wrote:Chris et al,

here's an interesting way to do it (portable, mass, rocket), just make sure you have the correct type of (non exploding) rocks...actually, pretty do-able

http://www.tamizsolutions.com/2012/09/10/the-rock-bucket-rocket/

...more idea fodder

andor

very interesting...I like the simplicity of the idea, if not the rustic antiquity.

however, I wonder how much of the smoke is actually burned off as opposed to how much is 'filtered' by the rocks. if the ones on the top are covered with that much soot, then it would seem that not all of the smoke is actually being consumed by fire. yes, the exhaust cleans up and becomes clear, but with all the carbon deposits on the rocks closest to the top of the riser, I wonder how much CO and methane made it out alive.

still like it, though...you could definitely scale it up into something like a low-brow masonry heater-- big brick box full of rocks with a firebox... say that three times fast;)

Andor Horvath wrote:Chris et al,

here's an interesting way to do it (portable, mass, rocket), just make sure you have the correct type of (non exploding) rocks...actually, pretty do-able

http://www.tamizsolutions.com/2012/09/10/the-rock-bucket-rocket/

...more idea fodder

andor

The stove in this link is something my mind has been toying with the past few days. I think by adding a J tube it would increase the efficiency, also maybe increasing the size of the exhaust tube. He also could try a P-Channel to increase the rocket effect and efficiency. This is a good start for a portable unit and a shop heater. The trouble with rocks is that you can't use thin walled tube with out taking a chance of crushing them with the weight of the rocks.

I am looking at the photo and thinking of the fins;

Those whirly vents on top of barns, can never remember the names of them, maybe grab the top whirling part and pop it on top, see how much heat it radiates before creating one of the fancy fined jobs first. Just a thought, it is cheap and every scrap yard as well as perhaps every farmer might have a few older non workers kicking around.

For the top part the person who stated use the Oxy Acetylene tubes hit it right on the mark, me thinks. Those are nice and heavy duty, will hold heat like cast iron and last a good long time. if you want a shorter version, there are some smaller ones as well. Might want to look at a truck wrecking yard. The air tanks on the big trucks are good sized as well as good steel, even the old rusty ones can be cleaned up easy enough and give good returns. Additionally there are easy to plug holes all over them that might accommodate some piping that you can run water pipe through to heat up water. just a though or two.

I am wondering if you set a wind turbine on top of the barrel if the heat would make it spin?

I sort of meant it would radiate the heat. Unless the center post is still there it will not spin at all. You could probably rig something up at the top, so that it could sit there to be able to spin.
Dude, now you got me thinking it might be cool to see if it does or not, hmmm great idea!

Chris, I like the idea of a rocket core with all the essential 'plumbing' - just add a barrel and riser and hook up the exhaust. But instead of using cardboard forms, how about paper maché?

You could sculpt the internals in negative - creating the perfect angles, smooth curves, etc., then make a mold of plaster (or resin or whatever). From the mold halves (or as many pieces as you needed to cut it into) you could lay in paper maché. Once dry trim and paper maché the partials together to form a perfect sacrificial form to pour your refractory mix around. Keep your molds and it is easily repeatable.

this guy casted the removable portion , would have to change the feed...

http://www.backyardmetalcasting.com/bucketfurnace1.html

...oh, were it only that I could afford 24' of 4"x1" aluminium channel

Since this is for radiance, you need not go with such heavy stock. Aluminum trim coil (from roofing supplier) is a good material which is easy to work with. It is heavy enough guage to allow for good rigidity, yet easily bent. L shaped bends of 1" x 4" are easily done with a homemade break. The heat is conducted through the fin and radiated to the surrounding air about the same as heavier stock.

Andor Horvath wrote:Interesting design...might want to consider something heavier (oxy/acetylene tank or similar) for the upper radiant "barrel", and perhaps you could clarify - is the lower barrel "full' of insulating refractory? I don't understand the junction between "barrel" and exhaust.

A heavier section top "barrel" could also be augmented with some added fins or pipes to assist in heat dissipation.

Another approach might be to extend your assembly vertically, imagine another barrel acting as mass/bell under what you have drawn...yeah, I know...endless possibilities!

Also check out this guy's work: http://www.youtube.com/user/tryin2lhard/videos

Nice concept, you've got us all thinking; I'm working on going with smaller CSA's too, hope to post some pics soon

Andor

Holy Crap! I just talked to that guy (tryin2hard)! He rocks. He has some great new ideas that incorporate the bernoulli principle/venturi effect.

i agree- he designed my latest pellet burner- which is a jet style with secondary air- designed around bernoulli and ventury effects. he said he wants to see my new T2H designed jet burner and i plan on public sharing when i complete the pellet feed