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Rocket Mass Heater Shippable Core  RSS feed

 
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Hi everybody.

Len, the enlargement of the transition between barrel and flue comes from two factors, the first flow shape change. The gases all going down "vaguely "evenly in the barrel tore, then being pushed to one side to exhaust the barrel. And the subsequent laminar flow drag created by that movement. And the laminar flow drag created in the elbow. Elbows, you most certainly know that, create turbulence of the flow, creating ripples and waves on the inside bend of the elbow, partly blocking the flow, slowing it down. And another thing, you can reduce the csa of the flue, at some points, like going through a wall. It will impede with the flow somewhat, but not that much. Even more if you manage to make it like a proper venturi, having the top profile of a plane wing inwards.

Paul and Jesse, the core looks nice, but to the the exhaust transition looks too small. Tho, that's gut feeling.
 
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I know the barrel and manifold are positioned where they are in the design because the goal is to try and bring the gases as far down as possible before they enter the thermal mass.

This is extremely valuable when trying to reach a low bench mass but I wonder if focusing on that aspect is necessary at this stage of research?
With the pebble system the mass box is long and short, like a bench, why not a different shape? More mass would be required by a box of larger volume but then more mass would improve performance right? So now instead of this low box perhaps a counter level "crate" of mass. In this application you could start way low to bring the gases in near the floor but is there a major benefit to doing so? Perhaps bringing the gases out of the burn a bit higher off the ground would simplify the design?


Picture this: the mass "crate" is built, the core, parts etc are packed in it. The crate is shipped, arrives, gets unpacked, assembled, mass is added final flue connections made and the PRMH is done. Sure there may be applications where a low drop or "zero clearance" manifold might be needed or would perform better but perhaps to launch the shippable core / PRMH that isn't as necessary.

What do you think?
 
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Satamax Antone wrote:Hi everybody.

Len, the enlargement of the transition between barrel and flue comes from two factors, the first flow shape change. The gases all going down "vaguely "evenly in the barrel tore, then being pushed to one side to exhaust the barrel. And the subsequent laminar flow drag created by that movement. And the laminar flow drag created in the elbow. Elbows, you most certainly know that, create turbulence of the flow, creating ripples and waves on the inside bend of the elbow, partly blocking the flow, slowing it down. And another thing, you can reduce the csa of the flue, at some points, like going through a wall. It will impede with the flow somewhat, but not that much. Even more if you manage to make it like a proper venturi, having the top profile of a plane wing inwards.

Paul and Jesse, the core looks nice, but to the the exhaust transition looks too small. Tho, that's gut feeling.



Basically this is really hard to model. Also it is different in different builds. I only have experience with my own build and would have to speak from that the flue gas coming out at the manifold is not going that fast, I would question how much laminar flow effects things. I agree that the turn would affect things, but I have found that I can cut the CSA in half almost right out of the barrel without effecting the RMH operation. However, my RMH is a not cob model and I have used a thin insulating layer on the riser.... So I had 5 inches clearance from the riser to the barrel wall even with the riser centered (6 inch system BTW) and the gas did not have to change direction till it was all the way at the bottom of the barrel which in my case was actually an inch or two lower than the burn tunnel. So the exit flue had close to 270 degree access (out of 360... this is not temperature) from the gas. It the core above it looks to me like there is only about 100 degree access or a little more.

There were some other differences in my build too. I had mass all the way up the barrel and on top as well (somewhere around 600 to 800 pounds) which would have cooled the gases faster than an open barrel (some may disagree). And the manifold area was not insulated at all being bare metal. My bench is a low bell which even though only four feet long, cools the flue gas enough that it will exhaust through a four inch flue (from a 6 inch riser) with no change in rocket effect from a 6 inch flue. Also, I do not intake my air from the top of the feed, but rather at the bottom of the burn tunnel. My feed is sealed. This means I get much more affect than the three foot high riser would indicate (it may be an inch or two lower in fact).

The big difference I see between this shippable core and the original site build, is that the site build manifold tended to be more of a funnel shaped while the shippable core is a circle on the surface of the cylinder section. For an 8 inch system, I would actually recommend making the exit hole 10 inch or even 12 inch followed by an adapter to bring it back down to 8 inches to give back the funnel effect in the original design. Then I think the shape shown in the sketchup would work fine. I think even if the adapter was one of the step shaped ones it would be fine, but I use a short funnel shaped one (I go from six inch to five inch at the manifold).

One has to remember that the RMH as we know it is a compromise design. The feed is as high as it is for less burn attention required even though it makes problems down the line. It is built of mainly found materials which may not be the very best too. This may be a good thing sometimes too. If the flue gas gets too hot the amount of NOX will rise as well... again compromise, get the best carbon burn without oxidizing the nitrogen in the air.
 
Len Ovens
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Mike Leo wrote:I know the barrel and manifold are positioned where they are in the design because the goal is to try and bring the gases as far down as possible before they enter the thermal mass.

What do you think?



I am not sure what to think. I could see there being a market for a smaller foot print mass heat storage as it has been mentioned more than once. The reason for the exhaust from the barrel is not just to get the pipe low enough to work with a bench, but rather (or so the theory goes, I don't know what testing has been done with higher exit points) because the flue gas cools as it falls becoming more dense and heavier thus helping to pull more flue gas through the riser, tunnel and feed. This has been called the "pump action" that helps push the flue gas all through the mass. The reason I say "I don't know what to think" is because so much of the thought around the RMH is theory. I could list a number of things I wonder if anyone has tried, each one of us only has so much time or money and when things work well we tend to think we have arrived and don't go farther. I would like to know, for example, how the ratio of mass to insulation in the riser affects thing... in a numerical sense. So there would be thickness of the wall, "R" value of the wall and mass of the wall. Then how do these things affect the riser temperature the barrel flow rate, the amount of heat the barrel surface puts out. How does mass on the barrel effect things? Again, there are variables such as denseness of the mass as well as just thickness. The main reason against mass on the out side of the barrel has been that it may crack from temperature differences from top to bottom or that the top needs to be able to radiate for the pump to work right and recently there are questions about the longevity of the barrel top if it is not able to stay (relatively) cool.

All that aside, I think your idea of a smaller foot print, taller mass is a great idea. I would still like to feed it as low as possible because I believe it would give the most comfortable heat. Keep my feet warm and I am warm. Lots of truck drivers keep the heat on around their feet but have the window open for fresh air. A half door with the bottom closed and the top open is nice even in cooler weather. The old Russian peasant stoves were up on massive wood blocks so they could be cooked in (at least before the early 1900s) and they had to use external heaters down low to feel comfortable. Then someone set it up so the flue gas went down under the oven into mass at floor level before going up the flue. A huge step forward.
 
Mike Leo
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Len it sounds like you also would enjoy a blue sky budget and research staff lol.
I often imagine what we could do with even a meager "corporate research budget" in this space.


Erica did chime with this (and a lot more, of course) on this thread
The relevant excerpt is:

Erica Wisner wrote:If you are not trying to force the rocket exhaust through a long, low heat-exchanger, you may be able to skip the downdraft bell.
Shedding heat from the barrel is how we get the exhaust gases down low enough to go through a seating bench located near the floor. If you can build your rocket lower than the boiler, and don't need to lower the exhaust as it enters the boiler, you don't need the downdraft for this application.
(In a few instances where someone wanted to use masonry or cover the barrel in cob, a short bench and a tall exit chimney can compensate for the loss of the barrel's heat-shedding downdraft function. In that case it becomes more like a contraflow stove.).



Before that, I said the same thing about the downdraft you just did
 
Len Ovens
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Mike Leo wrote:Len it sounds like you also would enjoy a blue sky budget and research staff lol.
I often imagine what we could do with even a meager "corporate research budget" in this space.



Hmmm, Yes and no. Paul is doing that, and while I don't control the research, things are happening. The biggest problem is that I can't afford to help finance what he is doing. Everything I would send him would just set me back in moving forward with my own project. I know that sounds selfish, but my project is my own family and I only have one chance at it. So I have to make sure of that first. I think this has a lot to do with the speed of research in these things. People scratch their own itch and it is amazing to me how much has been done as each person tries something different.


Before that, I said the same thing about the downdraft you just did



Ya, we have all read the same books and the same threads What started out as a poor man's masonry heater, has taken on a life of it's own. As we take the RMH into more esoteric places, it may get to a point where the masonry heater becomes the poor man's RMH. This could be really true of the single skin unit built with adobe bricks. I do think it is a mistake to think of the RMH as apart from masonry heaters. There has been centuries of research done on masonry heaters, much of it seat of the pants heat for one family based on what a friend down the road has done. It would be a mistake (in my opinion) to ignore all of that.
 
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Hello, I had an idea that Id like to have considered here. I think that for the manifold portion of the shippable core, metal should be tried. A steel cylinder would certainly weigh less than an equivalent concrete, cob, or ceramic one. Also from a function standpoint, it would I think serve as an extension of the barrel in cooling the gasses, and maintaining or increasing the strong downdraft. I'd love to see this tried and I'm not likely to get to it as quick as some of you folks might, as I haven't started my first rmh yet. Please let me know any pro or con thoughts on this.
 
Satamax Antone
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gary kanitz wrote: Hello, I had an idea that Id like to have considered here. I think that for the manifold portion of the shippable core, metal should be tried. A steel cylinder would certainly weigh less than an equivalent concrete, cob, or ceramic one. Also from a function standpoint, it would I think serve as an extension of the barrel in cooling the gasses, and maintaining or increasing the strong downdraft. I'd love to see this tried and I'm not likely to get to it as quick as some of you folks might, as I haven't started my first rmh yet. Please let me know any pro or con thoughts on this.

Which part are you exactly talking about?
 
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If you count left to right in this image for the core, the third itteration has the outer cylindrical portion of the manifold shown offset as a seperate piece. That piece is what I would propose should be metal, so that it contiues the function of the barrel itself (removing heat from the exhaust and increasing gas density) down lower. I think any heat acumulating in a casting at this point would weaken the gas flow out into the horizontal portion of the flue where it enters the thermal mass.
newshippableidea.jpg
[Thumbnail for newshippableidea.jpg]
 
gary kanitz
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Also, is anyone building/ testing the core idea in that pic yet?
 
Len Ovens
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gary kanitz wrote:If you count left to right in this image for the core, the third itteration has the outer cylindrical portion of the manifold shown offset as a seperate piece. That piece is what I would propose should be metal, so that it contiues the function of the barrel itself (removing heat from the exhaust and increasing gas density) down lower. I think any heat acumulating in a casting at this point would weaken the gas flow out into the horizontal portion of the flue where it enters the thermal mass.



I agree about the using metal part for sure. My reasons are probably different but that is ok.

- It would mean the interface from the top barrel to the bottom is close to machined and easier to seal.
- The core is meant to be covered with cob anyway so it doesn't matter if it is steel or not.
- There would only be one clay/cob/brick to steel seal transition.
- The weak point at the tunnel to manifold would be eliminated.
- The cost goes down if this can be made from a barrel.
- - It is cheaper to ship.
- - Or it is easier to make a spec for that can be made locally at any machine shop and avoiding shipping.
- There is no problem with heat wearing out the steel at this point as things are relatively cool.
- It can have a bottom and clean out built in. Easier to clean out without lifting barrel, or easier to latch to barrel for easier detach/lifting.
- It may make certification/permit acceptance easier.
- Because it is thinner, the clearance from the riser to the barrel and the space for gas to pass is bigger making for easier manifold design.
- It would allow for a higher barrel and therefore riser.

As a side point, I feel that an open barrel detracts from the whole mass idea and that the bare to covered ratio is more to do with responsiveness/user comfort than helping gas flow... though I would suggest mass against the barrel be more dense and not insulating so that it continues to sink heat away from it (I would not use cob or cob brick near the top).

Also with a steel lower barrel, I would make the exhaust bigger CSA than the riser and convert it back down after that inside the cob. These converters/adapters are not that costly anyway. I guess the first stove pipe could modified by hand too. Overlapping the sheet metal more at the exit end.

Once this part is made separately anyway, a steel bottom barrel could be tried with no rework of the rest of things.
 
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Lots of knowledge getting tossed around here. I'm learning lots.
 
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I want to throw the idea of creating a shippable mold out. The freight savings would be more than enough to cover the cost of sending a reproducible mold out the door to each customer. Customers would probably use the thing more than once, spreading the technology. Could also offer to send molds with a return label for a rental fee.
 
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Len Ovens wrote:

John Adamz wrote:I've read extensive discussions about the size of the manifold area here and on the donkey proboards (research by Peterburg), and the conclusion was that it needed to start at least 2x the CSA of the core. So for an 8" core it should be in excess of 100"sq. It also seems that by creating a venturi effect with the manifold the smoother (edges/corners) the transition from the gasses around the barrel/riser to the exhaust duct the better.
I think Jesse Biggs current system is an excellent example of that principle.



I wouldn't quite put it that way... The pipe leaving the manifold is 1x the riser CSA. So it should be possible to have the area going down to that being 1x. The reason it generally isn't has to do with the geometry. The CSA that matters is right at the point where the outlet meets the manifold. The space from the outlet to the outside of the riser/burn tunnel is quite narrow and so for constant CSA that gap needs to go all the way around the outlet, but can't because of the bottom of the manifold is at the same height as the outlet. So the CSA has to be measured using just the top of the outlet. Also, even though the outlet is mostly round, for CSA measurements it needs to be treated as square mostly (some open tank bottom ends circumference works), in other words an 8 inch pipe cannot be measured as .5 of circumference for calculating CSA, it is closer to just 8 inches. If the manifold was to be built below the burn tunnel with an open space in front of the outlet, then the area feeding that space could be 1x CSA of the riser.

In other words the flue path must be at least 1x riser CSA all the way and in most cases (assuming cob manifold) the CSA feeding the manifold area has to be much bigger in order for the feed to outlet to make that 1x riser CSA. Lifting the outlet up 4 inches or so from the bottom of the manifold space may make a difference too as it unblankets (is that a word?) the bottom half of the outlet.

It is certainly a hard area to get right.



This is a good summary of the manifold constraints.

I usually abbreviate it this way:
- If your manifold is roughly a cylinder, with the duct entering a side wall, the heat riser and firebox in the center are an obstacle to flow. Also, the flow is mostly entering the top half of the pipe, not flowing equally from all sides.
Therefore, you want about double the gap in front of it compared to the heat riser gap. On an 8" system, that gap is about 2" for the heat riser, so I want about 4" between duct opening and obstructing walls inside the manifold. Anything less than a 2" gap will definitely affect performance, unless steps are taken to open out this shape as the funnel and taper advocates suggest.
- If your manifold is more like a box with a slot in it, that slot needs to be at least as big as the CSA of the rest of the system. 2 or 3 times the CSA seems to work even better, from practical experience.

- All of these minimum flow areas described above need to remain adequate, even while fly ash settles out like snow on the bottom of the manifold. Raising the pipe up a few inches above the bottom is helpful. Using a vertical drop instead of a horizontal slot is helpful.
Making too many direction changes is not helpful - the fly ash tends to accumulate on any ledge-like structure.

I consider a manifold well-designed if the system performs well through at least a full heating season, and includes a cleanout access to remove fly ash annually (usually just before the start of the heating season, or just at the end.)
Ianto likes to include a deep ash-pit that reduces cleaning to every 5 to 7 years. I find it difficult to remember how many years it's been, after about 2 years, so annual cleaning may be an easier pattern to manage.

I do not find it particularly necessary to smooth the surfaces of this transition. While there may be short-term benefits for a test system, for a full heating season I don't think it matters much at all.
There will always be some turbulence in the transition from a larger to a smaller space at right angles to each other. The fly ash settles in corners with low flow, so the main flow channels will carve themselves somewhat over time. The fly ash can also settle as fluff along the walls, even sometimes sticking to the metal barrel. Unless the walls are smooth enough that ash and soot cannot stick to them, any smoothing is temporary.

I do like to include a distinct, sturdy transition at the edges of the walls, using tile or plaster or chickenwire, so that it's easy to know where to stop cleaning. Perlite-clay, fiber blanket, and other insulation materials are soft, can be easily confused with fly ash while cleaning, and can be sucked loose or damaged by a hard vacuum nozzle.

-Erica W
 
Bill Puckett
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I originally posted this back in February but some kind of glitch arose so only I could view the comment. Trying again...

Thank you all who posted such great information above. After thinking about my shippable mold idea here is what I've come up with:

Package and send four pieces of rectangular plywood sufficient to create a four sided box. Include eight right angle metal brackets to hold it together (two for each corner). Also send a flat rectangular piece of light gauge sheet metal with which to create a cylinder, and three bands to wrap around it. Also send instructions.

The customer will assemble the box on the site of the install so no form floor is required. The box is two feet tall. The customer takes three straight pieces an elbow and a T of ducting they have on hand and makes a feed tube, closed bottom T to burn tunnel, elbowing to heat riser. This is placed in the box on a few support rocks so that the top of the feed tube is flush with the top of the box (the heat riser section is at least a couple feet above the top of the box). This ducting is the interior form for the core. Next, the customer uses the included sheet metal and bands to form a cylinder and places it directly over the heat riser duct, so that one side is resting on the duct which is the top of the burn tunnel. This cylinder is the exterior form for the heat riser, and is a tad lower than the interior form to enable sculping of the ash shedding slope. This can all be kept upright by laying some pieces of wood across the box and sticking something in between the interior and exterior heat riser form so it doesn't skew. Then the customer fills the box with an appropriate material they've purchased. Then the customer fills the heat riser form with an appropriate insulative material they've also purchased. After a short time the customer lifts the heat riser form to the top of the box so that it is easy to remove after it cures. Minimal mixing will occur.

The top of the box is the bottom of the manifold. While curing, the customer sets the barrel in an inch or two at various times to form the barrel seat. The customer cuts an upside down U-shape in the bottom of the barrel to connect the mass ducting to.

I don't know exactly how to solve the uneven thermal expansion problem, but think previous poster John Adamz is probably on to something. In this design there are two materials, but they gel to form one piece. Would the sacrificial inner form ducting create a separate thermal expansion problem? I don't know. Another thread arrived at the conclusion that this was ok to use (in the riser anyway).

As for competitiveness, this product would cost somewhere around $40 in materials, and shipping would run about $40. With $70 profit that's $150. The customer is likely to spend $100 on material they would not otherwise have to buy if they were purchasing a shippable core, so the total customer cost for the core would be about $250. It's quite simple, and everything can be used over and over again. The cheapest dragon heater core is $350 on their website as of today, not sure if that includes shipping. I think this product is very competitive and possibly game changing.

The bracket supply could be eliminated by dadoing a groove in the end pieces of plywood for the side pieces to fit in and advising the customer to put something heavy up against the ends to support them. Or supply a rigid insulation box form with floor, again advising the heavy objects for support on the outside. The increased cost would be offset by lower shipping expense and the insulation would probably be useful to the customer, maybe as an underlayment for the mass.

I would like to try an RMH with no cleanouts except at the vertical transition (for wayward critters). The alternative I'm thinking of involves a shop-vac. Use it to vacuum the feed tube, then reverse suction to blow it out every once in a while.

Now for the depressing stuff. It occurs to me that someone selling this product would be taking on unacceptable product safety liability exposure. If anything went wrong, lawsuit. Also, since the RMH is not really legal, just sending it to someone at an urban address could turn a judge against you. Then there is the possibility that someone drops $150 on the product, builds it inadequately, and sues you for their day job. I think I understand why Paul doesn't want to be in this business.

On the bright side, it is a quick, inexpensive way to put the tricky parts of an RMH together, and now it's public knowledge. And since it's fairly inexpensive, someone could develop very specific instructions, follow them several times, and have the resulting heaters tested by UL. Then maybe it would be marketable. It would definitely be a step toward more wide acceptance.
 
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Bill P, nice idea. Ship the molds, critical parts, durable instruction books, dvd, (access to youtube) parts list and dimensions, and code approved tie-ins to chimneys or fireplace. After I do my build I can use the molds and instructions to help my neighbor, brother-in-law, etc to do their build.
 
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Just a quick FYI. The $350 price for Dragon Heaters includes the fabricated steel feed tube and heat riser. If someone wanted to buy just the burn tunnel, the price would only be $140. The steel feed tube which is cooled by 2ndary air prevents a secondary chimney from forming.
 
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Bill Puckett-
I read this a couple days ago, but just now have time to post a reply. I really like your ideas. You have thought through the whole process of a mass sale of a RMH core. I like the idea of a reusable core mold pattern, but think as a complete core/manifold it might be difficult to achieve.

I would like offer a slight tweak to your plan. Since the outer box of the core is nothing anyone couldn't make skip shipping that and focus on the burn core. Either send the core mold pieces precut and ready to put together (very small package) or maybe an already assembled core mold. This main core piece I don't see any way to reuse/rent :edit: I just thought of a way to do this easily but using words is not easy so I'll try to learn to use sketchup and create a visualization.

Since the manifold is also a desired part of this shippable core project I suggest one of the simplest methods is to use expanding foam sealer and fill a mold (Jesse Biggs AWESOME manifold design would be a great template) then cut the molded pattern into smaller pieces for shipping. Perhaps some kind of durable coating to make it reusable. More involved solutions are an actually manufactured pattern of other materials like ABS or other molded plastics is an option if setup cost of such a manufacture can be amortized. These methods could also be used for the burn core mold itself.
All of this is predicated on the notion that the end user is going to cast the core themselves using a supplied formula for a refractory mortar mix.

2 more design points. 1-It is my understanding that using round ducting for the mold (as well as a 90deg elbow on either end of the burn tube) is not as desirable as a square burn tube design which creates the turbulence required to create maximum efficient combustion. Inclusion of a P-channel, and a trip wire in the burn tube would be very easy to do regardless of mold material type.
2- I have this 1 problem with most RMH designs. That is the lack of a feed tube ash pit and ease of cleaning ash from the feed and burn tubes.
If you burn any quantity of sub par wood as I frequently do (since I have a HUGE source of it) you can very quickly clog the burn tube with ash and coals. A very simple solution is to make an ash pit in the bottom of the feed tube of 2 1/2" (thickness of a full fire brick), then have a "door" (a full fire brick on it's side, or ?) on the bottom front of the feed tube that can be opened/removed for EASY cleaning with a regular ash shovel.

I am getting really excited about seeing this project to fruition. All the great ideas put forward on this thread are adding to that excitement.
Even though the heating season is nearing an end (at least hopefully here in SW MO) it isn't slowing me down.
 
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Inclusion of a P-channel, and a trip wire in the burn tube would be very easy to do regardless of mold material type.



One problem with this, is that these design points are covered by a patent filed. Any commercial attempt to duplicate these design features would be pursued.
 
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a summary of shippable core stuff from the 4-dvd set "better wood heat: DIY rocket mass heaters"

 
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