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.
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?
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.).
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.
Before that, I said the same thing about the downdraft you just did
Which part are you exactly talking about?
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.
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.
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.
Inclusion of a P-channel, and a trip wire in the burn tube would be very easy to do regardless of mold material type.
Tim Skufca wrote: I'm not sure what part the "manifold" is
I'd also appreciate a list of items not included in order to construct a rocket-mass heater (aside from all the ducting and the mass, the roof/wall flashing, and the finish material).
Fallon Wilson wrote:Are they able to ship to Canada? And how do I go about ordering one without going to the ATC?
What I am looking for and I think everyone else is looking for also, is written step by step instructions, with well illustrated pictures of every step of construction of what I will call the "burn module" which I would characterize as feedtube, burn chamber, riser, barrel and manifold.
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Rocket Mass Heater Plans: Annex 6" L-shaped Bench - now FREE for a whilehttps://permies.com/wiki/138231/Rocket-Mass-Heater-Plans-Annex