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Design proposal for a more efficient, cheaper, and closed loop RMH

 
pollinator
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So I woke up this morning with an idea. Tell me if it sucks..

Rocket mass heaters have a length of duct. Galvanized duct like I've seen a lot of people use releases toxins when heated (not sure if this is practically an issue) and proper chimney pipe is expensive. What if we could eliminate the pipe, keep the heat in the cob longer, shorten the thermal mass, and remove the need for a chimney?

Theory:
I think it can be done by utilizing Tesla valves see this video:



Tesla valves are one-way and slow fluids/gas by creating vortices keeping it in the system longer. Now obviously the Co2 and steam that is exhaust from the RMH out the chimney can't be absorbed by the metal of the duct, but can it be absorbed directly into the thermal mass such as cob? What if instead of a chimney exhausting the Co2 it is fed back into the feed tube (will only flow one way) so it will act like a bellows making the fire hotter but the air will not be moving so fast as to cause a problem.

Or

We can keep the chimney and just use the tesla valve to keep the exhaust in the thermal mass longer but still exhaust it out the chimney.

Or

Maybe the tesla valve can slow the exhaust enough to become the chimney, instead of looping through a thermal mass, build a really insulated chimney and let the exhaust go straight up and out. I doubt this would work as well but could be more compact.


In any scenario the system could compact RMH so it requires less space but half of it would be hotter than usual since the heat distribution is no longer linear.

Construction:
A "cookie cutter" type device can be made to aid in creating an optimal tesla valve by cutting into the cob to reduce the difficulty of creating the shape of the valve. Alternatively metal or cob coated wooden sheets can be placed directly in the cob like in that video's description of the less optimal valve can be done to make a slightly less efficient valve but easier to form.

For cleaning a pipe with a hatch can be placed just before/after the ends of the tesla valve.


Theoretical ProsTheoretical Cons
No expensive/toxic ductHarder to build
No chimney means no permitsPotentially harder to clean
Keeps exhaust (heat) in the system longerSteam may weaken cob
Sequesters Co2Hotter cob surface on half the mass
More compactMore compact



I made some 3D mock ups, the scale isn't great but is a decent visualization. Edit: Now that I look at it the flow/orientation may be backwards, I made them quickly lol.
RMH_TeslaValve.png
Tesla valve cob looping from combustion chamber back into the feed tube.
Tesla valve cob looping from combustion chamber back into the feed tube.
RMH_TeslaValve_2.png
Tesla valve cob from combustion chamber to chimney.
Tesla valve cob from combustion chamber to chimney.
 
T Simpson
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Some kind of tile would have to be put on top of the cob that has the valve carved into it to keep the outer cob layer from falling in the holes; unless you are going with the less efficient sheet method that isn't carved directly into the cob.

I suppose I should make a few more 3D mockups.
 
Rocket Scientist
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Hi T;
This is thinking outside the box!
If you have the time and means to accomplish this for testing, then give it a try!

My opinion is, I don't think it will work.
Here's why)  I think the J tube will quickly stall and start back flowing up the feed tube.
Any fire needs to vent, it will locate the closest, easiest way to do so.

But I could be wrong, after all there's a first time for everything!

To invent you must experiment!  
When you experiment you can have success and you can have failure.
Remember WD 40 failed 39 times before it worked!

Never stop trying!

 
 
T Simpson
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thomas rubino wrote:
My opinion is, I don't think it will work.
Here's why)  I think the J tube will quickly stall and start back flowing up the feed tube.
Any fire needs to vent, it will locate the closest, easiest way to do so.
 



It should be a one-way valve but maybe a gate that can be pulled up after the initial ignition would allow enough pressure to build up in the valve to make sure the feed tube can't force its way backward through the valve.

Of coarse even if this is still a problem we can still try and replace the duct and get the benefits but keep the chimney at the end.



Lots of things to test, the amount of valve segments, the size of valve segments, orientation of segments etc.. Right now I don't really have the resources to be building one of these; maybe in the summer.
 
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A fire needs constant fresh air (oxygen) supply to keep burning. Without some sort of exotic condensing material that can absorb CO2 forever, a closed loop is not possible. What the concept might be good for is creating beneficial turbulence so that the hot gases have as much contact with channel walls as possible. Any fluid will be more likely to flow if its path does not create significant drag.
 
T Simpson
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I wonder what the saturation point of Co2 in cob is before it would compete with the oxygen pulled in by the feed end of the J tube. Perhaps a replaceable filter could be added to increase Co2 saturation.

Maybe a closed loop design isn't feasible but even with an exhaust chimney I think tesla valves can have a big benefit on heat retention in the thermal mass.


What is a good material for Co2 sequestering?  
 
Glenn Herbert
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Cob is not going to absorb a meaningful amount of CO2, if any. It could absorb a certain amount of steam, but that would soften and melt the cob eventually, so is a dangerous idea.

A fire must have a supply of oxygen and fuel, and release a commensurate amount of CO2 and H2O to the atmosphere (or to a big enough sink, which would be completely not cost-effective).
 
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With your orientation of the Tesla valve, wouldn't it be stopping the flow of the exhaust gasses?  Establishing a draft in a RMH is usually important so blocking off the flow seems counterintuitive.  Maybe I'm just misunderstanding your idea though.
 
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I like what you're trying to achieve here, but as others have said, you're applying the Tesla valve in a manner that will only inhibit your gasses from flowing.  This will choke off your draft, causing smokeback and general performance failure.  Perhaps you might consider creating a way for the gasses to take a more circuitous path through the mass?  But one that doesn't inhibit flow.  Honestly, I think it might be hard to find a more practical situation than a well tuned mass bell made into a bench.  But good luck to you.  I have my own dragons to slay.
 
T Simpson
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Mike Haasl wrote:With your orientation of the Tesla valve, wouldn't it be stopping the flow of the exhaust gasses?



If you are referring to the 3D mock ups; maybe. After I made the post I realized I might have flipped one half of the model when I duplicated it making it flow wrong. It still gets the idea across though.
 
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