Use of ceramic glass in a batch box roof to preheat secondary air in a batch box.

Pyro's.

I'm contemplating using ceramic glass to form the roof of a batch box as a means of porting heated secondary air to the riser throat.

The plan is to have one sheet of ceramic glass as the ceiling of the batch box and use say, 1 inch of ceramic fiber board around the perimeter of the glass panel and then top it off with a sheet of ceramic fiber (or other suitable material) in order to create an air gap with a path through the system from the door to the riser throat.
If used in a Double Shoebox type setup, two panes of ceramic glass could be used so as to capture heat from the secondary as well as the primary firebox.

The working idea here is to capture as much of the early startup heat as possible and get the air in the airgap warming up as soon as possible to help fuel the secondary burn.  You might wonder why I would want to have the secondary air entering the system so much farther up from the port, (I can see Peter scowling at me  now) but the system I have in mind will be using a space resembling that of a cyclone separator in order to capture the hottest gases in a circular path that encourages turbulence through the use of (trip wires) on the ceiling of the chamber ring.  As the gasses expand and cool, they will spiral downward to the bottom of the cone, dropping their load of ash and particulates in the collection chamber at the bottom.  Once gases have reached the bottom of this cyclonic secondary chamber, they will spiral back up into the inside tube and make their way to the back end of the system, oven, bench, cooktop, radiant bell/drum, or with the use of dampers, maybe more than one.

I propose building the firebox and what I will call the Combustion Cyclone out of a aerated (foamed) mix of castable refractory cement, bulk ceramic fiber, and pearlite.  I expect to use some ceramic paper product with which to form the inside tube for the Combustion Cyclone.  Sodium Silicate will be used on the ceramic paper as it is rolled into form on a 8 inch diameter tube.  (8 inches as this is the size of the system I am targeting.)

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I have followed the adventures of a certain Honey Do Carpenter on Youtube who has made a name for himself with his experiments in foamed Portland cement.  Seeing his success in that endeavor gives me confidence that same can be achieved to some degree with the 60% alumina castable refractory I have available.  This video shows how his aerated cement can be poured into panels. https://www.youtube.com/watch?v=MXs-tqfCSX0  
Such an aerated mixture could also be easily poured into molds to create more complex forms.

This is where you guys get to pick this apart and ask me questions about things I have overlooked.

It's high time I started this build, so I think I will start with the bench, that will give me time to get these other details sorted out.  I'll probably keep documenting this build here so if any of this intrigues you, then please follow along.

A diagram of how a cyclonic separator works.  Notice how the entrance leads into a circular path that crashes back into itself.  Also, since there are no moving parts, the entire form, with the exception of the exhaust port tube, can consist of negative space.

This is an interesting concept. Lots of people have designed explicitly circular vortex-generating combustion cores, but I don't recall one intended for ash collection as a major function. Have you built or used a standard rocket mass heater, either J-tube or batch box? Are you aware of the fly ash generation rate? RMHs typically need cleaning of fly ash downstream of the firebox/burn tunnel maybe once a year, so I wonder how important the cyclone is for that.

A major function of the heat riser is to keep the gases super hot until they finish combusting, and to generate draft by the principle of hot gases rising; I wonder how much draft this type of cyclone would generate. If you have a strongly drafting chimney, the combustion core does not need to provide the draft, but if not, you would want as much draft from the riser as you could get.

A cyclone to separate ash would depend on smooth flow so that heavier particles could settle out, which is at odds with the principle of turbulent flow for gas mixing.

Hi Glenn,

Nice to hear from you.   First of all, thank you for your input.  

I have not as yet built a standard J-tube or Batch rocket, this would be my first.  Although I have studied these boards and the material at Donkey's board for several years now, so I have a pretty good understanding how things are supposed to work.

I was not clear on how often the fly ash would need to be collected, once a year doesn't sound bad, but once every 5 or ten years sounds even better if the cyclone proves efficient.

My situation affords me a 34 foot chimney, mostly sheltered from the outside.  It provides good draft so I anticipate that it, working in tandem with the push generated by the batch box, will provide sufficient throughput to get the hot gasses through to the bench where I will have a bypass installed for quickly heating up the flue.

If you look at the cyclone drawing, you'll see that the mixing will take place at the top, as the gasses spiral down, they eventually are pushed to the bottom where they then vortex their way back up the inside tube and exit.  I've pondered how hot gasses would work in such as system v.s. room temperature gas, but it shouldn't matter, since all of the gas should remain close to the same temperature in this highly insulated enclosure.  I imagine adding (tripwires) if I am remembering correctly the way a ripple, or bump, was provided in the ceiling brick of a J-tube burn tunnel to promote mixing.  As of yet I have not landed on a particular plan for that.
As for the particles settling out, that is what the lower 3/4 of the cyclone is for.  I expect to have to find a way to mold this so the cone is very smooth.  Casting a block with a traffic cone has come to mind.

I spent some time last night chasing down parts to build the foam generator.  Here is a video by Jim White which shows how such a foam generator is built.  Jim has provided further links about how it works.  https://www.youtube.com/watch?v=P5EMmo4XNQk

Of course I'll be doing some testing on this foamed refractory cement before I commit to casting large parts.

Any advice you may have regarding the pitfalls of such a foamed refractory or the use of the ceramic glass in the burn chamber would be much appreciated.  Other threads seem to indicate the ceramic glass can handle a great deal of heat.  Probably even better if it has a constant flow of air over it to help keep it cool.   Others have hinted at mixing ceramic or other fibers and or pearlite in with the castable refractory though I have not seen the results of those experiments.
To be sure, I am not aware of anyone attempting to use a foaming agent to expand the castable refractory so I am out on my own in that regard.  Though hopefully, not entirely out in the weeds.

It sounds like you won't have to worry about draft
An 8" batch box is a beast - what sort of space are you looking to heat? 6" is the most common size for a batch box that I have seen.

If you want to experiment to find improvements on the tried and true, I think it would be very beneficial to test a standard design first so you can tell whether the more complex experimental design is worthwhile. A J-tube core is easy to make up and test, and if you use clay slip mortar, all the parts can easily be reused in another setup. A batch box can be connected to any kind of riser, so you could make  the firebox and test it with different risers, a standard style and your cyclone. A 5-minute riser (1" ceramic fiber blanket inside a sheetmetal tube) could be reused in or on top of a cyclone if you want to. Are you thinking of the cyclone cylinder being 8" diameter? Given the desired flow path, I think it would need to be distinctly larger to not be a bottleneck, say about 12". 8" would be appropriate if you only wanted the gases to spiral up.

As far as smoothness in the cyclone, I have seen others here who have investigated and found that no matter what, ash will accumulate on surfaces and cause some roughness, so beyond using generally smooth forms I don't think you would benefit from special measures in that regard.

I have a 2000 sq ft basement to heat.  But I am open to downsizing things if practicality points in that direction.  While you are probably being a good friend and doing me a kindness to try to talk me out of it, there are three innovations I wish to explore with this build.  Yes, I could go with a tried and true method, but being a tinkerer at heart, there wouldn't be nearly as much fun in that.  I stuck my head in the old fireplace today and removed what was left of the broken flue damper, so I guess you could say its officially started. Got a nice shower of soot and cinders all over my head to show for it too! I didn't measure it yet but the flue opening appears to be about 4 x 16 inches.  Just about perfect csa for an 8" core.  I've decided to build my bench and core foundation utilizing a bed of insulating perlite and whatever binder makes the most sense, and an assortment of solid concrete blocks.  Cost is about 4 cents per pound/ 72 dollars per ton.  Like you suggest, I will use a clay slip to bond them together.  My backyard consists almost entirely of dark gray clay that should work well for that.  Right now I can get my hands on everything I need except for that ceramic glass.  Put a shout out to my local FB group for unwanted electric glass topped stoves.  I'm sure one will make itself available to me in due time.  For now I'll be working on assembling that foam generator to make the expanded castable and making some observations about how well that chimney draws.   Wish I had a sketch or two to help illustrate my plans.  I've tried using sketchup but found it all rather frustrating.  I'm fantastic with conceptual visualization....putting visual ideas on paper?  Not so much.

Oversizing a mass heater is not the same problem as oversizing a wood stove - if it is more powerful than you need you can just burn less often, as long as the core and mass are properly sized to each other and to the chimney. An oversized wood stove is dangerous as it invites frequent throttling and heavy creosote generation with risk of chimney fires.

I think some clarity about the elements you will use and their relationship would be helpful. You plan a batch box; that is straightforward with the port location to be decided. Batch box dimensions have been thoroughly tested and the best proportions are given at batchrocket.eu. The question is how you will go from the firebox to your cyclone. The cyclone wants its supply horizontal at the top of the cylinder. This works with the standard port and with the sidewinder port, but the double shoebox does not seem to have a neat direct connection to the cyclone.

"but the double shoebox does not seem to have a neat direct connection to the cyclone."

But what if we turned the upper shoebox 90 degrees so it exhausts perpendicular to the core?

A word of warning here regarding the chimney size. It might be that the csa of the chimney looks like it's perfect for an 8" system. In my opinion it isn't, due to aerodynamic behaviour in that same channel. The hot and fast streaming core will be quite narrow and the corners aren't helping a strong draft, rather the opposite.

In this part of Western Europe the chimney sweeps are using a century-old formula to determine what diameter a comparable round channel would be.
It goes as follows: take twice the width, multiplied by the length of the chimney's csa and divide that by the sum of the width and length. The result is the diameter of the equivalent round duct.

2xWxL / (W+L) = D

Conclusion would be: your chimney is comparable with a round duct of 6.4", aerodynamically-wise.
An 8" system-by-the-book won't run well on such a chimney size. Let alone coupled to a cyclone which gobbles up a substantial part of the draft energy anyway.

I had assumed that the 4" X 16" was merely the throat opening, leading to a squarish chimney. If the whole chimney is 4x16, that is very different as Peter says. If this is an urban party wall brick building, a wide thin chimney is likely; if freestanding, I would think a square chimney would be more likely. You will need to determine the actual situation before proceeding.

Let me elaborate a bit further.  the chimney itself is at least 8 inch CSA, but the flue opening in the old fireplace, which is a 1950's style manufactured insert known as a Heatilator, is approx 4 x 16 inches.  I have wondered about how restrictive this might be and it would be easy enough, though with some discomfort, to take a cutoff wheel to it and make it larger by 3 or 3 times what it is now.  That would open up access to the full throat of the chimney opening above the smoke shelf.  That would minimize any restriction at that point.  I was curious about sealing off the hearth and mounting a small anemometer in an opening to measure draft.  Do you think that would be worthwhile.  

Glenn also made a point about the diameter of the cyclone.  Just in keeping with the 8 inch box plan,  then the inside, vertical exhaust tube and the exhaust opening of the cyclone would have a CSA of 8 inches.  The diameter of the intake and main cyclone cylinder would be proportionately larger, though I feel there is room to play with here as the gasses can descend to a lower point in the cyclone as long as the output side provides room for equilibrium. The cyclone combustion chambers I have seen others attempt always permit the hot gasses to flow freely upwards.  This one restricts their upward movement for a given time until they reach the inside exhaust tube where they then are free to ascent and exit.  I like Peter's idea of going smaller on the core and leaving room for back end restrictions, however they might be useful.

Now that you've got me thinking about it, I am uncertain of exactly what the dimensions of my flue tiles are.  They are terra cotta flue tiles with a square profile.  To be honest, I have always assumed they are 8x8x 24, which is common around here, but I could be wrong, they could be bigger, though I doubt they are smaller.  I guess that wins me a trip up to the roof to get the numbers.  There are 3 flues in my chimney.  One of which is used for the main fireplace upstairs which we enjoy often.  The second is the one to the old heatilator, which I will use for this build, and there is a third, which I believe was built into the system as a means of providing make-up air.  A system which as popular at the time but proved to not be very effective or efficient.

I'll be back with my findings.  It will be much warmer here in NW Ohio next week so I will wait until then as to avoid any icy roof accidents.

I haven't found flue tile smaller than 8" x 8" nominal, so I expect yours are at least that size. The ones I have are around 7" x 7" inside. (Tiles from two sources have slightly different dimensions.) 10" x 10" is the next larger square size.

Weather here is optimal so I jumped on a ladder and got up on the roof.  Unfortunately, I am unable to get as close to the chimney top as I'd hoped.  My chimney has a hardware cloth rodent screen with 1/2 inch square mesh so I was able to count the squares and come to a pretty close estimate.  I was wrong about the form though, it is 12" x 8" rectangular.  So I would suppose that still leaves me in a good position.  I also lit a small fire in the old fireplace today, seeing as how the broken flue is no longer in the way, the draw was instant and impressive.  No worries there. I'll have to find something to block it off with in the meantime while I'm building or I'll be heating the great outdoors.

I remember Glenn had said something regarding the cyclone about ash building up on surfaces no matter how well you try to polish them.  I don't suppose it's all that important, so long as those loose agglomerations of ash are able to break away under their own weight from time to time and fall to the bottom.  Probably all the better that way.

Ok.  I would like to report some progress on this project.  As I mentioned earlier in the thread, one of my objectives is to experiment with aerated refractory cement.  To do that I would need a foam generator.  I just finished that up tonight, perhaps tomorrow I will get a chance to leak test it and check it for function.  Next up is the miniature propane furnace for heat testing the aerated refractory mixes.  Very interested in doing a test on aerated geopolymer, but I'm not confident in my chemistry ability and not sure how to go about that.  Any suggestions in that regard would be welcome.

https://drive.google.com/file/d/1N4Vn5i8vn-QAd9Z1vpiciENXkKs7nk2m/view?usp=sharing

As usual, nothing ever happens on any kind of schedule I can imagine, but...I have made some progress.  Since I last posted I learned a great deal about geopolymers and their value to us as stove building refractory, as well as other building uses.  I have also been studying an old patent I discovered online.  Patent 3,944,425  from back in 1976.  In it are explained a number of different recipes for making a foamed ceramic refractory with little more than some basic ceramic supplies and a mixing paddle.  Here's a link to the patent.  I'll be having a go with example number 34, as I'm hopeful that my backyard clay will make a fair stand in for the fine grained brick clay that is called for.  Patent 3,944,425

Well,  I've been having a go at proving out the recipe #34 from the aforementioned patent for foamed clay refractory materials.  Unfortunately, it would appear something is awry.  Desiring to use my local clay instead of a powdered clay, I may have introduced an undesirable variable to the process.  Only now after four experimental batches am I getting anywhere near to a mix that will set up.  The formula calls for approximately 5 percent Calcium Aluminate cement, but I am now up to nearly 40% cement and still have not obtained a material that will set up enough within a few hours that can withstand being handled.  This latest batch "might" get there after 24 hours.  I'll know in the morning after I check after I sleep tonight.  Maybe some ceramicist could tell me if there is something about leaving clay in a super-hydrated state as in a slurry that could cause it to not want to bond with cement?  The foaming aspect of the recipe does seem to be working, but having to add this much cement is greatly diminishing the appeal as the objective of the process is to be able to obtain a high performance refractory product at low cost.  At any rate, I will determine how much cement it takes to make this mix firm up and fire a few pieces.  Then I will obtain some powdered clay and attempt the recipe again as written.

Edit.  Got home and was delighted to see that the castings had set up, so I went ahead and risked demolding them.  They came out quite well.  Here's a picture of what they look like just after putting them in the mold. webpage
And here's after demolding and trimming.  The green clay body is still very carvable.

Now it's time to put these in a fire and see what happens next.  Remember, these bricks are formed from:
500 gm Clay Slurry. At 1.30s.g.
Calcium Aluminum cement 200 gm,
Talc 25 gm
Calcium Carbonate 10gm
22ml Aluminum Sulfate solution.

The idea is that the calcium carbonate and the aluminum sulfate react and create millions of tiny bubbles of co2 gas that become entrained in the mix.  According to the patent, the bubbles are on the nanometer scale so most of them are invisible to the eye.  The bubbles are supposed to help provide insulation, and the clay and aluminum combine when fired to create a foamed ceramic refractory.

Success!

Following morning it was raining so I put one of the four samples in the fireplace and built a fire in an attempt to fire it.  Have to decide on forge or furnace to do hotter tests.

Weight before firing: 147.3 gm.
Length before firing 98 mm.

Impatient.  Once the coaling phase was diminishing. Removed it from coals and let it sit in a pile of wood ashes to cool.

Weight after firing: 82.9 gm.  44% water content when fired.
Length after firing: 95 mm. Indicates 1.3% shrinkage.

Observations:  There do appear to be some cracks in the test brick, but even after some physical  manipulation and stressing, the block keeps it's shape and doesn't crumble.  Further firings will attest to it's durability.  I took a flat bladed screwdriver and scratched at the block and found that it was rather easy to make scratches in it, though not deep.  The material feels a bit like a piece of chalk.  Brick is approx 5.25 cubic inches.  15.79 gm per cubic inch.
Ultimately would weigh approximately 60 lbs per cubic foot.   There is no doubt that the material does insulate, as I held this flame on that spot for over a minute and then was able to let the opposite side of the piece lay directly on my bare hand immediately afterwards.
I know a propane torch isn't much of a torture test, but it's the best I can do at the moment.  I'm very interested in building some sort of a DIY foundry so I can get up to some really good temps and use some pyrometric cones to ascertain what kind of temps these materials can withstand.

Thanks for the update. I am eager to see your progress in geopolymers.

The google drive photo of your foam generator is visible to me - looks great, can you give a breakdown of the build?

But for the recent photos of the fired brick I do not have access. It requires me to ask for access, which I could do if that were necessary, but maybe there is a setting on your end to make them visible like the first one.

Thank you for the feedback B.  I poked around and found a setting that should allow anyone with the link to view the file.

My foam generator was inspired by Jim White on youtube. https://www.youtube.com/watch?v=P5EMmo4XNQk

I made several changes from his in an attempt to increase the capacity and to tidy things up a bit.  Watch the video and you'll understand how mine works as well.  One thing I might change is to eliminate the air pressure being introduced into the reservoir and allow atmospheric pressure to "push" the foam concentrate into the eductor at the "Tee".  This reservoir cap does not seal well and although the setup works fabulously, I don't know if a pressurized reservoir is necessary.

Access to the pics should now be open to everyone.  Sorry about that.

Today I think I learned what was wrong with my clay slip that required so much more cement than what the recipe called for.  The patent author stated that the mixture should be about the consistency of a "Deflocculated clay slip."  Not being familiar with the term, deflocculated,  I ignored it at my own peril.  After taking a deep dive into the subject, I now understand that adding a deflocculant to the mix will enable the clay slip to flow better.  In essence, it causes the electrical potential in the clay particles to repel each other.  Not having used a deflocculant, I simply watered my clay down to a workable consistency, thereby requiring the use of more cement.

I also learned that our trusty friend, Sodium Silicate, is one of the most commonly used deflocculants.  Next to that, Sodium Carbonate (Washing Soda).   Interestingly enough, when Sodium Carbonate is used, the carbonate binds with calcium ions which are plentiful in clay, forming Calcium Carbonate, which combines with the Aluminum Sulphate solution in making the millions of insulative CO2 bubbles.  Who knows, depending on one's clay, one might even be able to omit the addition of Calcium Carbonate powder from the mix entirely.

Looks like I'll need to go back to the workbench, deflocculate my clay slip, and try this again.

Thank you for posting your updates, it is interesting to see what you are trying to achieve.
In your mind are there any benefits with making your DIY foam cement mix over buying a commercial insulating refractory mix?
It is the cost or improved performance ?

Hi Scots,  You are very welcome.  "Is there any benefit over commercial insulating refractory mix?"  Well, for one thing, that stuff is expensive.  The recipe I am currently working with calls for 87% clay.  Which I can dig up out of my back yard, a small amount of talc, some calcium carbonate powder, and some Aluminum Sulphate.  All cheap as dirt.  (pun intended), The most expensive ingredient, Calcium Aluminate Cement, is $30 for ten pounds and the recipe only calls for 5% cement.  I'd call that a bargain.  Will it hold up as well as commercial stuff?  I don't know.  We'll find out. But it's certainly a lot cheaper.  Had the wife pick up a box of Arm and Hammer Washing Soda today to use as a deflocculant.  Hopefully this week I'll get a chance to work out just how much of that I need to add to my clay slip to get the best effect. If that works out and I can get my cement content down to even 10% I'll be very pleased.  I'll be attempting a number of things over the coming weeks and months so stay tuned.  Next on my list after perfecting the batch via deflocculants is a DIY foundry to do torture tests on test bricks.

In the U.K. I can find insulating 1200c mix for around £30 for a 25kg bag or £35 for 1400c .
I like your ideas based around a cyclone vortex, that concept is used in both marine aquariums and Koi pond filtration units.
I have seen double glass used to feed air in Foxfish videos so it can be done successfully.
The issues I see might be the overall height of the fire box and if the  lower part is actually needed ?
I really like the ideas of the top part of your diagram but in any case I look forward to seeing how your ideas develop.

Heating secondary combustion air is energy intensive robbing heat from the system, in my opinion providing excess combustion air better serves your end means.

Cyclone separator is going to rob or more correctly add to much friction for the system to perform correctly. It greatly diminishes volicity that which drops ash.

Joe Danielek wrote:Heating secondary combustion air is energy intensive robbing heat from the system, in my opinion providing excess combustion air better serves your end means.

Cyclone separator is going to rob or more correctly add to much friction for the system to perform correctly. It greatly diminishes volicity that which drops ash.

I wonder if what you are saying really matters ?
Some people might just enjoy carrying out their ideas regardless if it is not an already tried and tested design or perhaps the glass feed ideas looks nice and that is more important than ultimate performance?
I love to read about folks interesting ideas and their journey to see how it comes out.

I wonder if what you are saying really matters ?
Some people might just enjoy carrying out their ideas regardless if it is not an already tried and tested design or perhaps the glass feed ideas looks nice and that is more important than ultimate performance?
I love to read about folks interesting ideas and their journey to see how it comes out.

As long as one accepts failure as a positive to build on.

In answer to Scots remarks about economy, I did some shopping around and about the best I can do for a castable insulating refractory, on a cubic ft comparative basis, is a product called insulcast, which would cost me 93 dollars for one cubic foot of finished product.  My clay recipe, should the defloculation prove effective, should yield a cubic foot for about 60 dollars.  Considering most builds aren't going to require that many cubic feet of castable insulation, it's probably not worth it from that standpoint.  But I don't tinker because I'm trying to save a buck.  I love the journey.  A question leads to an answer, which leads to a what if? which leads to more questions.  This is how I play.  I am imaginative, intuitive and resouceful.  It is my way.

Jo,

One of the three experimental legs of this adventure is the use of ceramic glass in the ceiling of the combustion chamber as a means of eliminating all metal from the combustion chamber.  I'll beg to differ with you about secondary air robbing the system of energy, I don't see how heating secondary air or suppling an over abundance of primary air would make any difference to how much energy was required to heat that air.  With a secondary air setup we are introducing the air at a strategic location, 100% primary air, as you suggest, is all introduced at the same location.  I will build my stove door so I can cut off the secondary air and feed it all from the bottom.  I really like the idea of having a 1/2 inch slot on the floor of the combustion chamber that allows the ash to fall through into a pan and the primary air volume is controlled via a vent on the end of the pan where the door seals against the stove.  Alternatively, a cleanout door with a vent on it.  I have seen these available commercially.

Regarding the cyclonic separation of ash in what I am now calling the "Inverted" or "Two-Phase" riser, if it happens, great, if it doesn't, no biggie, that aspect isn't a deal breaker for me.  It's the idea of containing the combustion gases at the top of the outer cylinder and holding them there until they work their way down to the opening of the inner cylinder, up and out that most attracts me.  I'll still put a cleanout in the bottom of that chamber for cleaning and to introduce a camera into it so I can see what's going on in there.  Friction will be relative to the amount of space the gases have to circulate in.  I don't see how my riser will generate any more friction than a straight vertical one that is twice as tall.

Obtained a burner for DIY a forge/foundry.  Set up a propane tank, some bricks and whatnot to hold the burner and the sample brick in place.  Let it burn for about a half hour.  Edges glowed red.  No difference to the material afterwards.  Though I suspect it was all much hotter when it was baking in the coals in my fireplace.

I won't be doing any more tests on the original bricks.  I'll be saving that effort for the next batch with the deflocculant.  In the meantime I'm waiting for my clay slip to settle out so I can pour off the excess water and get it back to a specific gravity of 1.75 to 1.80.

Well I would say that depends on your definition of failure?
Lots of people, probably thousands, are very happy to use their less than optimum rockets stoves?
If you build a device that satisfies your needs how can that be failure?
Don’t get me wrong as I am also extremely interested in progress and development to obtain the best possible function it’s just that I don’t see any issues with folk doing their own thing especially if it is fun.
.

Thomas Tipton wrote:

Jo,

one of the three experimental legs of this adventure is the use of ceramic glass in the ceiling of the combustion chamber as a means of eliminating all metal from the combustion chamber.  I'll beg to differ with you about secondary air robbing the system of energy, I don't see how heating secondary air or supply an over abundance of primary air would make any difference to how much energy was required to heat that air.  With a secondary air setup we are introducing the air at a strategic location, 100% primary air, as you suggest, is all introduced at the same location.  I will build my stove door so I can cut off the secondary air and feed it all from the bottom.  I really like the idea of having a 1/2 inch slot on the floor of the combustion chamber that allows the ash to fall through into a pan and the primary air volume is controlled via a vent on the end of the pan where the door seals against the stove.  Alternatively, a cleanout door with a vent on it.  I have seen these available commercially.

Regarding the cyclonic separation of ash in what I am now calling the "Inverted" or "Two-Phase" riser, if it happens, great, if it doesn't, no biggie, that aspect isn't a deal breaker for me.  It's the idea of containing the combustion gases at the top of the outer cylinder and holding them there until they work their way down to the opening of the inner cylinder, up and out that most attracts me.  I'll still put a cleanout in the bottom of that chamber for cleaning and to introduce a camera into it so I can see what's going on in there.  Friction will be relative to the amount of space the gases have to circulate in.  I don't see how my riser will generate any more friction than a straight vertical one that .

In my book failure is a positive as it becomes a known.

Striving for a complete burn by insulating this and that to concentrate the heat in the burn tunnel and riser yet introducing secondary combustion air at a lower temperature down stream defeats that goal by cooling down the 'combusting' mixture. Been there done that, it takes up to 40% (average 20) of your primary flame energy to pre heat secondary combustion air to a reasonable temperature to not diminish the temperature of the primary flame. The industry already went there. Costs for energy for preheating run 30 to 60% higher. What the industry opted for is not 'over feeding fuel' in conjunction with assuring 'excess' combustion air is introduced that is more efficient and fuel wise. To me in a RMH excess combustion introduction is done one way - not over feeding the feed tube: feeding fuel at a rate that complements the system.

Cyclone ash separator is going to act like a close blast gate - dead heading the exhaust stream stopping all inertia in my opinion. Will be interesting to see. Jo is a females name, my moms - thank you.

Joe

"Jo is a females name, my moms - thank you."

My apologies Joe.  Honest mistake.

BTW, your argument against the secondary air aspect of this build is giving me great reason for pause.  It would eliminate a good deal of complexity from the build, as well as not requiring as much height in the combustion chamber, which equates to a longer inner cylinder in the cyclone chamber.  Coming up with a metal free secondary air design was a personal challenge I had set myself, but if you are correct, and I believe you very may well be, keeping it simple would be all that much better.  I will definitely keep this in mind.  There is a lot to do before I commit to a core design.

Took Jo as a compliment. ~(:-{ )+<

Lol.  My kindest regards to your Mother.

I wasn't going to do any more testing with the old bricks but a friend offered the use of their oxy-acetylene torch.  How could I refuse?  But first, here is a picture of a brick being heated by my propane forge burner.  It's glowy, but nothing it can't handle.

Then the real fun begins after hitting it for several seconds with the oxy torch.  The operator told me he did not attempt to use the steel cutting aspect of the torch, as that most certainly would have obliterated the sample, but it obviously got pretty hot.  I was very surprised the sample did not spall or break apart.  Instead, it held it's ground while taking the punishment and remained stable with the exception of partially melting in the intense heat.  After allowing the sample to cool, the blackened, vitrified part feels very smooth and glassy to the touch.  

For those following this meandering hodgepodge of ideas, I have had an interesting development.  My past efforts in replicating recipe # 34 in Patent 3,944,425 were failing due to variables that I had inserted into the mix.  After taking some time away from this project to work on others, I gathered some dry clay from my backyard diggin's,  a second hand cooking pot, a baseball bat, some kitchen sieves, and our old food processor that never gets used anymore.  After beating the clay down in the pot, sieving it and running it through the food processor, I was left with a sample of very fine powdered clay with which I set to work making another batch of recipe #34.  I combined all the all the dry ingredients and mixed them well.  I then mixed in the water.  The last step was to add the aluminum sulfate solution and begin mixing with the immersion blender.

Again I was disappointed as the patent states that the mixture should be firm within an hour, but mine wasn't even close, but considering that I wasn't using a verified "Powdered Brick Clay" as the recipe specified, nor was I using the "Lumnite Calcium Aluminate" cement, I decided to wait it out to see if time was a variable that might act in my favor.  Despite this shortcoming, the mixture was markedly more liquid than the mixtures I had made with the wet clay slip, which makes me believe that thixotropicity (the propensity for some clays to exhibit gel like characteristics when allowed to sit in a hydrated state" is coming into play here,

On the second day the sample still seemed very soft, but on the third day the sample was firm.  I was very hesitant to demold it right away, but opted to chance it.  The brick dislodged from the mold very well and felt "leather hard" as those who work with clay might say.  I measured the sample for length and weight, and despite having a fire going outside I decided not to attempt firing it right away as I have done with other samples, as I would rather find an opportunity to have it fired in a real kiln at much higher temperatures.  

So anyway, to sum things up, by working with dry, powdered clay, I was able to get the cement ratio down to where it should be at approximately 5% of the dry ingredients which I feel is very economical.

Following this experiment, while I allow that brick to dry and await a proper firing, I decided to do another experiment with the wet clay. (I still feel working with wet clay might have it's advantages as you can skip a lot of the labor in processing it.)

I mixed 200 grams of clay slip at 1.51sp with 20 grams of cement, and the other ingredients as a double batch.  To this I added about a cup of wet Fuller's Earth. (not the powdered kind, the kind that looks more like kitty litter and is used as an oil/spill absorbent).  Being that Fuller's Earth is classified as a refractory material, I felt this would be a good material to use as an aggregate to further stretch the clay foam mixture.  Adding the Fuller's Earth effectively quadrupled the volume of the mixture and at 20 grams, gives me the same economy as the brick made with the dry clay.  Fuller's Earth is about $10 for a 40 lb. bag.  This batch just happened to be enough to fill all four cavities in my mold, so now I wait.

I would be interested to hear from anyone who would be willing to let one of my experimental bricks "reside" in your batch box over the next heating season.  I am interested to discover how the material survives over time in an environment that is much hotter than the one my fireplace can provide.  The bricks are only about 1"x1"x 3.75" so they wouldn't take up much space.