Peter van den Berg

sara ventura wrote:First questions raised by these drawings:

-Can the depth of the portal be 6.4cm? And the height of the riser 105cm instead of 108? 6.4 is the width of my firebricks.

Yes, the port could be deeper than suggested, so 6.4 cm won't be a problem. The riser could be anything between 10B and 8B. Shorter isn't recommended. Top gap, above the riser, AT LEAST the chimney's diameter. More is better.

sara ventura wrote:-Between the back of the firebox and the back wall of the stove I have left 21cm( x 61cm width). Is that enough?

This should be enough by itself, but there's another opening, at the right side of the firebox. Together they provide plenty of space. It is important that the gases are able to stream under the firebox, and from there to the chimney.

sara ventura wrote:-Would it make sense to draw the riser on the left, place the exit pipe on the right corner and have a much shorter lever for the bypass?

It would make sense, although not for the bypass. The door is further away from the wall as a left-hand sidewinder, I would see that as an advantage. Thought: you are building a 1st generation batchrocket. Provided there is an adequate chimney, this model doesn't need a bypass. So, what will the chimney be like?

sara ventura wrote:-Is 3 or 2 cm space enough to leave between the pipe and the internal walls? The exit pipe will have an angle as it is because of the thickness of the wall of the stove,    so I may well place it wherever I want.

This internal chimney pipe should be insulated somehow, otherwise the heater's exhaust gases will be higher and efficiency would be quite a bit lower. Insulating of the pipe could be done with 1" superwool around it, fixed to the pipe with chicken wire.
Another thought: since your chimney pipe is in a corner, about half of the opening won't be used by the downward streaming gases that need to go through a 180 degree change of direction. Stream profile should be about twice the chimney's cross section area, in order to avoid friction spots. Calculating... that internal pipe should be at least 15 cm from the floor, assuming afor-mentioned pipe is shoved in the corner of the bell.

sara ventura wrote:-If I rise the core with a metal structure, would a vitcas paint coating 1750º/3180º or similar be ok to protect it and the wires to reinforce the riser and core?

Of course you could use that Vitcas coating. But I doubt it will be necessary, because during the running-in period the heater will produce quite some soot. All the cold steel inside will be quitely coated with a layer of wood tar, no corrosion expected. It escapes me what you mean with wires to reinforce the heater core?

Yet another thought: the top of the bell should be double-walled (bricks on edge), with thin (1/2") superwool between it. See the Mallorca or the Brussels build. The reason for this is that the top of the bell will get hottest during the burn and the bricks will expand because of that. The inner skin will be able to expand in the above construction, without pushing the outer skin apart.

Leonardo Bevilacqua wrote:I have a question though. I was examining your sketchup model of the door. In your model you built the airframe with a 60x60x3 mm square pipe, which has an internal section of 54x54mm which is 2916 mm2.   If I follow the instruction on the page you sent, this section should be 15% of the chimney pipe section. The chimney pipe section for a 150mm system is 17671,5 mm2, and it's 15% would be 2650mm2, not 2916 mm2. I don't understand why measurements don't match. What am I getting wrong? This is only one example, but also the main slot opening doesn't match the requirements. Am I calculating something wrong? Or, should I just use your model, scale it up 1.2 times to match my 180mm system, and copy your measurements?

If you are aiming for 15% of the chimney's cross section area, that would mean there aren't any square or rectangular tubing that are exactly that size. So, what you should do is searching for a size that is close to what you want, preferably a little bit larger, not smaller.
As you may be aware of, the air supply is only just large enough, it isn't  the limiting factor during the burn, the internal proportions of the core are. During development I had the air inlet on anything between 30% and 45%, it turns out the 30% figure is enough and not too skimpy.

The measurements are what to aim for, the model is the result of the aim.

Hi Matt, I was waiting and expecting for somebody bolting an oven to the reversed Shorty core, and you did. A white oven like yours is probably less complicated as compared to a black one, I realized while I was viewing your pictures.

The deviation from the airframe design might play up when the core is really, really hot. The air box as the lower door frame member means that the air, going through two changes of direction could pose a friction point for the air stream. Maybe you could widen the intake opening even more, so that the air streaming doesn't need to make sharp bends. That the air intake is larger doesn't make any difference, the proportions of the core are the limiting factor, combustion-wise.

In my design, the air box under the door is also functioning as a threshold, so the ash won't fall out when the door is opened. And in a recent implementation I added a tiny slit high in the inside of the air box, and it appeared to be working as a boost when the core need to heated up. The slit is thin as a normal cutting disk, and only 4" wide. Done in the prototype of the Pepper Shaker.

All some random thoughts.

Port depth isn't really part of the specs. The thickness of the liner is tied to system size, but the thickness of the wall between firebox and riser is not. As long as you use standard firebricks on edge, thickness between 50 mm and 65 mm would turn out being within reasonable tolerances. I don't have experience with even beefier firebricks but I fully expect those will work as well.

Julian Adam wrote:On the dutch batchrocket site (great that you were able to find the time to update, many thanks!), I saw you mentioned the shorty could also be exhausting in the 'roof' of the afterburner. In that case, where is the port located?

Using a top exhaust, the opening should be at the top front side. It is done and measured towards the end of the development phase.

Julian Adam wrote:Are there running references?

Yes, there are, see this link.

Julian Adam wrote:I'm interested because flow-wise this may be more interesting for my own application.

It's one of the possibilities, use those if it fits your purpose. Please, stay within the current specs, it's a sensitive core that's easily disturbed.

Benjamin Dinkel wrote:This is the core lovingly named Shorty?!

Pros: compact, large window, no secondary air channel necessary
Cons: less initial draw

Correct me if I'm wrong please.

The pros could be extended with: very forgiving at reloading, a choice of core exhaust directions, highly resistant to fuel overload.

So, your very brief description is correct, including the lovingly name.

Rico Loma wrote:If I decide to try this paste in March, could you recommend a specific brand, one you have used ?  I can look at Leroy Merlin, a large network that's only 9 km from the project.  Other small masonry supply stores could have similar pastes. I will look at all possibilities there.

The French call this "coulis silicaté", Google Translate makes "silicate grout" out of that.  It's in powder form, need to be mixed with water. No brand name, sorry. It was OK on the firebricks, and absolutely first class on the red bricks. I had to break a lot of that latter bricks the last day, while demolishing the bench and core.

Rico Loma wrote:1, are those 8 large pieces  i see custom cast refractory slabs? I saw Thomas and Gerry build their shorty core last year,nand I understood how and why  they cast those specific pieces. When I viewed Peter's work via Sketchbook the detail of size makes me think yes. Were those hand cast first , before assembly began?

None of the refractory slabs were cast, those are large firebrick slabs, that's all. Also, this was the material that happened to be available.
If I had the choice, I would use large concrete pavers for the bench, top and seat. The core is another thing, I suspect those refractory slabs aren't available in the US. So, you have to hand cast those.

Rico Loma wrote:2, this was made in record time , much of that praise is naturally to the craftsmen involved.  Respect!  Was refractory cement used in place of 1:3 clay and sand mortar, and what was the reasoning behind that decision (longevity, strength, personal preference? )

The whole of the thing was raised in just three short days, several guys working on the core and the bench simultaneously. The mortar used could have been clay/sand, but we used something else, a very versatile paste, not being refractory as such, very thin seams possible. Again, that happened to be available.

Rico Loma wrote:3, was cob used ONLY for the last gasp, i.e., the final exhaust pipe heading skyward?
Thanks for any answers or opinions.  I understand Peter himself is quite busy always,  in winter months especially. I might give this a try, it would be perfect for a project going in the mountains of Portugal 🇵🇹

No cob was used for the entire thing, just bricks, slabs and the mortar paste. This was specific to France, by the way.
The thing would be a very potent heater as such, able to be refilled almost indefinitely. And yes, winter is a very busy time of year, half of my days are spent in front of my computer screen.

Leonardo Bevilacqua wrote:Then, another set of questions. What about the door?

The doors that I made myself in the past 40-odd years are all of the T-profile type.

Leonardo Bevilacqua wrote:How do I calculate the square pipe section needed, and the cuts that need to be made, and their position?

Use the link at the end my last post, all that you'll need is there. The text is in Dutch, admittedly, have it translated into English or Italian by Google Translate. I do that all the time with text that's in a language I don't understand. Links to the SketchUp drawings are there also, that's a standard 150 mm system. You have to start studying yourself, can't be helped.

Leonardo Bevilacqua wrote:Also, which kind of glass is needed?

Good quality heat-resistant glass. There are two brands in existence, Robax by Schott and Neoceram by Nippon Electric Glass. Both are suitable and pricey.

Leonardo Bevilacqua wrote:Where can I find the formulas to calculate the dimensions of the sidewinder core?

At the moment, there isn't a central place where the figures of a Shorty core are summed up, yet. By the way, the numbers for the sidewinder version aren't any different. I don't know which sketchup file you used for upscaling, so I am unable to check whether it is correct.

But here are the numbers for the calculation, all mentioned numbers are internal.
Start with the base figure, written down as B. This is 72.34% of the diameter of the chimney pipe, equal to system size.
Width of the firebox: 2B.
Height of the firebox: 3B.
Depth of the firebox: 4B, upto 5B.
Height of the port: 2.1B.
Width of the port: 0.5B.
Position of the port in a sidewinder: centered in the port 1B from the rear wall, left or right.
Width and depth of the riser: 2B.
Heigth of the riser: 5B upto 5.5B.
Liner in the bottom half of the riser: left and right equal, seen from the port, double that thickness at the port side.
Height of the liner: 2.4B, also crossing over the port.
Resulting floor of the riser: square, each side equal to system size.
Exhaust opening of the riser: in the same wall as the port, width 2B, total square mm of the opening 100% of the chimney pipe's csa.
Heigth of the opening: follows from the calculation of the sentence above.
Piece of wall above the exhaust opening: same height as the opening.

The above is about a normal sidewinder version, a reversed sidewinder version is slightly different.
The above information should be sufficient to check the upscaled drawing you have there.

Leonardo Bevilacqua wrote:It would be very nice to have a place where anyone can find tables, and perhaps spreadsheets, with all the dimensions for the different types of core.

I am working on it, a Dutch description of the Shorty is online in preliminary form, English will be next. But don't hold your breath, winter is a very busy time for me. See https://batchrocket.eu/ontwerpen#shorty