Batchrocket.eu, information site

[peterberg]

Thanks Terry, as always!
I tried to circumvent the triple 'heat absorbtion area', have a look at it when you are up to.
I'll do the announcement on permies and here. Have you pondered about replacing the whole of bell theory and sizing story out of Applications?

[terry]

Jun 12, 2016 0:45:03 GMT -8 peterberg said:

Thanks Terry, as always!
I tried to circumvent the triple 'heat absorbtion area', have a look at it when you are up to.
I'll do the announcement on permies and here. Have you pondered about replacing the whole of bell theory and sizing story out of Applications?

looks good peter, and am very glad to see you used what I wrote only as a starting point, with enough changes that it even started sounding like you and not me! It reads well, not too fussed about any residual 'heat absorption area' haha.

re the re-ordering.............TBH I have not put too much thought into it. I think the only real problem is that one page has become larger than others, kinda imbalanced. Is that really a problem tho?? After all, the introduction page is quite short, and you would not expect anything else.

So I'm gonna bail on this one, and leave it up to you, it is after all your hard earned website. If you do move it, then (very possibly?) changes would have to be made, so just as long as you know I am happy to work with you on that then it comes down to what you think best.

BTW, my daughter turned up without notice this weekend, so we did a little bit of videoing. I had not expected her to be here for at least another fortnight. Beautiful blue skies today, not a single cloud in sight.

Man, it's going to be a boring video! There was just the slightest bit of smoke visible to the eye at certain angles that will not show up on video. Which is kinda the whole point of these heaters, but I was hoping at least for SOME smoke to appear so that it could disappear. Anyways, will see what happens, maybe (like my ugly installation) we can 'pretty it up' enough to be useful.

EDIT just noticed something (probably tons of them but what the heck)

'When we put these two elements together, the combustion units described earlier coupled with a bell, we have made ourselves a bell heater. As you will see from some of the sketchup drawings we combine these two elements so that the very hot, very clean exhaust from the combustion unit enters the bell and 'allow the magic to happen. The combustion unit can be external or internal to the bell.'

Missing the closing quotation mark. probably needs an 's' on allow??

[tadiv]

I read an article on the website 'BELL SIZING', I found this: "The gap between the top of the riser and the top of the bell should measure at least 30 cm (1')."

Which is the correct size? I think the 30 cm, means 10".

Thank,

Tadiv

[peterberg]

To be precise: one inch (") is 2.54 cm, one foot (') is 12 inches which equals 30.48 cm. The 30 cm is rounded off, that's all.

[tadiv]

Oh, I'm so sorry, you're right, this sign is really (') foot sign. Thanks

[martinm]

I posted a drawing of a double bell heater I intend to build this coming summer and on the first bell I am planning to set a plate of solid piece of volcanic tuff stone. I amsure it will withstand the extreme heat over the riser , the only concern I fave is the expansion of the stone piece and the connection between the double skin on which the plate is set. Perhaps there should be no difference in the expansion of the wall elements (bricks) and the stone plate, since they are similar. My plan is to order 8cm thick plate for the top of the first bell.

Our heater is heavily insulated on top so it will get quite hot there. Let's put it this way: when running at full tilt the riser is spewing hot gases at temperatures as high as 900 C (1650 F). Most of the time the top gap between riser and bell ceiling is about 30 cm (1'). Normal concrete starts to break down long before that level of temp is reached, so it won't be safe to use unprotected sidewalk pavers to name just an example. Reinforced concrete isn't safe as well, the steel bars will expand more than the concrete so it will be torn apart.

The 30 cm distance rule - this is to give more "freedom" of the hot gases ? I do have experience with basic rocket stove but never built a masonry heater.

[peterberg]

The whole thing about the batch rocket is gas velocity. In order to mitigate friction in the gas path I recommend a large top gap. There's no practical maximum by the way, once I tried a gap of 150 cm (5') on top of a J-tube and the thing kept running admirably. Batch boxes are no different in this respect.

[tadiv]

It means the 30 cm (1') is a recommended minimum distance between bell ceilling and the riser? This distance can be increased? With recommended ISA it result a thinner bell, isn't it?

[peterberg]

I think you mean narrow, in that case the answer is yes.

[gugaiz]

Hi, I am not sure if there is a mistake on the drawings or I am not making the calculations right... under the "Brick sidewinder core" section it says that the calculations have been done over a 160mm system. When I opened the sketchup file I saw that the firebox width is 216mm instead of 231mm as it should be for a 160mm. Anyway the thing that caught my attention was the floor vertical channel's dimensions.

As for my calculations the vertical section of the channel should be 1085mm2 (5.4% of riser section) and on the drawing is 961mm2 (31mm*31mm). The horizontal area should be 1658mm2(8.25%) and on the drawing is 1456mm2 (26mm*56mm). The measurements on the drawing match the areas for a 150mm system, so I was wondering if that is aceptable or it is a mistake.

I was also wondering if the firebox's depth, on a sidewinder system can also be upscaled a bit to allow bigger firewood, I am asking that because of the sentence "It would be sensible to keep the same depth as in the straight brick core version."

[peterberg]

I checked it and you are right. I also had to check the notes I made at the time and there's a reason why the figures don't match. I used whole bricks for the firebox and the standard duct which was still closest to the ideal. Matching sizes for the metalwork simply aren't available, I try to avoid custom made sizes if I can.

The alternative was to cut nearly all the bricks to match the figures for a 150 mm system. This is an example of how people need to meddle a bit with the numbers when their materials are different from those over here (which is almost always the case as far as bricks are concerned). The jump from 150 to 160 mm is one of approximately 6%, I'd regard that as acceptable.

About the depth of the firebox: I presume it could be somewhat larger but that configuration isn't tested. To be on the safe side, I wouldn't stretch it more than 30%. Alternative is to scale up the whole of the core if you insist on longer fuel. Having the firebox very deep isn't handy by the way, you need to reach inside everytime the thing is fired up.

[Jura]

Dear Peter


I have a simple question as to necessity of using of a vertically placed piece of metal at the entrance of the floor channel. The one placed between slants @ the entrance of a firebox.
  Here is the photo I mean.
I'm trying to figure out  whether the  aim of such solution is to block air flow or any other I cant come up with.

Does it not  stand for a hindrance  while grabbing the dust off the box?

[peterberg]

That piece of metal is called the threshold. It's sole purpose is to restrict the airflow in the firebox.
In fact, all the air is coming in low through the door, exactly at the same level as the floor channel but at a distance of an inch or so. Imagine that the incoming air is icy cold as compared to the interior of the firebox, so this cold air has the tendency to form a puddle in front of the floor channel and the steel threshold. So whatever small the door opening is, the floor channel is always served first. The rest of the incoming air is going up and over the threshold.

The primary air and secondary air can't be defined by an opening since the air velocity is radically different in the floor channel as opposed to the main firebox. On top of that, the respective velocities are changing during the burn so the inlet arrangement should be tailored to that phenomenon. My own heater, the red bell, is operated like that. The whole of the air inlet is 22% of the riser csa, at the start the door is open a crack too. When the chimney temperature is rising to 60º C (140º F) I close the door. Rising to 90º C (195º F) I restrict the air inlet to 10% of riser csa, flames in the firebox will get quite lazy but the afterburner flame keep on raging like nothing else. The air velocity in the floor channel is very high, in the firebox just a trickle. As such, the air supply could be implemented as an automated system, steered by the temperature of the chimney as the main parameter.

As you can see, this isn't just a matter of how wide the respective openings are. Based on how much air is supplied by which source and at what air speed. In fact, it's all about volume of air streaming in, where and at which stage of the burn. Level of sophistication is just a step up from the simpler p-channel arrangement. The floor channel is very easy to replace as an added bonus, the very reason why I decided to give it a go.

I use a scoop which I operate sideways when taking out ashes, so the threshold won't be a restriction. When I don't take out ashes for a week or more, most of the carbon in there is combusted as well so the volume is greatly reduced. The mineral portion of the ashes tend to be sintered by the heat, it feels like sand. Leaving it longer it will form lumps or "clinkers".

[Jura]

I believe if you were a teacher you would also be as great as a stove constructor :-).
The way you explain issues is perfect.
"How's" and "why's" directed and links between them explained too.
Hat tip and respectful bow. 

If the topic I touch beneath is too off topic here - just a word from you & I'll move it to another thread.

In case of our stove the air inlet is situated under the firebox (the box is elevated by 40 cm) and will serve both primary and secondary inlets. 
The air duct goes ~ 6 m under a floor of the house and starts and ends with a flap.
I wonder whether the incoming air has enough time to warm up by touching the floor of the firebox or I'd rather stick to a rule of perfect insulation of the firebox and insulate the floor giving up the idea of air heating up this way.

Are you familiar with any thread where pros and cons of external vs internal air supply are disputed?

[peterberg]

Before you install this outside air supply, please read woodheat.org/the-outdoor-air-myth-exposed.html, there's a lot more very reliable information on this site.

Personally, I'd avoid external air supply in the heater itself as the plague, more often than not it is riddled with problems. You think your heater will be airtight but it almost certainly isn't. The same goes for your house, on a much larger scale. When the heater is running using air from the room itself, it will suck in air from outside, thereby refreshing the room air which is a good thing in itself.

One of my acquaintances likes to put it like this: why would you feed fresh air to the heater and breath the farths and stale air yourself?