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Smaller batch box and design tweaks

 
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Hi, new here.

Ive been researching PVB batch boxes for a while and have a few questions about a design I wish to implement

Using the ratios on batchrocket.eu I have calculated the size that a box with a 2" riser would be. I havent heard of a box that small being attempted before, and Im curious if the drastic change in size will adversely affect efficiency.

second, I also wish to implement a few design tweaks to the original batch box and once again would like to ask if about potential losses or gains.

the first and foremost tweak would be moving the port to the top of the firebox, rather than the rear, similar to the double shoebox design seen on peter van den berg's more recent videos. However, unlike the more square shape seen in his videos, I would like to retain the long(tall) narrow port that the original batch box design has.

I have questions about the double shoebox design in general, how efficient is it compared to a regular batch box. How do the measurements in a horizontal riser compare to that of a vertical one, considering that in the original design the riser is taller than the firebox is long. could the horizontal riser simply be shorter and retain the same CSA as a vertical one, or would the CSA have to increase to account for the shorter length?

can a vertical riser be used with a port that rests on the top of the firebox?

another design change I wish to implement would be moving the 45° angles from the bottom corners to the top corners of the box.  I am unsure about whether those would extend all the way back in the firebox or stop just shy of where the port would begin.

Finally, If the port is on the top, could the p channel simply be straight into the port rather than L shaped down into the firebox

If any or all of my questions could be answered, that would be great. I have included a few rudimentary drawings I have to illustrate certain design tweaks
IMG_20200914_194731097.jpg
RMH measurements
RMH measurements
IMG_20200914_194657141.jpg
front and side concepts
front and side concepts
IMG_20200914_194715990.jpg
too concepts
too concepts
 
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Big Welcome to Permies Mr. T
Hope your stay here is educational and uplifting to build the stove of your dreams...

There is a reason Peter has not gone below the 3" he has listed on his chart. Even that small may not work very well due to the inherent nature of fluid dynamics (which are very similar to gas flow behaviour as well) and this influence is called the boundary layer. There is a certain distance away from the sidewalls where there is turbulence and friction that affects the gas that flows through the system making it difficult to get a system that will flow properly. For a great description, see Stove Chat Episode 11 around the 53 min mark.

second, I also wish to implement a few design tweaks to the original batch box and once again would like to ask if about potential losses or gains.


Peter has done almost every kind of modification there is to have settled on the numbers he has published. You are certainly welcome to experiment yourself but to improve on his batch box design is probably not going to get you a more efficient stove. Matt Walker has done a lot of experimenting on Peters design and you may want to check out his variation called the .
Walker riserless core


 
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T Giles wrote:Using the ratios on batchrocket.eu I have calculated the size that a box with a 2" riser would be. I havent heard of a box that small being attempted before, and Im curious if the drastic change in size will adversely affect efficiency.


Hi T, I understand you are aiming for a 4" version of the DSR1. First, a 4" batchrocket of any version is not a practical thing to use although it can be very powerful. The problem lies in the fact you have to feed it quite often with small sticks in order to keep it going. Second, the DSR1 didn't cut the cake in a real life situation inside two barrels and coupled to a decent chimney. In fact it went in thermal overdrive 50% of the times I fired it, consuming fuel faster and faster at an alarming rate until it was too much for the afterburner function to cope with. Resulting in lots of unsightly black smoke until all the fuel was gone.
No gains to harvest, rather the opposite.

T Giles wrote:the first and foremost tweak would be moving the port to the top of the firebox, rather than the rear, similar to the double shoebox design seen on peter van den berg's more recent videos. However, unlike the more square shape seen in his videos, I would like to retain the long(tall) narrow port that the original batch box design has.


Please have a look at even more recent videos, starting with Batch Box Rocket Stove 20 up to and including 24. That's about another implementation of the Double Shoebox, Mark2 in this case. This one has led to a complete and thoroughly tested version which works surprisingly well. Mind you, development of this one took a full year.

T Giles wrote:can a vertical riser be used with a port that rests on the top of the firebox?


No. Tried that one a long time ago, been there, done that.

T Giles wrote:another design change I wish to implement would be moving the 45° angles from the bottom corners to the top corners of the box.  I am unsure about whether those would extend all the way back in the firebox or stop just shy of where the port would begin.


Those 45º angles are there to concentrate the charcoal in the middle of the firebox, they won't have a function on the ceiling at all.

In case you are looking for a simpler and more compact batchrocket design, have a look at https://donkey32.proboards.com/thread/3503/double-shoebox-rocket-mark-ii It's quite a long thread but worth to read it all, if you are interested of course. Some remarkable features are incorporated in this particular design, I got it to the point where it was unable to go into thermal overdrive. No matter what I did to it, it simply refused to belch smoke.
This design isn't published on batchrocket.eu yet, mainly due to health issues. But drawings in SketchUp format are available.
 
T Giles
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thank you for responding. I took the time to read through those donkey boards and theres just a little bit of information I still need.

how tall is the top box compared to the firebox, should the riser stub be flush with the top box back wall or should there be space,

and how large should the stumbler block be
 
Peter van den Berg
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T Giles wrote:how tall is the top box compared to the firebox,


The front of the top box is square, i.e. width and height are equal to the width of the firebox.

T Giles wrote:should the riser stub be flush with the top box back wall or should there be space,


The best results were obtained with a firebrick liner of 30 mm on three sides of the riser stub, left, right and rear. A couple of months ago I tried the development model (a 125 mm or 5" version) without this liner. Don't leave it out, results were dramatically worse.

T Giles wrote:and how large should the stumbler block be


For the 150 m (6") version that would be approx. 40x40 mm (1.57" x 1.57").

Here's a complete drawing of a 150 mm (6") version.
https://pberg0.home.xs4all.nl/pictures/dev2018/DSR2/DSR2%20closedv8.skp

And three different setups as an open version.
https://pberg0.home.xs4all.nl/pictures/dev2018/DSR2/DSR2%20openbrickv8.skp
https://pberg0.home.xs4all.nl/pictures/dev2018/DSR2/DSR2%20opensplitv8.skp
https://pberg0.home.xs4all.nl/pictures/dev2018/DSR2/DSR2%20openv8.skp

The DSR2 is a very tight design, even more so as compared to the basic batchrocket.
 
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I love the work that Peter has done, and the files he has put up in Sketch up, which I certainly can download (and have done)

Is there anyone on here that can convert these to a file format that I can bring into my SolidWorks.  Simply being I have used solid works for over 20 years now, and know it inside and out, and for some reason seem to founder around the Sketch up workings.

Google says I should be able to export it as a STL file, which I presume would work fine, (this is exporting from Sketch up) but all I get is " if you wish to export, upgrade to Sketchup Pro)  Which I don't want to do.

If someone here knows the trick? or can do, I would appreciate it.

thanks in advance.
 
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