Thanks for the screen shot, the mac spreadsheet thing didn't work, so the table is very handy.
Where it says "calculated base" what does this refer to? It seems obviously related to the height whatever it is.
Also the ratio between CSA and height decreases as you go up in system size according to a constant pattern. So the ratio between height and CSA of the 4" system is pretty much double that of the ratio between height and CSA of the 8" system, and three times the ratio of the 12" system.
What the formula underlying this - sorry maths was never my strong point - there is some pattern to it is there not?
The original calculation was done by Jim (jham) from Southern Virginia. This is the thread where he explained his calculations.
He elaborated about it by PM, but I'd think it's alright to publish this here:
Oct 12, 2012 at 6:11pm Hi Peterberg, I wanted to get back to you sooner about the way I attempted to derive the measurements of my stove from your sketchup example but I have been busy at work and home. So....here I go.
I took your measurements and saw that by using bricks in the sketchup model you had made every linear measurement a ratio of a basic unit. Because the clearest ratio you talked about was the 3 to 2 ratio of the firebox opening, I took the firebox opening and divided the height by 3 to use as the basic unit. So 1 unit = 108mm. I then just converted all the linear measurements of your model into multiples of the basic unit. The only measurements that were not a simple multiple of the basic unit was the width and height of the burn tunnel. I just rounded those values (burn tunnel W and H) to simple multiples of the basic unit (108mm) and came up with W=54 (.5 units), H=216mm (2 units). To figure out all the values for my stove I started with the diameter of the heat riser pipe (100mm) I wanted to use, and got the c.s.a of the heat riser 7850mm2. I then multiplied that times 4 for the c.s.a of the firebox and got 31400mm2. To get my basic unit of linear measure for my stove I then took the formula for the c.s.a of the firebox opening and plugged in the numbers I knew: 3 x unknown single unit x 2 x unknown single unit=31400 (the c.s.a of firebox). I then solved the equation to derive the single unit: 6 x unknown unit squared=31400
unknown unit squared=31400/6
unknown unit squared=5233
unknown unit=square root of 5233 or 72mm
I took that basic unit and plugged it in to unit measurements I had figured out from your model. As an example, the heat riser height on your model was 11 units high (108 mm x 11=1188mm) so mine was (72mm x 11=792mm). I apologize if I am not doing a very good job of explaining myself, math is definitely not my native language
I think that this method of scaling worked well because the stove works well. I have sealed and insulated the heat riser more carefully since the last time I posted and the stove is working better than ever. I am going to start a thread today asking for some design help with a planned application. Thank you again for all your data you have shared.
Later on, I've done some recalculations myself and arrived at this conclusion: It is entirely possible to culculate the base dimension by taking 72.36% of the diameter of the riser. So, define the riser diameter, preferably the same as the exhaust pipe, and do this simple math.
Actually, in the model Jim calculated the port is slightly larger than 72% of system size. Minus the overhang of the p-channel it will come down to the 70% target.
The reason why the port is narrower than system size: it promotes a higher air velocity in the port itself and slows down immediately behind it. This do promote a very effective turbulence without adding more air into the fire. Supplying more air as a method to induce turbulence is being used by everyone who like to promote better combustion, with the obvious disadvantage of cooling the fire and enlarging the amount of excess air.
I've tried smaller and wider ports as well, results were not as good. So yes, the constant could be 72.36% but the question of why isn't answered.
Tantalizing, don't you think?
Last Edit: Aug 27, 2013 11:26:27 GMT -8 by peterberg
vimes1984: I've heard about a calculator, does anybody have a link?
Oct 21, 2016 11:00:12 GMT -8
scott55y: Are there instructions for building a casting mold for an 8 inch batch box posted somewhere?
Oct 25, 2016 10:00:18 GMT -8
yellowdog: Yellow , just trying to learn how to post here
Nov 30, 2016 3:44:24 GMT -8
robert1171: In a batch rocket heater does the riser still need to be 2 inches to the bells top?
Dec 20, 2016 9:19:52 GMT -8
robert1171: I am building a batch rocket mass stove. is it ok to make the heat riser out of pro firebrick and in a square design as to a compared circular castable riser ?
Jan 15, 2017 12:29:15 GMT -8
keithturtle: This guy did successfully https://www.youtube.com/watch?v=ZKOm3Qqxns4
Jan 15, 2017 19:29:26 GMT -8
pluton5: witam wszystkich,,,od czasu mojego pierwszego wpisu minęło juz kilka lat i tradycyjne palenisko RS ( rocket stove) zmieniało sie już wiele razy.Zmieniony wygląd i sposób zasilania palnika. Od pewnego czasu zmianił sie też kształt samej komory załadowczej
Jan 24, 2017 10:40:44 GMT -8
tommy: I have a j style rocket stove I am having a hard time getting it to draught right and make the right noise
Jan 24, 2017 15:37:52 GMT -8
esatto: looking for experience with mortar/clay slip experience... 2 bell 7' system ...old solid red clay brick bottom 2/3 of first bell and hard fire brick on top 1/3 of primary bell(above riser) looking for anyones experience with what works?
Jan 26, 2017 19:04:29 GMT -8
jura: @ Pluton5 I do speak polish, but I think the rule of the thumb on this forum is using English.
Jan 27, 2017 4:36:22 GMT -8
jura: @ Pluton5 I believe we are in deep need to use unified RS builder parlance in PL Lng therefore I'd propose to use "dopalacz"(heat riser) and "palenisko"(batchbox) (instead of "palnik" and "komora załadowcza")
Jan 27, 2017 4:41:28 GMT -8
barbalha: I want to build rocket stoves in Spain, where I live. I'll be in Phila. Till Feb. 21. I'm hoping someone here needs my volunteer help so I can learn more
Jan 28, 2017 15:18:03 GMT -8
mickykrovo: I have decided, (after few weeks) to become a "full member" of this great society. I have found it very helpfull so far.
Jan 30, 2017 10:39:37 GMT -8
panos: In order to put the p channel ,you have to make a hole ot the top plate of the firebox ,right?
Feb 6, 2017 7:46:40 GMT -8
cfrith: Panos; Yes directly inline with port with appropriate depth into port and correct width according to peters batchbox dimension chart
Feb 12, 2017 14:38:51 GMT -8
panos: Thank you very much! Have a nice day.
Feb 14, 2017 15:47:23 GMT -8
panos: Can i costruct the bell with this type of brick ? https://www.google.gr/search?q=brick&biw=1242&bih=602&source=lnms&tbm=isch&sa=X&ved=0ahUKEwiEl6uF96nSAhWIFJoKHTiRAI8Q_AUIBigB#tbm=isch&q=%CF%84%CE%BF%CF%8D%CE%B2%CE%BB%CE%BF&*
Feb 24, 2017 15:55:01 GMT -8
panos: i guess these would be good for making columns inside the bell since they have this additional surface area.
Feb 24, 2017 17:59:35 GMT -8