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
mercedes: Not sure where this question will end up...I just registered. HOW THICK SHOULD PERLITE/VERMICULATE/CLAY INSULATION BE BEHIND THE THERMAL BATTERY/COB BENCH IF IT BACKS UP TO A STRAW BALE WALL? Thanks! Can you please also post me: email@example.com thnx!!
May 28, 2018 20:05:23 GMT -8
kkp: Mercedes: Benches don't get real hot. In fact, they are rather cool compared to other areas. You shouldn't need a mix like you described
Jun 7, 2018 18:10:52 GMT -8
maartenmartens: beste Peter, ik heb je eergisteren een mail gestuurd via het contact formulier op je website , heb je die goed ontvangen ? mvg Maarten Martens, architect - geobioloog (mail betreffende de bouw van onze eigen RMH)
Jun 20, 2018 13:21:57 GMT -8
martinm: any one here with info \ experience with heat (from a mass heater) distribution with ducts throughout two storey house ?
Sept 8, 2018 22:58:52 GMT -8
padica: Good morning, this is a wonderful subject, please someone can help me with the theme of double and triple combustion, how it is achieved, theory and design, thank you
Sept 15, 2018 7:13:40 GMT -8
wiscojames: I'm afraid you won't get a response to such a vague question - I suggest reading through some of the threads related to your questions before asking for an explanation. People will be very generous with their knowledge if your question is more specific.
Sept 18, 2018 4:48:00 GMT -8
daniel: in my experience as I am working now on something of that nature, I have thought of making a heat exchanger and distributing the heat through vents using a slower fan. Now after a few years I realize that mass heaters give out primarily radiant heat, for
Nov 30, 2018 12:48:38 GMT -8
coastalrocketeer: Anyone posting in this shout box... if you have something you want people to see and respond to, create a thread in the appropriate forum section... this is not the place...
Dec 16, 2018 18:10:49 GMT -8
vesuvius: High Temperature Glass options,
Jan 4, 2019 16:28:17 GMT -8
vesuvius: Do any of you have experience with using the glass from home oven doors on a rocket stove? I'd like to have a viewing port on my stove but don't want to fork out for new ceramic glass. Any thought as to whether it would take the heat of a rocket stove?
Jan 4, 2019 16:30:40 GMT -8
yaya: you dont need the blowair for that temp..
Jan 13, 2019 16:43:57 GMT -8
flybywire: Glass window from an old washing machine is designed to take high temps. Cheap solution to your need.
Jan 27, 2019 0:10:58 GMT -8
coastalrocketeer: Anyone posting in this shout box... if you have something you want people to see and respond to, create a thread in the appropriate forum section... this is not the place to have a discussion... it is for short announcements
Feb 7, 2019 0:11:23 GMT -8
coastalrocketeer: you won’t likely get replies to questions here, and it is not a spot that makes holding an ongoing discussion possible...
Feb 7, 2019 0:12:22 GMT -8
TexasGonzo: Sooooo glad I found this site! Its always rewarding to find such a super group of folks! To any and all, feel free to PM me anytime. Thanks for having me!
Mar 11, 2019 18:56:41 GMT -8
jlmtech: GADGET: CONSIDER USING A JET PUMP INSTEAD OF A BLOWER FAN TO INDUCE DRAFT; NO CLOGGING.
Mar 26, 2019 8:19:28 GMT -8
michaelegan: i am unable to open the sketchup files on my mac. I used sketchup a few years back but apparently the company now requires a subscription. does anyone have any advice/instructions on how to use the program or how to view pictures without spending money?
Aug 20, 2019 18:41:48 GMT -8
mannytheseacow: michaelegan: download AutoCAD student version for free... import .SKP
Aug 23, 2019 13:33:44 GMT -8