Ernie Wisner wrote:no problem thats why Erica and I hang around here.
have fun experimenting.
and yes you will want the same cross sectional area throughout the stove. (8 inch all the way)
Glenn Herbert wrote:The system diameter does not directly relate to the riser height. It is common to make the feed tube height 1 1/2 to 2 times the system size, so 12" to 16" for an 8" system. Using the 1:2:3 or 1:2:4 ratios, this would give 12:24:36, 12:24:48, 16:32:48, or 16:32:64 feed tube to burn tunnel to riser. (Measured along the outside edges of the components.) The burn tunnel can and should be shorter than 32" in most cases. 1:1.5:3 is another ratio I have seen, which would give 16:24:48, quite practical with standard materials. I would not cut the barrel down in any case; the taller the riser is, the better, within reason. Extend the riser to make it 2" below the barrel top.
An 8" J-tube system can ordinarily support up to 50' of horizontal ducting, minus 5' for each 90 degree elbow.
Thomas Tipton wrote:Has anyone ever built a rocket stove with multiple risers? And if so, what were the results?
If it failed, can you describe the failure mode.
Thank you for taking the time to read through my crazy.
Thomas Tipton wrote:... so while I have your attention perhaps you might indulge me on why you attempted the twin riser design. Were you attempting to lower the riser height requirements as I am doing, or was it for another reason? Just curiosity perhaps?
Thomas Tipton wrote:Thank you again. It's a great honor to hear from you.
I would suggest that you may want to make the tall bell only as large as it needs to be for proper function, and add a bench-style bell to absorb the rest of the heat before sending the exhaust to the chimney.
Long runs of parallel ductwork would have less of this issue, as friction would increase dramatically with increased flow, tending to equalize the competing paths.
Erica Wisner wrote: I have never seen one that was an improvement on the brick J-tube, for smokeless performance. [Edit: As of 2018, I have now seen 2 batch box models built and operated by Peter van den Burg, that did burn amazingly clean. However, I've also seen other people have major smoke issues using the identical batch box stoves without Peter's meticulous procedural care.]
Jeremy Cash wrote:Before I designed my Rocket Stove I consulted with my engineer brother-in-law who guided me in the right direction to understanding exactly what makes a Rocket Stove "rockety". Because I am ADHD I hate wordy posts so I will try to keep it simple. My hope is to help everyone understand what is happening inside the Rocket Stove so they can improve their own designs. I am in no way a math wiz and so I plugged these formulas into an excel spreadsheet and played with the numbers so I could make the most of the stove.
The primary factor driving the force within the rocket stove is the "stack effect". The larger the heat riser, the faster the flow will be. The other is the difference in temperature of the fire box and the outside air.
In my stove I used fire brick, a 10" heat riser 1.5" thick and a 55 gallon drum.
I used Paul's portable rocket mass heater design and made some minor tweaks.
I discovered with trial and error and calculations that the size of the intake is not as important as the size of the heat riser. If you take a look at the "ventury effect" you can see that a smaller opening will actually help increase the air speed over the burning sticks also improving the "rocketiness".
I chose a 10" heat riser by using a basic formula based on the 23" diameter of the drum. In the flow equation A = the Area of a cross section of the heat riser. To prevent a bottle neck past the heat riser if I use a 10" heat riser + 1.5" of insulation totaling 3", the remainder is 10".
I said I will keep it short, I hope this helps get some wheels turning. Feel free to comment. Thanks. I will try to post pictures later. Thanks to those who introduced me to an efficient way to heat things up.
Erica Wisner wrote:
I have fond hopes that someone with good welding skills will help develop even better rims, or even decide to manufacture them, for supporting generic barrels. But this works pretty well for now.