Satamax Antone

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since Sep 24, 2011
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Southern alps, on the French side of the french /italian border 5000ft high Southern alpine climate.
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Recent posts by Satamax Antone

thomas rubino wrote: mine has been 2.5" for 5 years now.

Thomas, you don't want to try it at 4, for the sake of science?  
18 hours ago
If it's three inches, i shut it!

Thomas, thanks.

This one is even better,

If you immagine what happens in, a T, the two blue regions are increased, even more turbulent, and the gases crashing on a flat surface instead of a sharp point, create even more turbulence. Mixing with the stalling blue adds more and more drag on the gases.
18 hours ago
Yes definitely.

I have explained the calculation. Refer to the link i have posted.

Turbulence in an elbow, boundary layer not wanting to change direction, high speed gases not wanting to change direction, all that means that if CSA and gap surface, (ring projection if you prefer) are equal, your "flow" is chocked. It takes a huge amount of energy to make the gases change direction. Turbulences form on each edge of the heat riser, which are a good inch in diameter, gases crash in the barrel ceiling. All that means there are lots of turbulences.  And the flow of gases can't pass that easily. Plus, gases at atmospheric pressure, are considered as incompressible. So that can't even save the functioning.

See here, in my workshop batch, running in thermal runaway mode.

Do you think this could be chocked within two little inches ? Or am i talking completely gibberish?

This could well illustrate what happens exiting a heat riser. And this is not sharp orifice, but a funnel end.

18 hours ago

Eric Hammond wrote:If I were to do it over, I would make the gap as large as I could and still maintain a 36 inch clearance between the top of the barrel and the combustible ceiling. Seems like that gap should be as large as possible.

Depends what you want to do.

Tighter gaps are for cooking. Larger, to heat homes, and avoid problems!
Well. I will repeat, any gap bellow 1.5x CSA is bound to have problems.

Check this, it could shed light on m'y senseless babble

2 Inches top gap is way too small for an 8

8 x 3.1415926  = 25.13 X 2 (gap) 50.26 square inches.

8 x 8 x 3.1415926 = 201.06 /4 = 50,26 square inches; the two numbers are equal, since there is a direction change, the recommended number is at least 1.5 times that figure.

Do you think a direction change, in such a hot, turbulent and fast stream of gases can occur without losses?  Nope. There's the high speed crashing of the gases on the ceiling of the barrel, then the direction change, twice!

See, this is an 8 or 9 inch gap, into a batch rocket.

My opinion, go for 4 inch gap, since you won't be cooking on a round top. So you don't need the high temp spot in the middle of the barrel.


By the way, do the same calc for your side gap to flue transition, to see if you are within specs.

Graham Chiu wrote:

Satamax Antone wrote:

As this occurs just under 200 deg C, isn't that the right temperature to sear steak ( Maillard reaction )?

BTW, I'm a little confused about the use of steel in your burn chamber.  Aren't we told that we shouldn't do this?
Or is it the expectation that you will need to replace the steel in a few years time?

Yes Graham, but when you have no choice!

I had tried a metal cooktop on the firebox of previous batch prototypes, and that survived. So i thought my square "barrel" would survive, but it didn't. Normally, the whole stove can be dismantled, without touching the bell.
4 days ago
One thing, when i will need to change this riser. I will most certainly make a broken riser

To be able to use the full front window as a oven.
4 days ago