John Appleyard

I've seen a small stove with a 2" flue.

No space or weight capacity for single masonry risers.

Glenn Herbert wrote:
Your plans for a glowing coal bed overnight are precisely the polluting effect found from ordinary woodstoves used in the ordinary way.

Hardly, it is unburnt gases which is the pollution problem. Once you're down to the char and not providing it any air its effectively thermal mass. Perhaps my choice of the word "glowing" was a bit keen, but i'm looking at a 3/4 insulated firebox

15% on the length of the riser pipe, that is where all the gas is burnt, some of which will soak up changes in fuel and conditions.

John.

Such accuracy is pretty pointless in this case, want I'm after is getting a few points on a graph so I get a curve out of it. For me a 15% tolerence would be enough to know I wouldn't be wasting performance or getting incomplete burn. I expect that'll be 1/2" of riser. John.

Ah, as a former it makes sense then.

Hydrogen embrittlement sounds like a different thing entirely though, http://www.twi-global.com/technical-knowledge/faqs/material-faqs/what-is-high-temperature-hydrogen-attack-htha-hot-hydrogen-attack/. But anyway.

Has anyone done any experiments to find the relationship between pipe diameter and combustion? First stage of my build is set to do this experiment with observable pipes of different diameters but I was wondering if there's anybody else who's on it?

I guess that's a no so far.

John.

"The main factors influencing HTHA are the hydrogen partial pressure, the temperature of the steel and the duration of the exposure. Damage usually occurs after an incubation period, which can vary from a few hours to many years depending on the severity of the environment. High temperatures and low hydrogen partial pressures favour surface decarburisation while the opposite conditions favour fissuring. In addition, the composition of the steel influences the resistance to HTHA; in particular elements that tie-up carbon stable precipitates such as Cr, Mo and V are very important. Increasing content of such elements increases the resistance to HTHA, so that chromium steels with more than 5% Cr, and austenitic stainless steels, are not susceptible to HTHA."

Also, Hydrogen Embrittlement is "not to be confused with HTHA".

Due to Oxidation and ''High Temperature Hydrogen Attack'', also called ''Hydrogen Embrittlement'' ALL

metal is doomed within the combustion zone !

So why is 6" pipe stated as an alternative in the 6" design? I will look into though, thanks.

Friction pressure loss http://www.engineeringtoolbox.com/duct-friction-pressure-loss-d_444.html also has a part to play in time in the pipes? very minor in larger pipes so it won't have been a factor in the standard designs. I found this after posting. As per my theory I think.

It will have a ~7' vertical flue creating draw. Draw gain No. 2 in the short riser model is the flue doesn't need a section going down, a major function of the barrel, getting the hot air down, to be used in the mass. No.3 It doesn't have a feed tube to service, the riser pipes sitting directly above a firebox.

I can't really compare a RMH to a stove for a truck, just nick the idea of the riser pipe in a closed stove. Yes I'm gna lose heat up the chimney, but hopefully a lot less energy as all the gases will be burned off, it should also be a lot cleaner for the environment. There is also the firebox which can be closed down overnight, so I get a box of hot embers for prolonged heat. I also need to say that in the UK a "truck" is generally a vehicle with max gross weight of 7.5T or more, I have a 14' x 7' insulated living space so I don't get instantly cold again, the difficulty is control so I don't get too hot!

I live in a truck so due to space and weight thermal mass is out of the question. I have a stove design lined up which has multiple riser pipes of a smaller diameter in parallel. I'm assuming that the width of the pipe affects the speed of flow through the pipe due to resistance. Therefore smaller diameter pipes can be shorter and still allow complete combustion because they allow the required time for combustion. I then put multiple pipes in parallel to acheive the required draught. Yes, this would mean you wouldn't need a barrel in your house...

Has anyone done any experiments to find the relationship between pipe diameter and combustion? First stage of my build is set to do this experiment with observable pipes of different diameters but I was wondering if there's anybody else who's on it?

I've tried something similar, a gas bottle with a flue pipe up the middle. I was thinking of using it as a stove for outdoor cooking. I had it catching heat from below as well but reckon it would need to be well insulated which was detracting too much from my intended use so project suspended.