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John Appleyard
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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?
 
allen lumley
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John Appleyard : Congratulations for thinking outside the box ! You need to find a non-flamible kind of piping that will survive the 1300ºƒ + Temperatures

that a rocket mass heater RMH, burns at . Further, Due to Oxidation and ''High Temperature Hydrogen Attack'', also called ''Hydrogen Embrittlement'' ALL

metal is doomed within the combustion zone !

Just like a Tall Final Vertical Chimney draws better than a Short Chimney We need The Heat Riser to be 3 - 4 times the length of the Feed tube to provide the

strong draft we need without blowers. It is the increased length of the Heat Riser that provides the Exposure of Time, Temperature, and Turbulence needed

for the Freaky high combustion temperatures we need to get the efficiencies and clean burn We are looking for !


With no barrel and no thermal mass you will only be able to use avery small % of the Heat Energy your combustion creates, The Rest will just go up the

chimney!


The Nearest thing that exists and is close to what you are trying to create is the Pocket Rocket, You can certainly experiment with this outdoors or in another

safe place. This can be scaled down to the size of a Metal 5 gallon pail, or a lidded garbage can. Because of the amount of air drawn through the Pocket

Rocket to make provide a clean burn and also the lack of any thermal mass- as soon as the fire goes out you will be instantly cold again !

Hopefully this is both timely and Useful For the good of the Craft ! Big AL



 
John Appleyard
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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!
 
John Appleyard
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"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".
 
allen lumley
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John Appleyard ! I stand corrected ! High temperature Hydrogen attack is one of the causes of Hydrogen Embrittlement ! Hydrogen Embrittlement is the effect

on most steels when single atoms of Hydrogen enter the steels pore spaces and recombines with another single atom of Hydrogen or Carbon !

One is a cause the other is an effect !


I do not know which 6'' pipe you are referring too, often with a six inch system the pipe lining the inside of the Heat Riser is there to be a sacrificial form for the

heat riser which is made from Perlite and Clay slip, with or without using ''Water Glass''as a hardening agent !

Truck or Lorry I can not recommend any damper in the smoke pipe until you have proven your Wood Heater to be Air tight ! Good luck, Big AL


 
John Appleyard
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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.
 
allen lumley
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The problem would be reproducibility ! I expect that a propane burner like used for Deep frying whole turkeys can be used to create a steady state test bed,

It costs tens of thousands of dollars to get a new appliance a Underwriters lab test rating and unless we are talking pellet stoves there is not much of a way

to maintain the change from solid fuel to gasification and combustion from moment to moment ! Big AL
 
John Appleyard
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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.
 
allen lumley
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- !5% at say 1200ºƒ seems pointless, however I and many of your other Fellow Members are looking forward to your posts on the subject ! Big AL
 
John Appleyard
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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.
 
Glenn Herbert
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There is a severe surface friction effect at a certain range of reduction in pipe diameter. It has generally been found that 4" diameter is the smallest RMH that can be made to work well, by experience or luck. A rocket stove which has no downflow component or mass ducting friction to deal with can be smaller, I don't know how much smaller. I believe 3" systems have been successful, though I can't point to a specific source.

Part of what makes for complete combustion is an insulated burn chamber, which means these pipes need to be extremely well insulated or they will tend to cool the combustion too soon. It would probably be easier to have a single riser above your firebox with refractory masonry walls, possibly with irregularities which create turbulence to slow the flow without cutting it too much.

Your plans for a glowing coal bed overnight are precisely the polluting effect found from ordinary woodstoves used in the ordinary way.
 
John Appleyard
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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
 
Glenn Herbert
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Okay, if you mean just red hot and no longer combusting, that would obviously be non-polluting... although the amount of heat stored in that would be minuscule. Much more heat would be stored in the metal enclosure, for as long as it lasts.

A small system that would heat a 7' x 14' space without overpowering it would probably be 4" equivalent or less, which would not need much height in a single riser (possibly around 2') to get as complete as combustion will get. You could even make the riser of a heavy steel pipe say 4' tall, and insulate to varying heights until you find the best balance of combustion and radiation.
 
Did you see how Paul cut 87% off of his electric heat bill with 82 watts of micro heaters?
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