William Bronson wrote: I have done as much to aluminum cans in a campfire.
A dirty,smoke campfire.
The point of high tempature is efficiency and cleanliness of the burn.
Is there any evidence that the actual flame path is any hotter in an insulated core than in one which is not (all other things being equal)?
Is there really any reason to doubt that such a J tube is really an RMH?
Kyle Neath wrote:
The laws of thermodynamics will say that the insulated version is always hotter than a non-insulated version since the insulation contains heat inside, while the non-insulated version radiates heat away. Now, how significant the difference is — that's a good question. I'm definitely not versed enough with the style of testing everyone's been doing to give you guidance there.
Hi Kyle. I certainly understand the "theory" but I just wonder how or if it works out in actual performance in the actual temperature of the flame path where combustion of the wood gases actually takes place. I know for a fact that when you insulate the core, it just continually heats up simply because the heat has nowhere else to go and a steel core and heat riser will eventually glow red hot from bottom to top and of course corrode away very quickly. But does insulation or no insulation actually affect how hot the combustion is. i.e. Does an insulated core actually make the flame burn hotter than a non-insulated core? As I understand it, it is the actual flame temperature which determines how clean or complete the combustion is, not how quickly the flue gases cool beyond the flame. Am I wrong or is there something I'm not seeing here?
I think we could safely say that core temps would never exceed the flame path temps so if anyone has been able to register and record core temperatures (burn tube or riser temps) then, in an insulated core which has gotten fully heated up, the core temps would likely be pretty close to the flame temps. Am I right?
Now with my air-cooled core, the places which were accessible rarely exceeded 900F but at the same time I know my flame temps exceeded 1250F. I have my doubts that, had my core been insulated, those flame temps would have been appreciably different. But that is just my "theory" which I am wanting to test i.e. prove or disprove.
Bruce Woodford wrote:The temperatures are precisely why I made this post and why I'm asking for specific temps recorded on J tube RMH's. Have you built and used a J Tube RMH? If so, what sort of temps does yours normally reach? That is what I'm looking for. What temps have Peter and Matt recorded on J tube RMH's? I've understood that Peter concentrates most on batch boxes rather than J Tubes.
Bruce Woodford wrote:Any specific data recorded by TESTO technology or by less expensive and readily available means to the average RMH builder is requested.
Bruce Woodford wrote:As to specific benefits offered by a properly air-cooled steel core is the ease and economy of the build of the core, if one or a friend can do a little welding, and no need of or expense for insulation.
regards, Peter
Back in 2011 I did experiment with a small J-tube core. In order to have it tested without too much work I used mild steel tube, 4" square. Please see http://donkey32.proboards.com/thread/355/small-scale-development, on the first page there's already the reason why I switched to refractories later on. The quality of the burn was much better when the steel tube was insulated but the fire ate away the steel at an alarming rate. I have to stress here that it was a small-scale experiment, just to try out what different configurations would do. A larger J-tube has a better surface/volume ratio and can burn hotter as a general rule.
At some point I used a digital thermometer with K-type thermocoupler rated for 1830º F. Down in the insulated feed tube I measured a temperature of that same level, probably it was higher than that but I took it out for fear I would destroy the thermocoupler. So one could safely say the real temperature was much higher than that. During the years, I borrowed a better thermometer and higher specc'd thermocoupler and checked a 6"batch box rocket I was working on at the time. That one showed real temperatures in the riser of 2150º F, just 40º less than the theoretical maximum of a wood fire in an atmospherical aspirated environment. There's no reason to believe a larger J-tube could achieve less than that only.
Thanks so much Peter! This is the kind of info I'm searching for. However you just mention temps in the insulated J tube but none for the uninsulated one. It is the comparison which I'm looking for. The base of the feed tube (where you got your 1830F reading is also the hottest place in my J tube but I have no way of measuring the temps there. Have you measured the temps there in an uninsulated core? At the same time as you tested the temps in the base of the feed tube, did you also test temps in the heat riser? I believe the hottest temps are reached where the oxygen is introduced to the combustion (i.e. base of the feed tube and front portion of the burn tube.) Am I right or wrong there?
Thanks again! As far as I know, you have done more specific testing, with equipment not readily available to most of us, than anyone else.
Bruce Woodford wrote:This is the kind of info I'm searching for. However you just mention temps in the insulated J tube but none for the uninsulated one. It is the comparison which I'm looking for. The base of the feed tube (where you got your 1830F reading is also the hottest place in my J tube but I have no way of measuring the temps there. Have you measured the temps there in an uninsulated core? At the same time as you tested the temps in the base of the feed tube, did you also test temps in the heat riser? I believe the hottest temps are reached where the oxygen is introduced to the combustion (i.e. base of the feed tube and front portion of the burn tube.) Am I right or wrong there?
regards, Peter
Bruce Woodford wrote:Do you know of anyone else who has the ability to accurately asses interior RMH temps?
regards, Peter
Peter van den Berg wrote:
Bruce Woodford wrote:Do you know of anyone else who has the ability to accurately asses interior RMH temps?
No, sorry about that. What you could do yourself: buy a digital thermometer like Voltcraft and some thermocouplers type K class 2 with a long thread that's temperature resistant. That sort of equipment, when chosen carefully, is capable of measuring up to 1200º C, equivalent of 2190º F. Tolerance of this combo: plusminus 2.5%.
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