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How hot does the flame path in a J Tube have to be to qualify as an RMH?  RSS feed

 
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Some have intimated that an air-cooled steel cored J Tube heater is "really not a rocket mass heater" at all! But as far as I can tell the temps that are achieved in a steel cored, air cooled J Tube are just as hot as any other J tube RMH which is fully insulated. 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)?  Where would temperature readings need to be taken to determine this? At the bottom of the heat riser? Half way up the riser? At the barrel top?  I'm interested in learning so.... what temps have you other J Tube builders recorded with fully insulated, non-insulated or air-cooled cores? Where in the core and how did you measure your temps?   I have demonstrated temps in excess of the melting point of aluminum from the base of my heat riser to at least 2 feet up the riser and have had barrel top temps beyond a 67"long riser up to 800 F.  Is there really any reason to doubt that such a J tube is really an RMH?
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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.
If  monitor your emissions with a Testo,you might show similar results to those of a insulated non-metallic J-tube.
Or you might not.
Efficiency might be measured by weighing your wood,checking it for moisture content, and somehow recording the heat output.

If your J works for you, then it's good enough,for you.
If you want to convince the community, you'll want to meet or exceed the testing that Peter and Matt have done.
Matt's designs have differed from "orthodoxy",time and agsin, but he backs them up with performance data.
I'm pretty sure some if his stoves are less efficient or clean, but make up for it in lowered expense, or reduce difficulty of the build.
Or perhaps they offer more utility, like his glass topped stove.

Does your design offer something extra, beyond what an "orthodox" insulated non-mettalic J-tube does?
 
Bruce Woodford
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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.



Hi William, 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.

Any specific data recorded by TESTO technology or by less expensive and readily available means to the average RMH builder is requested.

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.

Thanks!
 
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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)?



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.

Is there really any reason to doubt that such a J tube is really an RMH?



As to this question, I say call it whatever you want. Names are just names. We make them up to group similar objects together. Unless it's a trademarked or technical term (like glyphosate), the interpretation is up to the eye of the beholder
 
William Bronson
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I have only built L's and pocket rockets.
Matt has made and I believe tested J's.
Peter has also built them, I believe, but I'm not sure if he was using his Testo back then.
Of course,both of these fellows have concluded that insulation and the resulting high tempature are needed for a clean burn.
Matt is even more a fan of insulation , whereas Peter is not as interested in insulating the firebox.
I'm only going by what I understand of their writings.
If you can make it to a gathering like the Jamboree,I'm sure they would help you test.
I can see the appeal of steel to some one who welds, but even though I'm a plumber, electrician,baker and candlestick maker, I don't weld.
I get going your own way, my designs all center on what I can get cheap,easy,and local.

Keep plugging away, you might have the next P-channel,or sidewinder. The field of rocket stoves is wide open.

 
Bruce Woodford
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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.

 
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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.


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.

In short: the insulation around the steel tube made a world of difference, combustion quality-wise.

Now your air cooled steel tube: in my view, it is what you call it, air cooled. So it can't be as hot as the insulated refractory, otherwise it would spall away in no time. You tested it with thin aluminum cans inside the tube, some of the metal was left over, so the temperature didn't go over meting point otherwise all the alu should be in a puddle on the tube's floor. Melting point of aluminum is, according to Wikipedia, 1220º F, a mere 930º less than the values mentioned above.

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.


Please read the above-mentioned thread, 6 years ago I recorded a marked difference between insulated and uninsulated steel.

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.


You can call your heater any name you fancy, whether it be rocket heater or spaceship hyperdrive core. It is plausible to say it won't be as clean as an insulated refractory core, even when there's no visable smoke. On the other hand, it is easy to make, fun to experiment with and it will survive a fair bit longer than an insulated equivalent. Count your plusses and minusses, and see what aspect is more important to you. But please don't mind stubborn people like me, that want to reach for the highest temperature, efficiency and cleanest burn.
 
Bruce Woodford
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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.

 
Peter van den Berg
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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?


I didn't temperature test uninsulated cores. But at the back of my mind I seem to remember that I measured the riser of that same small steel core. And since you had some approximate numbers for your riser, achieved the empirical way without equipment but with aluminum cans instead, I decided to give it a go. I had to delve into my rather sketchy and chaotic notes from years ago, but finally I opened the right box and there it was. About two months later than the rather scary measurement of the feed tube I tried it again, both the feed and the riser this time. The feed happened to be the same story as before but from the riser I could get accurate numbers. Hottest point about 4"  from the tunnel floor and in the middle of the riser I recorded 1019º C, which is 1870º F. Compared to the melting point of aluminum at 1220º F this is quite a lot more. A bigger J-tube is likely to reach higher temperatures, as I mentioned earlier.

And yes, the hottest parts are where you think these are located, most of the time. Mine was constructed a little differently and the tunnel end just before the riser heated up to cherry red in no time. I have to add, its refractory successor could reach that stage as well but it took a while longer to get there.

In my view, there's not a lot more to be said about this subject. An uninsulated core which is also equiped with cooling fins doesn't run as hot as an insulated one, built of whatever material. Logical, it's cooled, isn't it? Whether or not it runs as clean is another matter, this can only be settled when there are test numbers available, aquired in the same way as others so it can be compared. I know how difficult it is to optimize a combustion core of whatever construction, the chance that one could hit that best performing configuration out of literally hundreds of possibilities is very, very small.
 
Bruce Woodford
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Thanks so much Peter! That's half the info I'm seeking. Great temps!

You are  right that a cooled core will certainly run cooler but I'm trying to learn how much cooler.  I don't know what the temps were in the middle of the flame path at the base of my heat riser/top of the burn tube. All I know is that they exceeded the melting point of aluminum less than a minute after I started the fire! That's when the first couple of cans fell! So I'm sure it got much hotter than that later on, nor did I have any way to make sure my crude test cans would stay in the middle of the flame path (the hottest place).

Do you know of anyone else who has the ability to accurately asses  interior RMH temps?
 
Peter van den Berg
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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%.
 
Bruce Woodford
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Thanks so much for this info, Peter!   I do have a cheap digital but its limit is about 1000F. Which is OK for checking external temps but useless for even checking the base of the feed tube!

I'll check these out.
Bruce
 
Bruce Woodford
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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%.



Peter, I have found on Amazon a Type K class 2 thermocouple rated up to 1300C or 2372F     https://www.amazon.ca/Yeeco-Quality-Thermocouple-Temperature-detector/dp/B00XJB4DYQ/ref=pd_cp_328_4?_encoding=UTF8&psc=1&refRID=7RREVD1MBMTK87A7QGBR

and a digital thermometer rated for the same temps https://www.amazon.ca/Signstek-Channel-Digital-Thermometer-Thermocouple/dp/B00IZXOLEA/ref=pd_cp_328_2?_encoding=UTF8&psc=1&refRID=SCNAC78DJAN6APPQ0VPZ

What do you think of these? Could they be helpful to other builders of refractory J-tube rocket builders as well?  I have thought of installing one in the base of my heat riser to measure temps of the flame as it begins to ascend.

What would be your thoughts and recommendations?

Bruce
 
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I think you can get this one that has 4 higher temperature range thermocouples (1372C/2501F) with it for around $35 Canadian...  Search the brand and model on Amazon.ca.

Perfect-Prime TC41, 4-Channel K-Type Digital Thermometer Thermocouple Sensor -200~1372°C/2501°F , 20 x 4 Data Log Storage Function https://www.amazon.com/dp/B0142HFA06/ref=cm_sw_r_cp_api_dcl0zbGH8HYYQ

Or for REALLY high temp (2200C/3992F) non-contact testing:

Perfect-Prime TM6899, High Temperature -50 ~ 3992°F Infrared Laser Thermometer w/ K-Type Clamp https://www.amazon.com/dp/B06Y27QXGH/ref=cm_sw_r_cp_api_5fl0zbSG0EV8Y
 
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