Two RH's, drastic flue temperature differences - Why and How?

Hi,

Below are a couple vids showing two rocket heater designs showing temperature readings at the flue exit.



And



Both are similar in design for the rocket heater stove minus the heat flue loop (MH loop) on the first one. The first modified in his original design (see video below for his original design which includes a flue loop)




You'll notice if you watched both the temperature reading videos that there is a huge difference in the end flue temperatures, over 200 degrees.

My thought would have been that the first design would have produce a higher flue exit temp than the second since it is directly off the tank, but it is the second heater with the insulated flue heat loop that had the higher temp.

My question is... Why? And How is the temperature so low at the flue stack exit on the first design on a full burn?

Trying to understand why there is such a drastic difference in the temps, let alone, how he's getting such a low temperature reading on the first heaters flue at the wall.

tia,
- chase -

Chase, pretty simple.

The thirst thing is not a rocket mass heater, but a POS!

No insulation in the heat riser, but also no gathering of the heat in the mass after the heater. So you're not comparing the same things. He's already had problems with spalling of the metal heat riser. That build is Doomed! Oh, i forgot, with a slanted feed tube, which is known to give sub optimal results!

While Matt's build is a rather conventional rocket mass heater. An 8 inch J tube with a mass behind, gathering the last remanents of the heat, up to a certain point. Matt is a member here and at donkey's site.

A properly tuned RMH, with a chimney behind should be able to work with flue temps in the 80C° to 60C°

Hope this clears things out!

Hi and thanks for such a quick response.

Also thank to the mod for correcting my YouTube links so they would show.

Also noted, I posted the wrong second temp reading video and it was too late to edit the correct one in. So here is the correct video showing the temperature readings being taken for the second heater (an RMH)



As for your response, I believe both are insulated inside the tank. Going to check his construction vid on the first design....one second here... and yes both designs have an insulated riser.

Here is the first stove being disassembled for damage inspection.



Which by the way, he stated in one of his comments, he upgraded the materials used and the stove is doing fine now.

So since both have similar designs from what I can see on the main feed and riser and tank portion of the stoves, and only the second has a flue loop, why is the temperature reading so drastic a deference?

He is close to 285 degrees on the second design. (Unless I'm seeing it wrong and he is taking the temp reading somewhere different than the end of the flue. It's (the video) somewhat blurry when he shows the connection. But it looks to be close to the wall exit.

tia,
- chase -

The metal stove's readings are in degrees Celsius, while Matt's are in degrees Fahrenheit. 60 C at the stovepipe entering the wall equals 140 F. Not so much lower now, is it?


I didn't see Matt's video before commenting... yes his stack temp is high, higher than you would want going into the chimney. I wonder if he had too small a mass run when he did this? I know when he rebuilt the core from J-tube to batch, he extended the bench a lot.

Glenn Herbert wrote:The metal stove's readings are in degrees Celsius, while Matt's are in degrees Fahrenheit. 60 C at the stovepipe entering the wall equals 140 F. Not so much lower now, is it?

Well now... that does explain a thing or two.

No need to explain how I feel like such an dumb ass for not noticing that to begin with... (sigh)

And here I was getting somewhat excited at the prospect of a flue temp of only 60° F... (for what I had in mind)

Thanks for shining the light on that oversight.

- chase -

Ok, Robert Gisolf's heat riser is insulated. I didn't thing this was possible with such a tiny tower. But he used something like superwool, and a "metal heat riser"

Anyway, you can have many cases, for temp differences. Either you have a perfectly running rocket without mass going to the stack directly, and it will draft a lot, releasing it's energy faster than another one. Or a crapy rocket implemented th esame, but not burning as hot.


But on a mass system, when the mass gets closer in temp, to the gases inside the flue, heat exchange goes at a slower rate, thus giving higher flue temperature.

While, when it's cold, a lot of heat exchange happens between the two, giving very low flue temps. Sometimes stalling the system. The cooled gases can't go up the chimney.

A difference in top and side gap with the barrel also gives a different heat exchange scheme, up to a point that i would say, making two realy identical rockets is complicated.

Chase : This is easy mistake to make because of a common history going bak over 35 Years ! The mystery Wood fired heater appears to be a highly modified version
of the Aprovecho Institutional (Cooking) Stove (I Think )

It would also have much in common with Erica Wisners Cooking/Frying stove that was debuted at the first RMH workshop about 16 months ago ! While it can be called
a Rocket Stove, it has been modified from the original to try and achieve higher combustion temps and efficiencies, This is the reason for its metal component failures!

I created a link to let you see how the original Aprovecho (cook) Stove is still being made, so you can compare them it seems a close fit !

Link below :

https://www.youtube.com/watch?v=VdhLWMW7IXA&list=PL4F97B69F2748D32A

For the Good of the Craft ! Big AL