Win a copy of For the Love of Paw Paws this week in the Fruit Trees forum!

Peter Peterson

+ Follow
since Aug 03, 2013
Apples and Likes
Apples
Total received
2
In last 30 days
0
Total given
0
Likes
Total received
6
Received in last 30 days
0
Total given
0
Given in last 30 days
0
Forums and Threads
Scavenger Hunt
expand First Scavenger Hunt

Recent posts by Peter Peterson

Thanks for the answers!

Yes, I supposed this was magnetite. Actually I thought you used it at that place because of its good thermal conductivity. This would make sense, except the two bricks near the door. But ok, you say and I believe you, the disadvantage because of the high thermal capacity is more important.

I found a ceramic fibre tube even on ebay.

regards
Peter
4 years ago
Some questions addressed to Peter van den Berg:

Dear Peter,

I watched several of your videos in the internet and find them very interesting.
Some questions remain:

1. Please have a look at the attached pictures. One is from Sketchup and one from the corresponding video (“Accumulating kitchen range”). I marked some bricks. They look different from the others. What are they made of? Why did you use them at this place, i.e. what special properties do they have? Are they commercially available? Where?

2. In one of your posts at Permies you say: “... a round ceramic fibre tube one. The bricks are there only to fix this tube in place.” Can you tell me (us) a little more about this tube? Where to buy it? I am in Germany this days.

3. Did you ever use bricks of Iron oxide (magnetite, hematite or something like this) in construction of masonry heaters? If yes, why, what are they good for?

Thank you very much in advance for answering these questions!

Peter
4 years ago
Hi Aldona,

I am quite often in Germany because of friends and business partners. That's why a thread of this forum announcing a workshop in Germany is still in my mind. It was some month ago but may be its interesting for you, may be you can contact this people.

https://permies.com/t/28021/rocket-stoves/Workshop-Germany-Sept#221441

Peter
5 years ago
Hi Martin,

Could you please tell us that source “for buying peltiers elements at reasonably prices” ?

Some thoughts:
the speaker in that video mentioned in this thread says at a point “it's for free”. He means the electrical energy produced by the thermo-electric-generator (TEG). I guess he did not mean this too literal because it's wrong. True is, a part of the thermal energy is transformed into electric energy, i.e. this part of the heat is not longer available for heating your home – so electricity it's not for free.

Looking closer: A certain amount of the heat produced by burning wood is traveling through the TEG from the hot side to the cold side. A very small part of this energy (something like 1%) is transformed into electricity and 99% is released on the cold side to the cooling agent. You want to use the outside air for cooling. In this case 99% are lost.
This is still ok if you use a small TEG, i.e. the amount of heat “used” by the TEG is very small compared with the amount produced by the RMH. For instance the ventilator placed on top of the barrel in that video will not cool remarkable the barrel. But if you really wand to produce electricity for your whole house you should at least use the heat released by the cold side of the TEG e.g. for preheating the fresh air before let it enter the combustion chamber.

The converted ratio of energy depends on the temperature difference between the hot and cold side of the TEG. The 99/1 mentioned before is just a guess. But the real value will not be to far away from that.
I am (and I'm sure I'm not the only one) curious about your progress. Keep us informed!

regards
Peter
5 years ago
John: Thank you for answers and for the interesting link.

I found a lot of clay here nearby but only the red/brown one. good for terra cotta. That's why I am thinking about mixing it with pure Kaolin.

Yes, cracking during heating or cooling is a very complex process. It is an interaction of the coefficient of thermal expansion, the thermal conductivity, tensile ductility of the work piece and of course how fast and uniform you heat or cool the workpiece. Many electrically heated kilns offer the possibility to precisely program the temperature over time curve. With a wood fired kiln the operator has to have the experience how to control temperature by adding more or less wood or open one or the other air intake but if you operate a RMH you just put some wood in the feed opening and light it up and add more and more wood. The combustion chamber and the heat riser will heat up quite fast and probably not very uniform. May be this is the reason why many people build the combustion chamber out of bricks i.e. relatively small pieces of clay. The chance that such a small piece is heated uniform is much higher than for a large piece (e.g. the whole chamber). And if in spite of this a crack appears, it will not go through the whole wall, but will stop at the boundary of the brick.
I do not know how for instance the “dragon heater” people avoid cracks in the cast large components of their combustion chamber.

regards
Peter
5 years ago
John Elliott: Excellent idea to open this thread.

Three questions regarding thermal stability of clay:
1. As more Kaolin (Al2 Si2 O5 (OH)4) clay contains as higher is the melting point. Is this true?
2. What about cracking during heating or cooling? How to avoid this? Is this somehow linked to Kaolin content?
3. If higher Kaolin content is better, can I simply mix any found clay with pure Kaolin to make it more heat resistant? Pure Kaolin is not cheap but you can buy it as a white powder.

One question regarding recognizing fire clay:
4. Is there an easy way to determine if a certain clay is fire resistant, if you do not have a kiln to simply heat it up and see how it behaves? This is probably the same question as: Is there a simple way to determine the Kaolin content of clay found in nature?

regards
Peter
5 years ago
Allen: Yes I heard about this. If the bubble size comes in the range of the free path length of the air molecules, the thermal conductivity drops tremendous. But this is nothing for us poor D.I.Y. guys
5 years ago
Paul Carter: thank you for the link!
Cindy and Allen: thanks for your answers!

Allen: I agree with you regarding the video of Rob T. I stopped it at 55 sec and you are right.
I also belief that a heatriser made of fire bricks wrapped with rock wool will last for long time because the rock wool will not be directly hit by the flames, as you say.
In question no. 1. (see my last post) I meant the flue gas flowing downwards between the heatriser and the barrel. At this place flue gas is not hot enough to melt rock wool.

Why did I ask question no. 1. ?
Rock wool is thermally insulating because of the air trapped between the rock fibers. The fiber itself is not insulating. It has a similar thermal conductivity as the rock it was made of. The task of the fiber is to prevent air from moving round (convection). Moving air would transport heat from hot surfaces to cold ones. This means it would be better if the layer of rock wool would be enclosed in an airtight coat to prevent any air going in and out the rock wool layer. That's one of the reasons (besides reflection of thermal radiation) I drew an outer layer of aluminum foil in the sketch. Ok - this effect might be small. If the rock wool layer is thick enough there is enough air in the middle of the layer that can not move anywhere. Regarding the heat riser of E+E you mentioned, on one side of the rock wool layer there are the fire bricks, so this side is closed. Only the opposite side, where the wire mesh is, is open to gas exchange that lowers insulation. In practice this might not cause concern.

best regards
Peter
5 years ago
Pack:
you wrote:
“Think I should add some refractory cement to my clay/sand mortar?”

You find in the Internet examples where people mix clay with cement (e.g. [youtube]http://www.youtube.com/watch?v=7ANMXGrxgnE)[/youtube]

I wonder if the cement preserves its properties if it is mixed with clay. If not, it is wasted. But it is difficult to say something without knowing exactly what type of clay and cement is used and what's the ratio. There are so many materials we call “clay” or “cement” or “firebrick” or “fire cement” etcetera. In addition to this, in different countries different terms are used for the same thing. Internet discussions have an inherent problem, you never know what exactly the other means.
The only you can do, try and tell us the result. Tell us as precisely as possible what you did so we can learn how to do it or how to not do it.

Allen: two questions
1. The RMH you mentioned build by Erica and Ernie. Is the rock wool round the heat riser held just by woven chicken wire fencing? Does this mean the flue gas can enter the rock wool?
2. In an other thread you wrote about castable core units (I guess you mean combustion chambers) that burn at 3500 F. Do you know from what material are this made? Is this suited for D.I.Y.?

Cindy: What material is used to cast the “Dragon heaters” combustion chamber? Is this suited for D.I.Y.? Or is this secret? I would understand if the recipe is not public. There was probably a lot of work necessary to find it.

regards
5 years ago
Allen: here is the link for the video showing how rockwool behaves as insulation on a heat riser.

I do not know how some people manage that the video appears directly here in the posted text.

What do you think about a heat riser like in the attached drawing? It is just an idea, I did not test it. It is cheap and should work fine. I am not sure the aluminum foil will last for long but something has to prevent mixing of the flue gas with the air inside the rockwool and save rockwool from being blown away.
5 years ago