Sand as burn tunel insulation?

[satamax]

Hi everybody.

Well, i was wondering. Would sand be good for insulation around the burn tunel? Well, that's the way usual pizza ovens are "insulated" on top. But they let heat sip through a bit. I'm wondering up to which point i could heat the bricks or mass which would contain the burn tunel this way. I know vermiculite being a good insulator, the surounding mass would not heat as much. But with sand, the burn tunel would not be hot enough, may be?

What's your opinion guys?

Thanks a lot.

Max.

[Vortex]

I was camping once on a beach and wanted to bake some potatoes but didn't have any aluminium foil, so I improvised and put the potatoes in the empty baked bean tins and filled the remaining space with sand and then put the tins in the embers. I was amazed to see the sand do a rolling 'boil' just like water.

[peterberg]

May 28, 2013 8:33:14 GMT -8 satamax said:

Well, i was wondering. Would sand be good for insulation around the burn tunel?

Sand will retain heat, it's not insulative. The finer the sand, the more heat it will absorb.

[satamax]

Well Peter.

Yes and no! The sans itself, if it was monolithic, would be a good heat transfer media. But there's the air pockets in it. www.engineeringtoolbox.com/thermal-conductivity-d_429.html

So it's a bit of both worlds. I can always make a metal box, a bit bigger than the latest easycore i've drawn, and fill that with vermiculite. Then pile up bricks around it. But finding the right point between enough insulation and too much is tough ;D

[peterberg]

Max,
I've browsed the engineering toolbox. Vermiculite is 2.5 times more insulative as compared to the coarsest sand, and 4.3 times to very fine sand. Perlite is 4.8 and 8 times better than sand.

Ernie and Erica Wisner are considering a layer of 2" of perlite suitable in a rocket mass heater, 3" when using vermiculite. How wide should the insulation gap be when using medium coarse sand to obtain the same insulation value? Let's say a little bit more than one foot?

Too much insulation isn't possible, too little is not good, at all. You should know that, don't you?

[satamax]

Hi Peter.

Thanks a lot for your reply. Blady sand, not good for anything then. I was hoping i could reach a happy medium between keeping the whole lot of heat in, and letting seep a litle throuh, to warm up some mass around the burn tunel.

Thanks again.