Heat Transmitting Concrete

Not much to go on. Is it F or C?

I've used this before, it may be too expensive for you, but it's an excellent conductor. (Not an endorsement)

Sauereisen - Adhesives and Potting Compounds

Oops. I didn't see that you had already sourced Sauereisen.

And after we've just been having this long discussion about plagiarism, too.

Never mind, just shows great minds think alike.

_{Hope you are doing well.}

Look into radiant floor heating. Geothermal heating systems using hot water piped from hot springs use special cement to maximize effeciency of radiation

Do you mean concrete or cement?

On the chance you do mean cement, take a look at Sauereisen.

Have a look at this type of concrete. It is used in thermal storage industry.

http://www.docstoc.com/docs/34389193/CONCRETE-STORAGE-FOR-SOLAR-THERMAL-POWER-PLANTS-AND

In India they add iron powder (specifically made as a concrete additive) to the concrete. It improves thermal conductivity and gives a hard wearing surface for iron wheeled trolleys.

Can you tell us more about your application? Concrete is not a super insulator--I'm wondering if you really need better heat flow than you'd get from just ordinary concrete?

Well I am thinking of building a solar water heater panel that is not only cheap to produce, but will be the storage unit, roof panel, and no value on the scrap metal marked. I am living in Namibia a country with one of the highest sunshine values, but yet still everyone is using fossil fuels to heat water. Building them out of any value material they will end up chopped to pieces, and sold to scrap dealers. I thought of using rather large concrete/cement panels like 3 off 3.6 meters by 2.4 meters for an all purpose roof structure. At the moment most of the shacks (if I may call them so) are build from galvanized sheet metal with no insulation properties. I thought of using ½ inch thin wall tubing spaced 120mm bound together with chicken mash wire 4 layers and then pestered / cast concrete to about 1 inch thick. This should give me a self supporting panel over the span of the roof of an standard shack. Done some testing and it works quite fine ( on a 2.4x1.2 Panel) except the sheet gets lots of hairline cracks and the water absorbs the potential heat to slow. The panel reaches 65 deg C quite easy but the water dwindle around 38 deg C but then keeps it that way for an hour or two after sunset.

Thanks for the response! Interesting idea.

Have you tried a dark coating on the concrete (like black paint for a first test)?

Does it ever freeze in Namibia (now I'll need to look for Namibia on a map)--my concern is that freezing and hairline cracks will probably lead to fairly quick deterioration of the concrete--another reason to consider a (dark) coating like paint.

I'm also wondering if the problem is slow / low conductivity of the heat, or some other problem (like--I don't know, heating too little volume of water?)--maybe the system would work better if you increased the water flow rate and achieved a larger volume of water at a lower temperature , maybe aiming for a larger volume of water heated to 38 degrees C rather than 65 degrees C?

Ahh, you didn't mention a storage reservoir (for water)--do you have one? I forget--did you mention in an earlier post that you were hoping to use the concrete as the heat storage medium? I'm not an expert, but that doesn't sound like a lot of storage, and it doesn't surprise me that the water cools down to 38 degrees (or lower) fairly quickly after sunset.

As a test, could you rig up your system of tubes and mesh on a roof (or on the ground) and see what the performance is without any concrete? (Maybe painting the tubes and mest black as well? (I'm trying to think of a way to test whether it is the conductance of the concrete that is the problem. If your results are pretty much the same without concrete, then I'd think that the conductance of the concrete is not the problem.

And, if the concrete was intended as the heat storage medium, without the concrete the performance will be worse--to me, pointing to the need for a water reservoir for heat storage. For something like that, unlikely to be cut up and sold for scrap, you could cast a concrete reservoir and install some form(s) of insulation around it.

I like your idea. I wonder if, at some point, you could cast water channels inside the concrete without the thin wall tubing, thus saving that cost. Hmm, only dumb ideas come to mind--laying bamboo in the concrete to form the channels and then burning it out--or not.

Good luck!