allen lumley wrote:Frank R. : Good review, I especially like the idea of using wax of two different melting temperatures, in two different places in the Thermal Mass.
If this turns into a personal project, please keep us informed ! For the Craft ! PYRO AL
Marc West wrote:Hi all,
Firstly, to answer the original poster: there is an encapsulated PCM material called "Micronal" made by the German company BASF:
but I appreciate that that post dates from a couple of years ago...
I have a slightly different enquiry, and I wonder if anyone can help.
I co-own some land with a small community, and we wish to build a cobb wall on it, partly to provide support and warmth for trees like apricots and peaches. (We are in Cardiff, Wales, UK). Now, it has long seemed to me that incorporating PCM in the cobb structure would be a great way to extend the warm period at the end of a hot day. I've just read this thread and realise that paraffin wax in tins embedded in the wall may be just the thing. (Thanks to Frank R for his clear posts!)
The issue for me, then, is to find a paraffin wax that melts at the right temperature, which I guess should be in the region of 22 degrees C or so, for it to be most use for extending the warmth of the day for plants. (Anyone have a better guess?). Now, as I understand it, paraffin wax has a melting point of between 46 and 68 degrees C (variable because paraffin wax is not a single substance but a mixture of compounds [called 'alkanes'] of the form CnH(n+2), for example C25H52). So using 'ordinary' paraffin wax wouldn't be any use, because its melting point would be too high.
So how to get a lower melting point paraffin wax-like substance?
2 possibilities occur to me:
1) mix in or use some shorter chain alkanes. Ought to work fine, but looks like it will be a lot more costly than standard paraffin wax is;
2) Dissolve something into standard [inexpensive!] paraffin wax to lower the melting point, in rather the way that dissolving salt in water lowers its melting point (which is what we do to ice to make it melt when on driveways etc). Does anyone know what substances can be dissolved in paraffin wax to lower the melting point? Salt? Some other "more organic" substances that will dissolve better? I'd be happy to experiment with a thermometer and a saucepan of the stuff in a water bath, but I don't really understand how to calculate the likely effect on melting point of dissolving a certain quantity of material X into paraffin wax.
Not being a chemist, I don't really know where next to go with this. I'd appreciate any thoughts you guy may have on this. Or if someone knows of affordable off-the-shelf paraffin wax substances with melting point in the right range perhaps they could let me know.
Thanks in anticipation...
If I was going to build it myself, I would need to figure out how to do in a much smaller volume than a conventional RMH. But that can be surmounted.
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