[Mobile Master Tech]

Thanks, Jeff!

What I have found so far:

Some work by Heinz & Streicher showed that over a 15C temp swing, SAT with just enough additives/extra water to stabilize and prevent supercooling (5% or less additives, and 2-3% extra water) held 7-8x more heat than water alone. Adding graphite, etc to increase conductivity reduced this to about 5x of water. Others said more than 5% extra water started to significantly limit latent heat storage.

I'm not worried about improving conductivity. My PCM containers will have 3.5" cross sections and the fastest I could use up that much heat is over an 8hour period. I'd rather have more storage capacity.

Everybody seems to recommend 2-5% of a thickening agent to prevent phase separation-bentonite, fumed silica, superabsorbent polymer like in diapers (SAP), carboxymethylcellulose like the food additive (CMC) are most common, but everything that could be put in a kitchen sink has been tried. They also seem to recommend up to 2% of a nucleating agent or combination of nucleating agents to prevent supercooling, and again nearly everything has been tried, including silver nanoparticles. 3% extra water helps prevent crystallization.

Pure SAT with no nucleators or thickeners can store heat indefinitely, and yes, that's probably the formulation in the heating pads. Great seasonal storage idea, but I think I like dirt better for that, as it would be expensive to only cycle a few times per year.

CMC seems to work best as a thickener, and strontium sulfate seems to work best as a nucleator, demonstrating 0-2C supercooling. Boy, lots of patents and choices. What works best, though?

My goals: additives that are cheap and common which make SAP work indefinitely or at least 1000 cycles with little degradation, backed up by practical experience.

Hope some others chime in as well!