9 ms·
I suspect it's because the thermal conductivity of sand isn't that great. If you've got your working fluid running through pipes embedded in hot sand, the syst
by regularfry 3y ago
I suspect it's because the thermal conductivity of sand isn't that great. If you've got your working fluid running through pipes embedded in hot sand, the system is likely bottlenecked on getting the heat energy from the main body of the mass through the cooler sand closest to the pipes.
Do it the other way and the enormous surface area is working for you, so you can presumably get the energy out arbitrarily fast (or, at least, that's no longer the bottleneck).
- regularfry 3y agoThe thought occurs that if that is indeed the problem, you could attack it by mixing a metal in with the sand. You'd still get the thermal mass, but conductivity would no longer be a problem as long as it had been in a liquid phase at least once.
- zdragnar 3y agoThe problem isn't so much the sand, it's all the air gaps between the grains of sand. Adding metal won't help any- once it gets to a liquid phase, it'll sink down, or if it doesn't stay liquid long enough, will just trap most of the air in it. Edit: you'll also want to keep oxygen out of the environment in the liquid phase. Depending on the metal you use and the exact makeup of the sand, you'll wind up with some materials that are often used in refractory cement- aluminum, oxygen, and silicon will do the trick and absolutely ruin the effectiveness of your heat battery.
- regularfry 3y agoThat's what I was getting at. Fill the air gaps with metal.