Ball-Shaped Particles for Solar Thermal Panel

What does Alex think of your idea?

Heavier or lighter than water? The weight of water has been discussed on this forum here, and we cannot seem to agree. You will have to define this a little better!

"What does Alex think of your idea?" I quote from Alex' latest email: "Thank for the info and taking the time to help out. (…) the internal resistance of the panel limited the flow. (…) if the particle was just slightly more or less dense than water then its sink/float rate would go down (…) and we'd just need (much) bigger particles." Summing it up: Despite their inherent minimum surface-to-volume ratio ~as opposed to flakes~, ball- or potato-shaped particles are required to prevent clogging of the outlet filter, as flakes will, thus decreasing flow rate and increasing pressure inside the panel. Large numbers of SMALL particles are required only to increase the overall heat transfering surface. Either barely floating or barely sinking particles could be used; they must be kept from floating or sinking by a relatively small flow of water. (The direction of the flow would need to be reversed.)

I am a little confused... some members will not be surprised at that.

Speaking of the particles you seek, in your question you say "Weight is not an issue as long as they are either heavier or lighter than water". This sounds to me like neutral bouyancy is undesirable. So, very fine sand might be in the running for consideration.

Citing your information from Alex, "Either barely floating or barely sinking particles could be used; they must be kept from floating or sinking by a relatively small flow of water." This sounds like the particles should be neutral bouyancy, or very close to neutral. If the water contains a large amount of dissolved gas, then very fine sand might still be in the running if nucleation can be counted on.

We really need you to tell us more. An open discussion will give you much better results.

Well...

I went back to your referenced page and had a closer look. I wish I had done more and better due diligence in the first place.

Just try some fine sand. It will work, or it won't. There is no sense beating this issue any further.

Maybe somebody else has another idea.

Just try some different stuff, and see what works.

Fine black ball-shaped sand particles? Almost sounds like "unobtanium" to me. Can you be more specific and indicate where/how these can be obtained?

Yes, you're right, an open discussion will probably give better results. Maybe I just tried too hard to be concise. The issue here is solar heat collection and -transfer by dark particles suspended in water inside an acrylic panel. The particles are trapped between sieves; cold water flows in at one end, absorbs heat from the particles and flows out at the other end. Thus far Alex used flake-shaped silicon-carbonate particles, which is logic for reasons of surface-to-volume ratio but apart from causing crazing on the inside of the panel, they also tend to clog the outgoing sieve, thus raising the pressure inside the panel and decreasing the flow rate. Since I questioned the use of these particles and Alex explained that this was mainly for economic reasons I offered to help in finding alternative particles, also by posting the question on this forum. So actually we're just looking for low-cost alternatives, e.g. black powdercoating particles, but even better solutions may be available. My reluctance in providing more information is mainly meant not to discourage "out-of-the-box" thinking concerning particle behaviour in water, buoyancy, heat transfer etcetera. By the way: neutral buoyancy particles might enable horizontal positioning of the panel, perpendicular to the sun. Would you agree? My personal interest is in finding low-cost heat storage opportunities for the (hybrid) solar dryers for fruitdrying I'm trying to build and deploy in West Africa. Hopefully this satisfies your question. And I hope for many helpful contributions. Kind regards, Fred.