Re-think

The winter is approaching, its getting cold, and the particle panels are on my mind again.  Yesterday's glue's discovery got me thinking.  I've certainly encountered a number of problems over the last year or so.  There are so many variables at play it can be a little discouraging.  I've been in this position before with some of my other projects, but eventually time and experience wins out and a combination is found that works.  My hope is that this blog post will put forward a design that solves the many constraints I am faced with.  I have everything I need or it is available from a local distributor. 

Particles

I have a bunch of the 60um silicon carbonate particles as well as 40um wire mesh.   I have been worried that the silicon carbonate particles will wear the panel out from the inside, as they are abrasive.  Some readers have been very helpful in pointing out alternate particles, from glass to carbon to plastic.  The particle panels concept should work for particles that are lighter then water so long as the water flow is reversed.  This has some advantages and some disadvantages.  Right now it would be a pain, as the plumbing gets much more complicated if I want to operate as a drain-back system.  The particles would presumably be softer (perhaps plastic), making them not as abrasive.  I looked into polypropylene micro-spheres and the cost was pretty high, much more then I would like.  Floating particles are still on the table, but i'm going to continue with heavier-then-water particles.  In fact, i'm going to continue with what I started with: silicon carbonate.

Plastic

My first prototype was with polycarbonate (PC) because I could get it from a local distributor.  Not long after I discovered that PC degrades in the presence of hot water (hydrolysis).  This was obviously horrible news for a solar heater.  I then though I found the solution with polypropylene, but I could not get clear panels.  They were "milky", which I really do not like.  Polypropylene is also hard to glue and welding the manifold on the end is very difficult.  I then looked at acrylic, which seems good. However, getting the panels is a pain as I do not have a local distributor.  Acrylic is also very brittle. 

The only problem with PC is the water degradation.  This is a big problem, but perhaps I have a solution.  In previous posts I discussed the idea of circulating oil through the panel.  The idea is that a small amount of oil is put in the tank.  This oil is circulated into the panels and should stick to the inside walls.  Since oil is hydrophobic it should stick to the plastic panels.  My thinking here was to repair any damage that occurred from abrasive particle wear, but now I'm thinking it could also solve the hydrolysis problem.  If there is a protective layer of oil between the water and the plastic...should that not help tremendously in the panels ability to fight off hydrolysis?  I think it will.

My concern now is that the oil layer will trap particles, causing them to stick to the inside wall.  This may or may not happen.  If it does, its a big problem.  If it does not, then I may have my solution.  There is also a problem of what oil I use.  And just because i'm circulating an oil with the water does not mean it will stick to the inside of the panel. I may need to "pre-coat" the inside with oil to insure that a layer of oil exists to catch the oil droplets as they pass by. 

I think this strategy may pan out.  It allows me to use materials which are available commonly available and inexpensive, which is very important if this is to work.  If I could get all this working, then its possible kits could be sold that would allow home owners to build their own panels, saving the cost of the labor and allowing them to heat their homes for years for a few hundred bucks.  Thats what keeps me going.  One day it will all come together!

 

Glue

Just a quick update on a great find.  I needed some glue for another project and was recommended E-6000.  The stuff is pretty interesting.  It sticks to everything, goes on with a viscosity sort of like silicon and actually looks a bit like silicon.  However, when this stuff dries its a crazy combination of extremely tough and flexible.  This is important because I am still not crazy about how I have bonded the manifolds for the panels. 

I need to glue or weld the manifolds to the end of the panels.  For the prototype I used some acrylic plastic adhesive, which comes in two types.  One type is really just a solvent and is extremely thin.  This works if you have to bond two really flat peices together, but it turns out that the edge of the double-wall panels (be it polycarbonate or acrylic) are not really flat.  Each channel caused a little bulge.  The result is that when you try to use the solvent adhesive, it cant form a tight seal.  The other type of adhesive was more "gooey" and provided for some ability to fill in the area between the bulges.  However, it still dried very quickly which made it a challenge to get on.  It also dries fairly solid and brittle.  I've tried silicon, but it does not stick very well.  I've also tried welding, but that is really hard when the manifold material is thicker then the double-wall panel.  I can see welding the manifold on without some sort of special oven, and that would be a pain.

Enter E-6000.  I put some of it on a test piece last night, where I glued some polycarbonate single-wall to a double wall.  It went on easy.  It's a bit noxious, but nothing even close to the solvents I've used.  The instructions say to apply some to both surfaces and wait for 2-10 minutes before pressing them together.  That is the perfect amount of time.  Not to short to be difficult, not to long to be a annoying.  Today I tested it, and it was an incredibly strong bond.  I had to resort to extreme force while prying the piece off.  I could not remove the piece when I tried to pull it off. The glue remains flexible, which means that the panel itself will be more durable.

Some of its stated features:

• Does not become brittle in cold weather, can bond items subject to vibration.
• Excellent chemical resistance to water, dilute acids and dilute bases.
• Can be submerged in fresh and salt water after complete cure.

I cant believe I'm excited about a glue.  But seriously...this could solve a big problem.  I want to figure out how I can build these panels so that anybody can build them at home.  I think i'm one step closer.