Polymer with low solar radiation resistance, high heat resistance

[Syryanyang]

I'm an engineer student and I'm trying to build such a solar heating system that it is drum with two layers, inner one is a metal (aluminium alloy I'm thinking) water container and outer layer is made of polymer, with air gap in-between. When suns come out, it radiates through the polymer and on the metal layer, heats up the water inside. The air gap severs as an insulation. Could someone with more experience give me some advice on whether this will work?

 

[chill_factor]

I'm an engineer student and I'm trying to build such a solar heating system that it is drum with two layers, inner one is a metal (aluminium alloy I'm thinking) water container and outer layer is made of polymer, with air gap in-between. When suns come out, it radiates through the polymer and on the metal layer, heats up the water inside. The air gap severs as an insulation. Could someone with more experience give me some advice on whether this will work?

why put polymer on the outside? the most common cause of environmental polymer degradation is UV radiation oxidizing the polymer chain ends which then become highly reactive. typically they become brittle and discolored.

if you want an outer covering to prevent convection from carrying away too much heat the best thing to do is commercial solar grade glass since it is thermally robust, doesn't degrade to sunlight and is pretty cheap. also don't take my word for it but i believe its much easier to use pipes instead of one big drum of equal volume since its cheaper to buy pipe than to buy a big steel tank, there's more surface area for radiative heat transfer, and i don't think the extra convective surface would matter with the glass covering.

i've seen some solar heater designs that are just a row of pipes inside an evacuated glass box.