Need advice on this heating system, thanks guys

[syryanyang]

Hey guys 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?
If you reckon this will work, then I will be looking for the material of the two layers
The polymer will need to be transparent, low solar radiation resistance, high heat resistance and low conductivity
The metal will have to have a shinny surface that absolves solar energy but a relatively low conductivity.
Anyone that gives me any insight would be much appreciated.

 

[IRstuff]

Why are you re-inventing the wheel? The fact that you think the solar energy absorbing layer should be "shiny" is a smidgen troubling, I'd say.

TTFN
faq731-376

 

[EnergyMix]

Not an engineer? Homeowner? What part of the world makes a difference don't ya think?

 

[syryanyang]

Yes I am not a professional engineer. Im with this community trying to help.people livong in.poor village with no supply of hot water. Yeah.i miswrote that, it should be dark/black surface.
what do you think is the “wheel ” for my situation

 

[DRWeig]

Your idea should work. It is similar to a common solar collector. Collectors are usually made of glass, not plastic.

Safety first: Be careful of water that may get too hot. Beware of high pressure if your system is not vented or relieved.

I think there are clear acrylics and polycarbonates with good radiation transmittance, fair thermal resistance, and good resistance to deterioration by UV radiation. I am not as good at choosing such materials as many in these forums, so maybe you will get some other suggestions. My experience has been with visible-light gathering products that are used outdoors, and also with windows for buildings. That is where I have run into the sort of plastics that might work. UV resistance is important as well as high temperature.

I would consider a container that is rectangular instead of a cylindrical drum. Glass will work for this style, no bending or curves involved. Expose as much surface area to the sun as possible. It would be the shape of a book, with the cover facing the sun. Tilt the larger face approximately equal to the latitude of your area, facing due north if south of the equator or due south if north of the equator. Insulate the other five sides of the box well. Include a means to cover the sun-facing side with insulation at night.

Another way that do-it-yourself solar people accomplish this is to heat the water coming in to the tank, and dress the tank as a well-insulated storage vessel. That might be simply running the cool water through a long black hose or pipe that is also exposed to the sun.

Experiment. Build small ones. See what works and what doesn't. Come up with ways to improve. I'm going to do what is probably a first for the eng-tips forums. I will cite The Mother Earth News as a reference. That magazine has had many articles and drawings for low-cost solar water and space heating over the years. It caters to incurable earth-lovers (like me). Give it a search.

http://www.motherearthnews.com

Best to you,

Goober Dave

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[willard3]

You are going to have to become familiar with thermodynamics and heat transfer to quantify any of your ideas.

A web forum will not teach you what you need to know.

 

[IRstuff]

There are TONS of stuff on the web, which you should refer to, such as:

http://www.azsolarcenter.org/tech-s...solar-hot-water/solar-hot-water-a-primer.html

http://www.builditsolar.com/Projects/WaterHeating/water_heating.htm#Batch

TTFN
faq731-376