A TRACKING SOLAR CONCENTRATOR
THE COLLECTOR
collector must be a rugged device, capable of surviving a loss of fluid, in which case it will heat to about 1200 F before its losses equal the solar energy input. It must be designed to handle the fluid flow rate and pressure to satisfy your application. The first idea that comes to mind, is to use copper tubing, perhaps attached to a flat metal plate similar to the construction of most flat plate collectors. This indeed has been tried and found unsatisfactory. The tubing cannot be soft soldered because of the high temperatures and hard soldering creates monstrous warpage problems. Mechanical attachment such as clamping fails when the copper loses its temper, and oxides form when it overheats, resulting in poor thermal connection. The plate cannot be eliminated, unless you can figure out a way to cover the entire target area with tubing and still manage to have low flow resistance. Tests were made with collectors using aluminum which simply melted and ran like molasses when overheated.
The satisfactory design that was adopted for the prototype is very easy for you to duplicate. Two plates of 14 gauge steel are sandwiched to- gether and the fluid is ran through the space between them. The heat has only a few thousandths of an inch to travel to reach the fluid. The resistance to fluid flow is very low and the design has survived many deliberate dry runs for hours at a time. It is necessarily heavier than some others we tested, weighing in at 23 pounds, but this is acceptable. The collector is built somewhat like a steam boiler with stay bolts to strengthen it, figure 28.
- Caution: It is not a steam boiler and we have made no attempt to test or prove its capabilities under high pressure steam.
The collector is intended to work in a low pressure loop, not to exceed twenty psi. If you need higher pressure, then you should seek out persons skilled in boiler design for advice.
