Glück Auf is loosely translated as "good luck to us all".

Wednesday, June 1, 2011

The Rotating Solar Boiler

Back in 2005 a fellow named Jeroen van Luijtelaer did his Master Thesis on the the Rotating Solar Boiler at Delft University of Technology in The Netherlands. You can download his thesis paper from http://www.builditsolar.com/Experimental/RSB/RSB.htm.


Several prototype boilers were build using different materials, but all boilers shared the following basic design components:
  • An absorber tube that holds and heats the water
  • A transparent cover that holds and heats the air
  • A reflector that reflects the light onto the boiler
  • A motor that rotates the boiler at about 60 RPM
According to the thesis paper, convection significantly reduces the efficiency of conventional solar collectors. The rotating solar boiler rotates at about 60 RPM in order to prevent convection. The centripetal force pushes the heaver colder air to the outer surface and the hotter lighter air stays near the absorber where it is transferred into the water. The paper doesn't say for sure, but I would imagine that the centripetal force also pushes the water onto the inner surface of the absorber for better conduction of heat.

The paper indicates that the prototypes where about 4.5 square meters and typically produced about 1 kilowatt of steam at 100º C. That's about 1.3 horsepower. The efficiencies of the different boilers were measured and the maximum experimental efficiency with reflectors was 46%. So, based on the data in this thesis paper, it seems feasible to generate enough power to turn a very small 1 HP generator with a boiler similar to the prototypes. The steam could also be piped through a condenser and collected for water distillation and provide for several basic survival needs.

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