Processing of new solar absorbers in steel design based on partially cold roll bonded hybrid semi-finished parts

A new approach of manufacturing solar absorbers is presented with which it is possible to design the channel geometry as a quasi-fractal structure. The so called FracThermR structure (developed by Fraunhofer Institute for Solar Energy Systems) aims at reducing the pressure drop and at a uniform flow distribution. To manufacture these new absorbers, a fast, nearly continuous production process was developed which consists of partial cold roll bonding and subsequent hydroforming, similar to symmetric hydroforming of sheet metal pairs. With the help of a small demonstrator the feasibility of the hydroforming process is shown and the process chain is validated.