P 820 – Processing of solar absorbers in steel design based on partially roll bonded hybrid semifinished parts
In this project a full plane streamed demonstrator solar absorber was developed, which has a bionic channel design (FracTherm®). The composition of the absorber is module based, so that this concept gives the possibility for flexible collector sizes and with that an additional architectonic benefit.
Hence, a process chain, consisting of partial cold roll bonding and subsequent inner hydroforming, was used for production. In the process two sheet metal strips are roll bonded to a cladded semi-finished part. Taking into account the elongation as a result of the rolling process, a release agent is applied onto the strip, which prevents he bonding of the sheets along the later emerging channel structure. The so produced semi-finished part consists, on the upper side, of a threelayered material compound (copper-steelcopper) and, on the lower side, of steel. For a pure steel-steelcompound significant cost advantages exist. For the subsequent forming with inner high pressure, a special sealing concept is mandatory. Here, this problem was solved with a conical docking device combined with an elastomer sealing. A welding of the connection points is not possible due to the mating materials steel and copper. The forming of the semi-finished parts was carried out by a forming tool in a high pressure sheet metal forming press with a locking force of 22.5 MN and a working media pressure of 65 MPa.
The measurement of the water flow of the new demonstrator absorber by means of thermography measurement shows a good distribution. The pressure drop is comparatively small. The collector efficiency factor F’, a fundamental parameter of the thermic efficiency, is in face of the less heat conductivity through a suitable channel design very high. Therefore, for FracTherm® absorbers, a high collector efficiency factor F’ is expected.
Up to now steel is only less used in solar absorbers. With the here shown novel process chain, the use of steel can be increased. In combination with the bionic channel design further advantages are resulted. By the module-based concept more not yet seen possibilities for embedding the solar heat power in the architecture are arising as before.
The research project (IGF-Nr. 339 ZN) was carried out at Technical University Dortmund, Institut für Umformtechnik und Leichtbau and at Fraunhofer-Institut für Solare Energiesysteme, Freiburg. FOSTA has accompanied the research project work and has organized the project funding from the Federal Ministry of Economics and Technology through the AiF as part of the programme for promoting industrial cooperation research (IGF) in accordance with a resolution of the German parliament.
Only availlable in german language.
A. E. Tekkaya, F. Steinbach, L. Koch, M. Hermann