(599b) Materials Characterization for High Temperature Solar Hydrogen Production
Concentrated solar energy focuses large amounts of sunlight onto a small area producing high temperatures (~2000°C). A novel multi-tube solar thermal aerosol reactor has been designed for testing at the High Flux Solar Furnace(HFSF) at the National Renewable Energy Laboratory(NREL) in Golden, Colorado. The reactor consists of a reflective outer cavity which houses several absorbing, reaction containing tubes. Concentrated solar energy impinges upon the absorbing tubes through a window in the outer chamber. Ray trace modeling of the HFSF coupled with experimental characterization has provided power and flux profile boundary conditions entering the chamber. Usable reactor materials must be capable of withstanding high temperature corrosive environments and rapid temperature variations. Rapid changes in temperatures cause internal material stresses. An investigation of the typical stresses produced through high temperature thermal cycling at the HFSF provides criteria for selecting functional materials. Candidate materials are subjected to thermal cycling. Tensile stress samples undergo rapid heating and cooling at the HFSF. Residual strength is measured through tensile testing of the cycled samples. Stress estimations as well as lifetime estimates are analyzed from the residual strength data. These tests coupled with computational thermal stress analysis will provide a stress history specific to the flux profile produced by the HFSF. Localized stress intensity factors will be calculated from modeling and compared to experimental results. Stress intensity factors will be quantified locally by subjecting large planar samples with multiple, distributed, vicker's indentations to the HFSF flux profile. Analysis of crack propagation as a function of indentation location and number of cycles will provide validation of modeled stress intensity. Preliminary results from these tests will be presented as well as comparison to computational model.