Solar Thermal Reactor Materials Characterization Page: 2 of 8
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2008 14th Biennial CSP SolarPACES (Solar Power and Chemical Energy Systems) Symposium, 4-7 March 2008, Las Vegas, Nevada (CD-ROM) (NREL/CD-550-42709)
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Figure 1. Solar thermal aerosol reactor (a) schematic, (b) installed used by Dahl et. al.
Because the methane dissociation reaction did not involve any oxygen graphite tubes were used because of
their superior high temperature and thermal shock stability. Due to the creation of oxygen during the
dissociation step of metal oxide reactions (e.g. ZnO, Mn2O3, Fe304), tube materials must be oxidation
resistant. Several candidate materials, such as Alumina and Silicon Carbide, have undergone preliminary
testing at the HFSF. The unpublished results of these tests showed that samples subjected to the intense
solar radiation cycling exhibited lifetimes much shorter than expected. The primary failure mechanism was
radial fracture. It is believed that this failure is due in part to the large temperature gradient across the tube
surface. This gradient is a function of the slow heat conduction within the materials and the unique thermal
profile created by the incident solar energy. The motivation of this research is to couple the solar
characteristics of the HFSF with the stresses induced in the test materials to more easily select usable solar
1.2 Concentrated Solar Energy:
Concentrated solar energy focuses large areas of sunlight onto a very small point using concave mirrors or
lenses. Peak concentrations at the HFSF using a secondary concentrator reach 2500 W/m^2, with maximum
theoretical power up to 10 kW. This type of solar application produces unique flux profiles that create
drastic thermal gradients within sample materials. Lewandowski et. al originally characterized the HFSF by
measuring the power profile using seven horizontal 2.5cm diameter calorimeters. The flux intensity was
measured as a function of position along the focal axis. These test were performed for the beam produced
by the primary concentrator and then again for a round compound parabolic concentrator. In addition flux
profiles were measured using BEAMCODE analysis software. A similar approach has been attempted to
characterize the HFSF with the octagonal secondary concentrator used by Dahl et. al. for the solar thermal
The secondary is composed of eight mirrors attached at compound angles to produce a cone with a
rectangular exit. The mirrored surface was achieved by coating the internal face of the pieces with
protected silver. Recent measurements of the reflectance of the secondary show an average reflectance of
96 percent. A picture of the secondary assembly can be seen in Figure 2. The flux profile of the incident
solar radiation at the exit of the secondary is pertinent to accurately modeling the conditions seen by the
reaction containing tube.
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Lichty, P. R.; Scott, A. M.; Perkins, C. M.; Bingham, C. & Weimer, A. W. Solar Thermal Reactor Materials Characterization, article, March 1, 2008; Golden, Colorado. (digital.library.unt.edu/ark:/67531/metadc901904/m1/2/: accessed September 21, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.