Solar Thermal Reactor Materials Characterization Page: 4 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)
2.1 Furnace Characterization:
For the purpose of this research the power, flux profile, and heating/cooling rate measurements were the
significant variables that were tested. For the power measurements a black body absorber was placed at the
exit of the secondary. The absorber was water cooled and power was measured from the mass flow rate,
mi, and the change in temperature, AT, using the equation Q = diCpAT . The temperature of the
water at the entrance and exit of the absorber was measured using 4-wire 100-ohm platinum resistance
temperature detectors. The water flow rate was measured using a Flow Technologies FT 6-8 turbine
flowmeter with amplifier and D-A converter for analog output. Power measurements were made at varying
water flow rates to reduce calibration error from the mass flow controller. Also, the aperture opening was
varied in order to accurately predict the power during heat up and cool down and these values were
normalized for normal incident power(NIP) measurements.
Flux profile measurements were obtained using BeamView software from Coherent. A piece of frosted
quartz was placed at the exit of the secondary and a Coherent LaserCam IIID Camera was used to capture
the light intensity profile. This profile data was coupled with the power data to obtain an equation that
describes the flux at the exit of the secondary.
Soltrace was used to model the HFSF and secondary. Soltrace is a ray tracing program developed by
NREL. The program is specifically tailored to study solar systems. Solar rays coming from the sun are
discretized into individual vector elements. These vectors interact with optical elements placed on a global
coordinate system. A description of the ray-tracing procedure used is given by Spencer et al.
2.3 Thermal Cycling
Tensile testing samples of Haynes 214 were fabricated according to ASTM E8 - 04. The samples had an
overall length of .232m with a gauge thickness of .0017m and gauge length of .05m. These samples
were annealed and oxidized in a horizontal tube furnace at 1100 C for two hours to form a uniform alumina
oxide layer. A mounting rack was constructed behind the secondary concentrator and samples were
positioned .0635m behind the exit of the secondary, the same position as the reaction containing tubes in
the Dahl reactor. This configuration can be seen in Figure 3. Sample temperatures were monitored by a
pyrometer focused on the rear of the samples. The pyrometer was made by Heitronics, model KT 19.01.
Samples were slowly heated to the desired temperature and held for two minutes in order to attain a
constant temperature. To simulate cloud interference guillotine style shutters were closed and the sample
was allowed to cool. Because the thermal shock values attainable by this method are less than the AT, of
the material the samples were thermally cycled to determine material degradation. The experimental matrix
was created for three factors; maximum power level, cycle time, and number of cycles. The first two
control variables correspond to the maximum temperature, AT amplitude respectively. Maximum power
was controlled by an automatic aperture, the power levels tested were 2000 and 2500W. These power
levels correspond to approximate temperatures of 1200 and 1300 C respectively. To accommodate changes
in the NIP the aperture was looped to a control based on equations obtained from our power measurements.
Closed and opened cycle times of 20s-35s, and 40s-40s respectively, correspond to AT's of approximately
500 and 700 0C. Cycle levels were 20, 30, and 40 cycles. The experimental design was a 23 factorial with a
center point in the cycle factor to determine curvature. Each point of this factorial design was performed
twice and the order was randomized.
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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/m1/4/: accessed December 16, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.