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Improvement of radiative performances of high temperature solar particle receivers using coated particles and mixtures

Abstract:

The use of HfB2, ZrB2, HfC, ZrC, W, and SiC particles in a high temperature solar particle receiver (SPR) is analyzed. The SPR is modeled as a 1D slab of spherical particles dispersion, submitted to a concentrated and collimated solar flux (q0 €‰= €‰1500 €‰kW/m2). The temperature inside the SPR is taken constant (T €‰= €‰1300 €‰K), as for a well-stirred receiver. For the W and SiC, the refractive indexes reported in the literature are retained while the real and imaginary parts of the refractive indexes of the others materials are obtained from available reflectance data, using the Kramers-Kronig (KK) relationships. Three SPR configurations are considered: a homogeneous medium with only one kind of particles, a medium with a mixture of two materials and a medium with coated particles. The three configuration results are compared with those obtained using particles made with an ideal material. For the first configuration, the lowest radiative losses are found using small particles of sizes close to d €‰= €‰2 €‰ 1/4m. For the second configuration, non-noticeable improvements are found by the use of mixtures of the studied materials. For the third configuration, when the SiC is used as mantle, the radiative losses decrease to approach the ideal minimum. The best combination corresponds to a particle with a core of W coated by SiC. Improvements of 2.6% and 2.8% may be achieved using coating thickness of 50 €‰nm with particles of d €‰= €‰2 €‰ 1/4m and d €‰= €‰100 €‰ 1/4m, respectively. The use of coated particles may thus lead to significant improvements in the radiative performances of a SPR working at high temperature.