Performance investigation on solar thermal conversion of a conical cavity receiver employing a beam-down solar tower concentrator

Development of a beam-down solar tower (BST) with strong wind-resistance heliostats is a particular topic of active research. A BST system, equipped with three linear Fresnel heliostat modules, corresponding beam-down concentrators, and a central cavity receiver with a spiral tube, has been introduced, experimentally investigated and theoretically analyzed in this paper. The elaborate derivation process of sun-tracking formulas for the BST collector has been implemented. In addition, detailed numerical models for thermal behaviors of the conical cavity receiver with the spiral tube, on the basis of three-dimensional Computing Finite Dynamics (CFD) method, have been developed and validated with experimental data. The objective of this paper is to report test results of the conical receiver equipped the BST concentrator, and to numerically evaluate conversion performance of the solar thermal process including the heat flux distribution on the absorber surface, heat losses, as well as instantaneous thermal efficiencies, thereby providing useful data for the optimization of the cavity receiver. Experimental results and numerical prediction indicate that instantaneous thermal efficiencies of about 60% and 39% can be reached at differences of 81 K and 181 K between inlet and ambient temperatures under water and Therminol VP-1 flow rates of 0.5 l/s, respectively. The operational volume flow rates of 0.25 l/s and 0.35 l/s are respectively suggested to the conical cavity receiver using water and Therminol VP-1 under the geometry and operational conditions in this paper. The optimal conical angle of 100° has a minimum heat loss leading to obtain a maximum thermal efficiency.