Exposed times of various metallic layers subject to a short-flash of concentrated solar energy. Theoretical-experimental evaluation

The paper outlines a methodology for the theoretical-experimental estimation of exposed times of metallic layers under the action of a short flash of concentrated solar energy. These times are of great concern when the solar thermal processing is used to make a quench of metallic slabs for modifying their hardness and stresses in a thin superficial layer. The experimental data of temperature of the disc-shaped metallic sample are obtained using the SURFSOL experimental device at SOLFACE (High Flux Solar Facilities for Europe), France. In particular, the sensors of temperature are located on its back side as the solar radiation impinges the front irradiated one. The theoretical data are obtained solving a 2D transient heat conduction problem in cylindrical coordinates using Green’s functions approach. Also, the non-linearity of the problem due to the temperature-dependent thermal properties is approached using Kirchhoff’s transformation. Comparing theoretical and experimental temperatures on the back side of the sample gives an average estimation of the solar absorption coefficient during the flash heat process. In such a way, the sample thermal field may be calculated and the temperature on its irradiated side may be derived. Finally, the surface temperature necessary for quenching a metallic slab gives the exposed time desired. It is presented in a both graphical and algebraic form for AISI 316L steel.