Parametric Analysis of a High Temperature Sensible Heat Storage System by Numerical Simulations

This work has been realized in the framework of the Elioslab project, financed by the Italian Ministry of Education, University and Research (MIUR), which aims to create a research platform in order to develop components and systems for the production and utilization of medium and high temperature heat using concentrated solar energy. As regards high temperature heat production, a 30 kW solar furnace that consists of a heliostat with flat mirrors and a parabolic concentrator with off-axis alignment is being realized in order to achieve a solar radiation concentration peak of about 2000 suns. The energy flux relative to the concentrated radiation will be converted to high temperature heat by a cavity receiver cooled with CO₂, and finally transferred to a device operating at high temperature consisting in a thermochemical reactor for hydrogen production. Due to the intermittency of solar radiation, a high temperature (>800 °C) packed bed sensible heat storage system, with alumina balls as heat storage material, has been developed in order to provide continuity to the user operation. This paper focuses on the parametric analysis that has been carried out by means of numerical simulations to evaluate the set of variable parameters that maximize the efficiency of the heat storage system of the solar furnace. The charging and discharging phases of the heat storage tank have been numerically simulated by means of an analytical model that takes into account the conductive, convective, and radiative heat transfer as well as turbulent diffusion due to the solid–fluid interaction. The results of the numerical parametric analysis are presented together with the experimental validation of the adopted analytical model accomplished by using a reduced-scale high temperature storage system.