Thermochemical Solar Reactor: Simplified Method for the Geometrical Optimization at a Given Incident Flux

Abstract

This paper aims to describe a simplified method to optimize the geometry of a solar thermochemical reactor. As a first step, this paper focuses on a purely thermal analysis. The chemical reaction is represented by a uniform heat sink inside the material. The heat transfer modes are radiation in the empty part (cavity) and conduction inside the reactive material. The aim is to find the optimal geometry of the reactor, by maximizing its efficiency, for a fixed value of the incident solar flux and of the total volume of the reactor. An analytical solution can be found thanks to some simplifying hypothesis. The influence of different operational parameters on the maximal efficiency and on the optimal shape is studied. A comparison between different reactor designs (cylindrical and cavity reactors) is shown. A 2D study, based on CFD software using a finite element method, allows for quantifying the effects of the simplifying assumptions. The constructal theory aims to optimize the internal structure of a system in order to provide easier access to its internal currents and increase the system efficiency. Thus, this study can be seen as the optimization of the elemental volume of the constructal approach. In a next step this optimization method will be used to optimize more complex reactor design, as for example, a honeycomb reactor obtained by the assembling of several cavities, in order to optimize a thermochemical reactor for hydrogen production or high temperature heat storage.