Heat transfer simulation in a thermochemical solar reactor based on a volumetric porous receiver

A 1 kW thermochemical solar reactor/receiver fitted with a porous ceramic foam structure is studied numerically to predict the thermal transfers inside the volumetric solar receiver. This reactor is devoted to the production of hydrogen from two-step thermochemical cycles based on mixed metal oxides, and it features a porous media coated with the reactive ferrite material (MxFe3−xO4) that is directly irradiated by concentrated solar energy. The developed numerical model couples the fluid flow, heat and mass transfer, and the chemical reactions. The FLUENT code solves the transport equations of the fluid phase. The source terms of the solid phase, radiative heat transfer and chemical reactions are then computed using user-defined functions. The complete model was used to predict the thermal behavior of the receiver under different operational conditions, which concerns the inert gas flow rate, the incident solar flux, the porosity, the mean cell size of the foam, the length of the volumetric solar receiver, and the influence of the chemical reactions. Results show that the maximal temperature of the foam is around 1710 K with 6 Ln/min N2 for a mean solar concentration of 1040 suns. The higher the gas flow rate, the lower the temperature of the foam. The suitable operating conditions were defined for carrying out the reduction and hydrolysis reactions in the whole reactor volume at 1400 K and 1200 K, respectively. A model validation was performed with experimental data obtained from the reactor testing at the focus of a solar furnace.