(297c) Transient Heat and Mass Transfer Analysis of a Porous Reactive Ceria Structure for Solar Fuel Production Via Thermochemical Redox Cycling

A high-temperature isothermal solar thermochemical reactor has been proposed for production of synthesis gas from CO₂ and H₂O using ceria-based redox cycles. The reactor cavity is an assembly of annular reactive elements made of highly porous ceria with embedded inlet and outlet gas channels. Simultaneous reduction and oxidation takes place in separate reactive elements. The reactor cavity is subjected to an incident concentrated solar flux of 3000 suns at the aperture. The coupled transport processes of heat and mass transfer along with gas-solid chemical reactions have been numerically modeled in the present study. The developed model is transient, three-dimensional and for a single reactive element undergoing partial reduction when argon gas sweeps through the reactive material. The extended Darcy−Brinkman−Forchheimer formulation is used to model fluid flow through the porous region. For the free fluid domain in the gas channels step-changes are implemented to the values of permeability and porosity allowing the use of a unified momentum transport equation throughout the problem domain. Local thermal non-equilibrium is expected and energy equations are solved in both phases of the porous medium to obtain the respective temperature fields. Rosseland diffusion approximation is employed to compute the internal radiative transport in the solid phase. The incident heat flux on the reactive element is determined by iteratively calculating the net radiative heat exchange inside the cavity. The model is applied to determine influence of geometric design parameters, operating conditions and morphological parameters on the average reaction rate, outlet gas composition and average pressure drop that are treated as indicators of performance of the reactive element. The effect of variations in the thickness of the reactive element, number of elements in the reactor and sweep gas flow rates have been analyzed to optimize the design of the reactive element.