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Second Thermal and Fluids Engineering  Conference

ISSN: 2379-1748
ISBN: 978-1-56700-430-4

Transient heat transfer analysis in a fluidized bed of metal oxide particles undergoing solar thermochemical reduction




Abstract

Two-step metal oxide redox cycles are a promising route to efficiently store solar energy chemically. In the first process step, a metal oxide is reduced in a reducing atmosphere above 1000°C. In the second process step, the metal oxide is re-oxidized either with gaseous oxygen to generate high-temperature heat for solar power production, or with H2O and CO2 to produce syngas for solar fuel production. Fluidized-bed reactors are considered to conduct the thermal reduction step. They offer high heat and mass transfer rates via radiative heat transfer and turbulent mixing, and reduce the risk of particle aggregation and sintering. In this numerical study, we investigate the transient heat and mass transfer in a directly-irradiated plane-parallel medium containing a suspension of ceria (cerium dioxide) particles undergoing non-stoichiometric thermal reduction. The micrometer-sized particles are assumed to be homogenous, non-gray, absorbing, emitting, and anisotropically scattering, while the overall medium is of non-uniform temperature and composition. The unsteady mass and energy conservation equations are solved using the finite-volume method and the explicit Euler time-integration scheme. Radiative transport is modeled using the energy-partitioning Monte Carlo ray-tracing method. The radiative properties are obtained using the Mie theory. Convective heat transfer between particles and the fluidizing nitrogen gas flow is calculated for the case of small particles (1−20 micrometer diameter), low particle volume fractions and low particle Reynolds numbers. A parametric study is performed to study the influence of selected model parameters.

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