Abstract
The favorable and adjustable transport properties of porous media make them suitable components in reactors used for solar energy conversion and storage processes. The directed engineering of the porous media’s morphology can significantly improve the performance of these reactors. We used a multiscale approach to characterize the changes in performance of exemplary solar fuel processing and solar power production reactors incorporating porous media as multifunctional components. The method applied uses imaging-based direct numerical simulations and digital image processing in combination with volume averaging theory to characterize the transport in porous media. Two samples with varying morphology (fibrous vs. foam) and varying size range (mm vs. μm scale), each with porosity between 0.46 and 0.84, were characterized. The obtained effective transport properties were used in continuum-scale models to quantify the performance of reactors incorporating multifunctional porous media for solar fuel processing by photoelectrochemical water splitting or power production by solar thermal processes.
Highlights
The direct conversion of solar energy into a storable, high-energy density fuel via solar thermochemistry or photoelectrochemistry and the solar production of power via solar thermal processes are promising renewable fuel processing and power production routes
A multiscale experimental–numerical methodology has been used to quantify the gain in performance due to engineering of the morphology of porous media used as absorber, heat exchanger, charge conductor, and reaction site in solar reactors
Two base morphologies have been investigated, i.e., fibrous and foam-like samples. Their exact morphologies were experimentally obtained via x-ray computed tomography and subsequently manipulated by digital image processing to vary characteristic morphological sizes and porosity, both at a constant base morphology
Summary
The direct conversion of solar energy into a storable, high-energy density fuel via solar thermochemistry or photoelectrochemistry and the solar production of power via solar thermal processes are promising renewable fuel processing and power production routes. The essential requirements for the processes’ impact on our fuel and power economy are their sustainable, efficient, stable, and economic implementation via solar reactors and their assembly into practical large-scale systems.[1,2,3,4] The engineering of solar reactors needs to address various issues including optimal design and operational conditions for enhanced coupled multiphysics transport and the integration and optimization of multiscale components, e.g., porous media. The latter is of special interest as porous media exhibit favorable and tunable transport properties. Interesting is the observed fourfold increase in efficiency of a solar reactor for the thermochemical splitting of water and CO2 into synthesis gas when changing the porous absorber and reactant morphology from a sintered backed bed to a highly porous foam morphology.[5,6] Similar influences on performance are expected for solar receivers used for thermal power production, which rely on porous absorber and heat exchangers of various morphologies,[7,8] or for photoelectrochemical fuel production devices relying on microstructured to nanostructured photoelectrodes[9,10,11,12,13] or separators.[14]
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