Pore-level engineering of macroporous media for increased performance of solar-driven thermochemical fuel processing

Abstract

a b s t r a c tThe performance of high-temperature solar reactors incorporating porous ceramic materials that serve as radiative absorbers and chemical reaction sites can be improved significantly by tailoring their pore structure. We investigated the changes in their effective heat and mass transport properties with increasing mass loading of porous ceramics fabricated by the replica method. We applied a methodology consisting of the experimental characterization of the structure via 3D tomographic techniques coupled to pore-level direct numerical simulations for the determination of the effective transport properties. This approach was extended by using digital image processing on the structure data to allow for artificial changes in the morphological characteristics -corresponding to actual variations in the fabrication process. We derived transport correlations of porous ceria foam with varying mass loading, i.e. reticulate to dense foams with porosity from 0.85 to 0.45. We observed that the correlations proposed in literature do not accurately describe the behavior of low-porosity foams. The numerical findings of this study provide guidance for pore-level engineering of materials used in solar reactors and other high-temperature heat and mass transfer applications.

Modelling of solar thermochemical reaction systems

“…Dense fluidised reactor Stationary reactor Material study CeO 2 (Oles and Jackson, 2015) (Groehn et al, 2016) (Bader et al, 2015;Bala Chandran et al, 2015b) (Bala Chandran et al, 2015aKeene et al, 2013Keene et al, , 2014Lapp et al, 2013;Lapp and Lipiń ski, 2014) t (Wheeler et al, 2014) (Suter et al, 2014) (Dombrovsky et al, 2012;Ganesan et al, 2013a,b) * , , (Ackermann et al, 2014(Ackermann et al, , 2017 ZnO/Zn Geometry only (Akolkar and Petrasch, 2012;Jörg Petrasch, Meier, et al, 2008;Petrasch et al, 2007) Other (Lu et al, 2016) …”

“…ð10Þ a correction necessary when the Reynolds number is greater than unity (Suter et al, 2014). Here K is the permeability tensor of the porous material and F is the D-F coefficient.…”

“…REVs can be determined by calculating morphological and transport properties in sub-volumes of the sample with increasing size until the results converge to a nearly constant value. REVs are generally determined based on morphological characteristics, such as porosity (Petrasch et al, 2008a,b,c), or specific volume (Suter et al, 2014). They are typically described by cubical volumes with edge lengths somewhere between 5 and 10 times the characteristics structural dimension of the sample (for example nominal pore diameter, or mean particle diameter).…”

“…In such a case, a statistical approach needs to be followed; multiple computed tomography datasets of different regions of the physical sample need to be obtained and used to determine the transport property as a statistical average obtained for the various sub-REV samples. Beyond characterising, authors have attempted to find optimised pore structures for STRS applications Petrasch, 2011, 2012;Suter et al, 2014;Suter and Haussener, 2013;. The latest work in this line of research is a superset of previous works where the permeability, D-F coefficient, effective thermal conductivity, volumetric heat transfer coefficient, and effective extinction coefficient for porous ceria are found for reticulate porous ceria with changing porosity (Suter et al, 2014), and then applied in a simple 1D case to show the impact of morphology on the performance (Suter and Haussener, 2013).…”

“…Beyond characterising, authors have attempted to find optimised pore structures for STRS applications Petrasch, 2011, 2012;Suter et al, 2014;Suter and Haussener, 2013;. The latest work in this line of research is a superset of previous works where the permeability, D-F coefficient, effective thermal conductivity, volumetric heat transfer coefficient, and effective extinction coefficient for porous ceria are found for reticulate porous ceria with changing porosity (Suter et al, 2014), and then applied in a simple 1D case to show the impact of morphology on the performance (Suter and Haussener, 2013). Suter et al (2014) investigated reticulate porous ceramic samples with porosities within a range of 0.45-0.85, all for the same base morphology.…”