Effective Heat and Mass Transport Properties of Anisotropic Porous Ceria for Solar Thermochemical Fuel Generation

Xiang

Spurgeon

et al. 2012

Energy Environ. Sci.

Self Cite

281

394

A validated multi-physics numerical model that accounts for charge and species conservation, fluid flow, and electrochemical processes has been used to analyze the performance of solar-driven photoelectrochemical water-splitting systems. The modeling has provided an in-depth analysis of conceptual designs, proof-of-concepts, feasibility investigations, and quantification of performance. The modeling has led to the formulation of design guidelines at the system and component levels, and has identified quantifiable gaps that warrant further research effort at the component level. The two characteristic generic types of photoelectrochemical systems that were analyzed utilized: (i) side-by-side photoelectrodes and (ii) back-to-back photoelectrodes. In these designs, small electrode dimensions (mm to cm range) and large electrolyte heights were required to produce small overall resistive losses in the system. Additionally, thick, non-permeable separators were required to achieve acceptably low rates of product crossover.

Section: Diffusive and Convective Crossovermentioning

confidence: 99%

Modeling, simulation, and design criteria for photoelectrochemical water-splitting systems

Xiang

Spurgeon

et al. 2012

Energy Environ. Sci.

Self Cite

281

394

“…The porosity ranges between 0.85 and 0.38 for the ds and ws snow types, respectively, and the characteristic mean ice particle diameter ranges between 50 and 660 μm for the ds and ws snow types, respectively [14] . These morphological characteristics (summarized in Table 1 ) have been previously calculated based on two-point correlation functions (porosity and specific surface), mathematical opening operations (size distributions), and porosity calculations of increasing subvolumes (representative volume) [13] . The soot agglomerates are approximated by a collection of monodisperse, spherical particles with a primary particle diameter size, d p , and composed of a certain number of particles, N p .…”

Section: Agglomerate and Snow Morphologiesmentioning

confidence: 99%

“…The fractal dimension ranged between 2.35-2.17 and 2.03-2.08 for the compact and the chain-like agglomerates, respectively, and the anisotropy ranged between 0.186-0.202 and 0.310-0.302 for compact and chain-like agglomerates, respectively ( Table 2 ). The anisotropy was quantified based on a mean intercept length calculation [13] , where anisotropies close to 0 represent isotropic media and anisotropies close to 1 strongly anisotropic media. The experimentally determined fractal dimension of soot particles spans a range between 2.1 (for flame-generated soot particles) and 2.3 (for diesel exhaust particle matter) [42] .…”

Section: Agglomerate and Snow Morphologiesmentioning

confidence: 99%

Optical characterization of multi-scale morphologically complex heterogeneous media – Application to snow with soot impurities

Dai

Journal of Quantitative Spectroscopy and Radiative Transfer

2018

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a b s t r a c tA multi-scale methodology for the radiative transfer analysis of heterogeneous media composed of morphologically-complex components on two distinct scales is presented. The methodology incorporates the exact morphology at the various scales and utilizes volume-averaging approaches with the corresponding effective properties to couple the scales. At the continuum level, the volume-averaged coupled radiative transfer equations are solved utilizing ( i ) effective radiative transport properties obtained by direct Monte Carlo simulations at the pore level, and ( ii ) averaged bulk material properties obtained at particle level by Lorenz-Mie theory or discrete dipole approximation calculations. This model is applied to a soot-contaminated snow layer, and is experimentally validated with reflectance measurements of such layers. A quantitative and decoupled understanding of the morphological effect on the radiative transport is achieved, and a significant influence of the dual-scale morphology on the macroscopic optical behavior is observed. Our results show that with a small amount of soot particles, of the order of 1ppb in volume fraction, the reduction in reflectance of a snow layer with large ice grains can reach up to 77% (at a wavelength of 0.3 μm). Soot impurities modeled as compact agglomerates yield 2-3% lower reduction of the reflectance in a thick show layer compared to snow with soot impurities modeled as chain-like agglomerates. Soot impurities modeled as equivalent spherical particles underestimate the reflectance reduction by 2-8%. This study implies that the morphology of the heterogeneities in a media significantly affects the macroscopic optical behavior and, specifically for the soot-contaminated snow, indicates the non-negligible role of soot on the absorption behavior of snow layers. It can be equally used in technical applications for the assessment and optimization of optical performance in multi-scale media.

“…[36][37][38][52][53][54][55][56][57][58][59], and is omitted from this article for brevity. CT-based DPLS was applied, among others, to determine the effective transport properties of a Rh-coated SiC RPC used for the solar reforming of CH 4 [56][57][58][59], of a packed bed of semitransparent CaCO 3 particles used for the solar production of lime and cement [36], of an RPC used for the solar thermal dissociation of H 2 SO 4 [60], of a reacting packed bed of carbonaceous materials undergoing gasification [61,62], and of an anisotropic ceria monolith used for the splitting of H 2 O and CO 2 via redox cycles [63].…”

Section: Tomography-based Characterization Of Solar Reacting Mediamentioning

confidence: 99%

Review of Heat Transfer Research for Solar Thermochemical Applications

Lipiński¹,

Davidson

Journal of Thermal Science and Engineering Applications

et al. 2013

This article reviews the progress, challenges and opportunities in heat transfer research as applied to high-temperature thermochemical systems that use high-flux solar irradiation as the source of process heat. Selected pertinent areas such as radiative spectroscopy and tomography-based heat and mass characterization of heterogeneous media, kinetics of high-temperature heterogeneous reactions, heat and mass transfer modeling of solar thermochemical systems, and thermal measurements in high-temperature systems are presented, with brief discussions of their methods and example results from selected applications.