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45. Computational study of heat and mass transfer issues in solid oxide fuel cells

Author

Beale, Steven B., Roth, Helmut K., Choi, Hae-Won, Jeon, Dong Hyup, and Pharaoh, Jon G.

Subjects
Physics::Fluid Dynamics, Cross-flow, Co-flow, Temperature uniformity, Numerical modelling, OpenFOAM, Solid oxide fuel cells, Counter-flow
Abstract

Temperature uniformity contributes to minimizing material stress and improving lifetime in solid oxide fuel cells. This paper investigates the temperature distribution in three flow field configurations: co-flow, counter-flow and cross-flow. A three-dimensional computational fluid dynamics model coupling transport and electrochemistry is developed within the framework of an existing open source library. Porous electrodes with effetive diffusivities and interconnect rib geometries are accounted for. Two different approaches were investigated ain obtaining effective diffusion coefficients for the porous transport layers. A lumped internal resistance model is implemented for the calculation of electrochemical reaction and Joule heating. The temperature profiles are influenced by the fluid (either air or fuel) flow passage and the interconnect rib geometry. Among the three geometry configurations considered, the counter-flow case produces the most uniform temperature distribution with the smallest temperature variation.

Published
2015

49. Synthesis of a Ca3SiO5–Ca2SiO4–Ca3Al2O6 cement system with rapid setting capacity by spray‐pyrolysis coupled with sol–gel method.

Author

Choi, Hae Won, Um, Seung‐Hoon, and Rhee, Sang‐Hoon

Subjects
ALUMINUM oxide, SOL-gel processes, PYROLYSIS, CHEMICAL reactions, METAL powders
Abstract

A modified mineral‐trioxide‐aggregate (mMTA) with rapid setting capacity was newly synthesized by spray‐pyrolysis following a sol–gel reaction. Its faster setting capacity and initially higher compressive strength compared with Portland cement (PC) were evaluated. The precursor solution of the mMTA was prepared through condensation following hydrolysis among Ca(NO3)2·4H2O, Si(OC2H5)4, and Al(NO3)3·9H2O under nitric acid. The mMTA powder was then synthesized by spray‐pyrolysis at 1500°C. The particle shape was spherical with an average particle size of 0.8 ± 0.3 μm, while PC particles were irregular and 3.9 ± 3.0 μm in size. The mMTA consisted of mostly Ca3SiO5, Ca3Al2O6, and partial Ca2SiO4 phases, while the PC comprised mainly Ca3SiO5, Ca2SiO4, and partial Ca3Al2O6 phases. The final setting times of mMTA and PC measured under 95% relative humidity were about 11 min and 3 h, respectively. The early stage of setting in mMTA was dominated by the rapid formation of hexagonal‐plate‐like Ca3Al2O6·6H2O crystals, while that in PC was dominated by needle‐like calcium‐silicate‐hydrate gels and columnar‐shaped Ca(OH)2 crystals. The late stage of setting in mMTA was dominated by calcium‐silicate‐hydrate gels and Ca(OH)2 crystals, while that in PC was dominated by Ca3Al2O6·6H2O crystals. The compressive strengths of mMTA and PC after 30 min of setting were 4.5 and 0.2 MPa, respectively. The results suggest that mMTA has potential to be used as a filling material for accidental pulp‐exposure or pulpal floor perforation cases that require rapid setting capacity and initial good strength. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 1440–1451, 2019. [ABSTRACT FROM AUTHOR]

Published
2019
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