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- Andersson, M., et al.
(author)
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Coupling of lattice boltzmann and volume of fluid approaches to study the droplet behavior at the gas diffusion layer/gas channel interface
- 2018. - 13
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In: ECS Transactions. - : The Electrochemical Society. - 1938-6737 .- 1938-5862. - 9781607688600 ; 86, s. 329-336
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Conference paper (peer-reviewed)abstract
- A typical polymer electrolyte fuel cell (PEFC) flow field consists of micro/minichannels. The continues removal of liquid water from the cathode channels is a critical topic, as water droplets forming in the channels may block the transport of gaseous oxygen to the active sites, which not only gives an uneven current distribution and substantial loss of performance, but also, increases degradation rates and unstable operation. Water generated by the electrochemical reactions condenses, depending on temperature mainly, into liquid form, potentially flooding various part of the PEFC. The aim of this work is to obtain an increased understanding of the droplet behavior at the gas diffusion layer (GDL) interface with the gas channels in PEFCs by the coupling of Lattice Boltzmann (LB) and Volume of Fluid (VOF) approaches. A multiscale environment is established with input parameters in the VOF model being extracted from in-house LB calculations. It is clear that the contact angle as well as the size of the liquid droplet vary with positions at the GDL surface, depending on the stochastic GDL geometry. A VOF model describing one straight channel with one gas inlet, one liquid inlet (at the GDL surface) and one two-phase outlet is employed.
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- Zhang, Shidong, et al.
(author)
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Simple and complex polymer electrolyte fuel cell stack models : A comparison
- 2018. - 13
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In: ECS Transactions. - : The Electrochemical Society. - 1938-6737 .- 1938-5862. - 9781607685395 ; 86, s. 287-300
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Conference paper (peer-reviewed)abstract
- In this paper, two distinct polymer electrolyte fuel cell stack models are constructed: a detailed numerical model (DNM) employing a fine-scale computational mesh and a coarse-mesh approach based on a distributed resistance analogy (DRA) where diffusion terms in the transport equations are replaced by rate terms. Both methods are applied to a 5-cell, high-temperature polymer electrolyte fuel cell stack with an active area of 200 cm2 per cell. The polarization curve and local current density distributions from both the DRA and DNM are compared with experimental data, finding good agreement. Temperature, pressure, Nernst potential, and species distributions are also exhibited. The DNM displays details of fine-scale local extrema not captured by the DRA; however, the latter requires orders of magnitude less computer processor power and memory for execution. Both methods provide much finer-scale results than present experimental techniques.
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- Ramani-Mohan, R. -K, et al.
(author)
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Deformation strain is the main physical driver for skeletal precursors to undergo osteogenesis in earlier stages of osteogenic cell maturation
- 2018
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In: Journal of Tissue Engineering and Regenerative Medicine. - : John Wiley and Sons Ltd. - 1932-6254 .- 1932-7005. ; 12:3, s. e1474-e1479
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Journal article (peer-reviewed)abstract
- Mesenchymal stem cells play a major role during bone remodelling and are thus of high interest for tissue engineering and regenerative medicine applications. Mechanical stimuli, that is, deformation strain and interstitial fluid-flow-induced shear stress, promote osteogenic lineage commitment. However, the predominant physical stimulus that drives early osteogenic cell maturation is not clearly identified. The evaluation of each stimulus is challenging, as deformation and fluid-flow-induced shear stress interdepend. In this study, we developed a bioreactor that was used to culture mesenchymal stem cells harbouring a strain-responsive AP-1 luciferase reporter construct, on porous scaffolds. In addition to the reporter, mineralization and vitality of the cells was investigated by alizarin red staining and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide. Quantification of the expression of genes associated to bone regeneration and bone remodelling was used to confirm alizarin red measurements. Controlled perfusion and deformation of the 3-dimensional scaffold facilitated the alteration of the expression of osteogenic markers, luciferase activity, and calcification. To isolate the specific impact of scaffold deformation, a computational model was developed to derive a perfusion flow profile that results in dynamic shear stress conditions present in periodically loaded scaffolds. In comparison to actually deformed scaffolds, a lower expression of all measured readout parameters indicated that deformation strain is the predominant stimulus for skeletal precursors to undergo osteogenesis in earlier stages of osteogenic cell maturation.
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