3-D Simulations of Charge and Mass Distribution in Tubular SOEC

Electrochemical systems that could be employed with reversible functions have been developed: electric production in a solid oxide fuel cell (SOFC) mode and hydrogen production in a solid oxide electrolysis cell (SOEC). This paper proposes a model solution using the CFD-Ace software package to simulate the behaviour of a tubular SOEC. Modelling is based on solving conservation equations of mass, momentum, energy, species and electric current by using a finite volume approach on 3D grids of arbitrary topology. The electrochemical behaviour of porous electrode is described using Butler-Volmer equations at triple phase boundaries. The 3D layouts of the current densities, electronic and ionic potentials allow to analyze respective ohmic drops. Simulations indicate that the principal damaging risks at the electrolyte/ anode interface originate from high flux densities of oxygen and from the possible re-oxidation of cermet-based cathode

Modélisation par la méthode des éléments discrets de la conductivité effective d'électrodes pour piles à combustibles à oxyde solide (SOFC)

Les électrodes composites des piles à combustible à oxyde solide (SOFC) sont obtenues par frittage partiel d'un mélange de poudres conductrices ioniques et électroniques. L'amélioration des performances électrochimiques des électrodes composites passe par la multiplication des points triples (où le gaz, le conducteur ionique et le conducteur électronique sont en contact), la présence d'une porosité résiduelle suffisante et la percolation des deux réseaux de particule (ionique et électronique). Afin d'optimiser sa microstructure, nous modélisons l'électrode poreuse comme un assemblage de sphères dont le frittage est simulé par la méthode des éléments discrets. L'empilement fritté est ensuite remplacé par un réseau de résistances électroniques, ioniques et électrochimiques et la conductivité effective est calculée. Nos simulations mettent en évidence l'importance des phénomènes de percolation. Nous calculons aussi la conductivité effective d'électrodes à gradient de composition et nous proposons une nouvelle architecture, plus performante, où la percolation du réseau électronique est forcée

Basic longitudinal texture and fracturing process in thermoset polymers

The “basic longitudinal texture”, which is present everywhere on the fracture surfaces of glassy thermosets and is the finest texture observed on such surfaces, consists of low ridges and shallow grooves that are aligned parallel with the direction of crack propagation. The periodicity of the basic longitudinal texture, i.e., the average lateral separation between the ridges (or grooves), has been found to be characteristic of materials. This and other properties were measured for a series of rigid epoxy specimens made from diglycidyl ether of bisphenol-A and methylhexahydrophthalic anhydride. For the series of epoxies studied, the glass transition temperatures varied from 76 to 143 °C, the room temperature Young's modulus varied from 2.29 to 2.97 G Pa, the room temperature yield stress in compression varied from 99 to 128 M Pa, the room temperature Knoop hardness numbers varied from 133.5 to 163.5, the rubbery modulus at 200'C varied from 12.8 to 21.6 MPa, and the periodicity of the basic longitudinal texture varied from 205 to 368 nm. Only properties of the liquid state, namely glass transition temperature and the rubbery modulus, correlated well with periodicity of the basic longitudinal texture. This suggests that the basic longitudinal texture is the remnant left on the fracture surfaces of a liquid state that must have developed during fracture. This suggests in turn that liquefaction is an intrinsic part of the brittle fracture of polymer network glasses.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44718/1/10853_2005_Article_BF01197652.pd

The high-resolution map of Oxia Planum, Mars; the landing site of the ExoMars Rosalind Franklin rover mission

This 1:30,000 scale geological map describes Oxia Planum, Mars, the landing site for the ExoMars Rosalind Franklin rover mission. The map represents our current understanding of bedrock units and their relationships prior to Rosalind Franklin’s exploration of this location. The map details 15 bedrock units organised into 6 groups and 7 textural and surficial units. The bedrock units were identified using visible and near-infrared remote sensing datasets. The objectives of this map are (i) to identify where the most astrobiologically relevant rocks are likely to be found, (ii) to show where hypotheses about their geological context (within Oxia Planum and in the wider geological history of Mars) can be tested, (iii) to inform both the long-term (hundreds of metres to ∼1 km) and the short-term (tens of metres) activity planning for rover exploration, and (iv) to allow the samples analysed by the rover to be interpreted within their regional geological context

QDB: A new database of plasma chemistries and reactions

One of the most challenging and recurring problems when modeling plasmas is the lack of data on the key atomic and molecular reactions that drive plasma processes. Even when there are data for some reactions, complete and validated datasets of chemistries are rarely available. This hinders research on plasma processes and curbs development of industrial applications. The QDB project aims to address this problem by providing a platform for provision, exchange, and validation of chemistry datasets. A new data model developed for QDB is presented. QDB collates published data on both electron scattering and heavy-particle reactions. These data are formed into reaction sets, which are then validated against experimental data where possible. This process produces both complete chemistry sets and identifies key reactions that are currently unreported in the literature. Gaps in the datasets can be filled using established theoretical methods. Initial validated chemistry sets for SF 6 /CF 4 /O 2 and SF 6 /CF 4 /N 2 /H 2 are presented as examples

Transient Analysis of Mass and Charge Transport Phenomenon of a PEMFC Gas Diffusion Electrodes

International audienc

Transient Analysis of Mass and Charge Transport Phenomenon of a PEMFC Gas Diffusion Electrodes

International audienc

Transient Analysis of Mass and Charge Transport Phenomenon of a PEMFC Gas Diffusion Electrodes

International audienc