Biomimetic flow fields for proton exchange membrane fuel cells: A review of design trends

Bipolar Plate design is one of the most active research fields in Polymer Electrolyte Membrane Fuel Cells (PEMFCs) development. Bipolar Plates are key components for ensuring an appropriate water management within the cell, preventing flooding and enhancing the cell operation at high current densities. This work presents a literature review covering bipolar plate designs based on nature or biological structures such as fractals, leaves or lungs. Biological inspiration comes from the fact that fluid distribution systems found in plants and animals such as leaves, blood vessels, or lungs perform their functions (mostly the same functions that are required for bipolar plates) with a remarkable efficiency, after millions of years of natural evolution. Such biomimetic designs have been explored to date with success, but it is generally acknowledged that biomimetic designs have not yet achieved their full potential. Many biomimetic designs have been derived using computer simulation tools, in particular Computational Fluid Dynamics (CFD) so that the use of CFD is included in the review. A detailed review including performance benchmarking, time line evolution, challenges and proposals, as well as manufacturing issues is discussed.Ministerio de Ciencia, Innovación y Universidades ENE2017-91159-EXPMinisterio de Economía y Competitividad UNSE15-CE296

Model-based analysis for the thermal management of open-cathode proton exchange membrane fuel cell systems concerning efficiency and stability

In this work we present a dynamic, control-oriented, concentrated parameter model of an open-cathode proton exchange membrane fuel cell system for the study of stability and efficiency improvement with respect to thermal management. The system model consists of two dynamic states which are the fuel cell temperature and the liquid water saturation in the cathode catalyst layer. The control action of the system is the inlet air velocity of the cathode air flow manifold, set by the cooling fan, and the system output is the stack voltage. From the model we derive the equilibrium points and eigenvalues within a set of operating conditions and subsequently discuss stability and the possibility of efficiency improvement. The model confirms the existence of a temperature-dependent maximum power in the moderate temperature region. The stability analysis shows that the maximum power line decomposes the phase plane in two parts, namely stable and unstable equilibrium points. The model is capable of predicting the temperature of a stable steady-state voltage maximum and the simulation results serve for the design of optimal thermal management strategies.Postprint (author's final draft

On the small-scale stability of thermonuclear flames in Type Ia supernovae

We present a numerical model which allows us to investigate thermonuclear flames in Type Ia supernova explosions. The model is based on a finite-volume explicit hydrodynamics solver employing PPM. Using the level-set technique combined with in-cell reconstruction and flux-splitting schemes we are able to describe the flame in the discontinuity approximation. We apply our implementation to flame propagation in Chandrasekhar-mass Type Ia supernova models. In particular we concentrate on intermediate scales between the flame width and the Gibson-scale, where the burning front is subject to the Landau-Darrieus instability. We are able to reproduce the theoretical prediction on the growth rates of perturbations in the linear regime and observe the stabilization of the flame in a cellular shape. The increase of the mean burning velocity due to the enlarged flame surface is measured. Results of our simulation are in agreement with semianalytical studies.Comment: 9 pages, 7 figures, Uses AASTEX, emulateapj5.sty, onecolfloat.sty. Replaced with accepted version (ApJ), Figures 1 and 3 are ne

Marine aerobic biofilm as biocathode catalyst

Stainless steel electrodes were immersed in open seawater and polarized for some days at − 200 mV vs. Ag/AgCl. The current increase indicated the formation of biofilms that catalysed the electrochemical reduction of oxygen. These wild, electrochemically active (EA) biofilms were scraped, resuspended in seawater and used as the inoculum in closed 0.5 L electrochemical reactors. This procedure allowed marine biofilms that are able to catalyse oxygen reduction to be formed in small, closed small vessels for the first time. Potential polarisation during biofilm formation was required to obtain EA biofilms and the roughness of the surface favoured high current values. The low availability of nutrients was shown to be a main limitation. Using an open reactor continuously fed with filtered seawater multiplied the current density by a factor of around 20, up to 60 µA/cm2, which was higher than the current density provided in open seawater by the initial wild biofilm. These high values were attributed to continuous feeding with the nutrients contained in seawater and to suppression of the indigenous microbial species that compete with EA strains in natural open environments. Pure isolates were extracted from the wild biofilms and checked for EA properties. Of more than thirty different species tested, only Winogradskyella poriferorum and Acinetobacter johsonii gave current densities of respectively 7% and 3% of the current obtained with the wild biofilm used as inoculum. Current densities obtained with pure cultures were lower than those obtained with wild biofilms. It is suspected that synergetic effects occur in whole biofilms or/and that wild strains may be more efficient than the cultured isolates

An Evolutionary Economic Analysis of Energy Transitions

Evolutionary economics offers clear insights into the mechanisms that underlie innovations, structural change and transitions. It is therefore of great value for the framing of policies aimed at fostering a transition to a sustainable development. This paper offers an overview of the main insights of evolutionary economics and derives core concepts, namely ‘diversity’, ‘innovation’, ‘selection environment’, ‘bounded rationality’, ‘path dependence and lock-in’, and ‘coevolution’. These concepts are subsequently used to formulate guidelines for the role of the government and the design of public policies, such as the learning from historical technological pathways and the creation of an extended level playing field. In addition, the developments of certain energy technologies are examined in detail within the adopted evolutionary economics framework. Three particular technologies received attention, namely fuel cells, nuclear fusion, and photovoltaic cells.

Chemistry: Space resources for teachers including suggestions for classroom activities and laboratory experiments

Curriculum supplement to assist general chemistry teachers in updating instruction materials with aerospace development