Bruno Auvity

Global energy optimization of a light-duty fuel-cell vehicle

In this paper, an analytic tank to wheel model of a light-duty fuel-cell vehicle is presented. This model takes into account all the elements of the vehicle along with their interactions. It is used to optimize the velocity profile of the vehicle in order to minimize the energy consumption per kilometer.

Multiphysics Modeling and Driving Strategy Optimization of an Urban-Concept Vehicle

This paper is dedicated to the optimization of the driving strategy of a high efficiency fuel cell based power train. This power train is developed to equip an urban-concept vehicle that runs energetic races where the objectives are to go the furthest with the lowest quantity of fuel (Shell Eco Marathon). Through a comprehensive dynamical model, including the mechanical requirement, the thermal behavior of the fuel cell stack and the various losses and consumption of the power train devices. This model is then integrated into a global optimization algorithm, to determine the best race strategy to be adopted (velocity profile, motor current, gearbox ratio).

Change of Preferential Liquid Breakthrough Pathways in PEMFC Gas Diffusion Layers: Evidence of Pressure-Induced Dynamic Transport

In this work, the change of liquid water preferential pathways through PEM fuel cell Gas Diffusion Layers (GDL) with ex situ devices is investigated. A capillary network constituted of two connected micro channels is first developed. It is shown that once the larger channel has been invaded, the pressure variation due to the growth of the water droplets at the channel tip enables the liquid water to invade the smaller capillary channel. At the end, the liquid preferential path is modified. This result is then generalized considering a real GDL. Liquid water is injected through the GDL to a micro channel, and changes in liquid water pathways are observed after several hours of operations. The reported experimental observations show that pressure-induced dynamic transport due the water droplet eruption in the channel has to be taken into account to predict the preferential pathway after long time of fuel cell operation.

Fluid dynamic breakthrough in two connected capillaries: From stationary to oscillating state

In this paper, we investigate the pore structure and the impacts of Haines jumps on the change in preferential pathways (called the dynamic breakthrough) during fluid percolation through thin porous media. Two capillaries connected in parallel are used to represent a thin porous medium, and Haines jumps are observed through the formation of droplets. Using a droplet growth model and experimental visualisations, the change in preferential pathways is shown to be strongly influenced by the pore lengths, pore radii ratios, and droplet detachment volumes. This work provides a better understanding of the redevelopment of continuous fluid paths observed through thin porous media in electrochemical systems.

Transient Fluid Forces on a Rigid Circular Cylinder Subjected to Small Amplitude Motions

The present paper treats the transient fluid forces experienced by a rigid circular cylinder moving along a radial line in a fluid initially at rest. The body is subjected to a rapid displacement of relatively small amplitude in relation to its radius. Both infinite and cylindrically confined fluid domains are considered. Furthermore, non-negligible amplitude motions of the inner cylinder, and viscous and compressible fluid effects are addressed, successively. Different analytical methods and models are used to tackle each of these issues. For motions of non-negligible amplitude of the inner cylinder, a potential flow is assumed and the model, formulated as a two-dimensional boundary perturbation problem, is solved using a regular expansion up to second order. Subsequently, viscous and compressible effects are handled by assuming infinitesimal amplitude motions. The viscous fluid forces are formulated by solving a singular perturbation problem of the first order. Compressible fluid forces are then determined from the wave equation. A nonlinear formulation is obtained for the non-negligible amplitude motion. The viscous and compressible fluid forces, formulated in terms of convolution products, are linked to fluid history effects induced by wave propagation phenomena in the fluid domain. These models are expressed with dimensionless parameters and illustrated for a specific motion imposed on the inner cylinder. The different analytical models permit coverage of a broad range of motions. Hence, for a given geometry and imposed displacement, the appropriate fluid model can be identified and the resulting fluid forces rapidly estimated. The limits of these formulations are also discussed.

Laminar Mixing, Heat Transfer and Pressure Losses in a Chaotic Mini-Channel: Application to the Fuel Cell Cooling

Currently, the heat exchangers allowing the cooling of the low temperature fuel cells (PEMFC) are integrated in the bipolar plates and constituted of a network of straight channels. The flow regime is laminar, and thus, unfavorable to an intense convective heat transfer. In order to increase the power density of the fuel cells, the use of chaotic geometries in the cooling system is envisaged to intensify high convective heat transfer. In this numerical study, several chaotic three-dimensional mini-channels of rectangular section (2 millimeters × 1 millimeter) are evaluated in terms of heat transfer efficiency, mixing properties and pressure losses. Their performances are compared to those of a straight channel geometry currently used in the cooling systems of the PEMFC, and a serpentine 2-D channel. Hydrodynamic and thermal performances of these geometries are computed using the commercial CFD code Fluent©. At the inlet section, the velocity profile is hydrodynamically established. The thermophysical properties of the fluid are constant and equal to those of water at 300 K. The Nusselt number is evaluated for a Reynolds number equal to 200 and with a uniform density flux imposed on the walls and equal to 10,000 W/m2 . For the calculation of the mixing rate, a condition of adiabatic wall is imposed. The inlet section is horizontally divided into two parts. Water in the higher part is at the temperature of 320K and in the lower part is at the temperature of 300K. The calculation of the mixing rate is made for Reynolds numbers equal to 100 and 200. The present study shows that a 3-D chaotic channel geometry significantly improves the convective heat transfer compared to regular straight or serpentine channels. Among all the studied geometries, one of them induces the higher heat transfer intensification (mean Nusselt number equal to 20) with a strong pressure loss. With an alternative geometry, we obtained a better compromise between high heat transfer and reduced pressure loss. However, all the chaotic geometries present similar mixing rate for the two studied Reynolds number. To confirm the performances of the selected geometries, an experimental study is currently undertaken. The final aim is to realize and test a prototype of chaotic heat exchanger in a bipolar plate of PEMFC.© 2006 ASME