Direct Measurement of the Reduced Scattering Coefficient by a Calibrated Random Laser Sensor

The research in optical sensors has been largely encouraged by the demand for low-cost and less or non-invasive new detection strategies. The invention of the random laser has opened a new frontier in optics, providing also the opportunity to explore new possibilities in the field of sensing, besides several different and peculiar phenomena. The main advantage in exploiting the physical principle of the random laser in optical sensors is due to the presence of the stimulated emission mechanism, which allows amplification and spectral modification of the signal. Here, we present a step forward in the exploitation of this optical phenomenon by a revisitation of a previous experimental setup, as well as the measurement method, in particular to mitigate the instability of the results due to shot-to-shot pump energy fluctuations. In particular, the main novelties of the setup are the use of optical fibers, a reference sensor, and a peristaltic pump. These improvements are devoted to: eliminating optical beam alignment issues; improving portability; mitigating the variation in pump energy and gain medium performances over time; realizing an easy and rapid change of the sensed medium. The results showed that such a setup can be considered a prototype for a portable device for directly measuring the scattering of liquid samples, without resorting to complicated numerical or analytic inversion procedures of the measured data, once the suitable calibration of the system is performed

A chaotic heat-exchanger for PEMFC cooling applications

High-efficiency cooling systems are key points in PEMFC transport applications, as the volume constraints force the reduction of the stack size while increasing the power density. Moreover, to ensure an optimal electrochemical reaction over the whole polymer membrane surface and hence a maximum efficiency, the temperature field in the cell must be uniform and stay in a narrow range, around 80-90 degrees C. This study focuses on improving the thermal performance of heat-exchangers integrated in the bipolar plates of PEMFCs. The current design of the heat-exchangers in these applications is quite simple; cooling liquid (water) flows in straight channels or serpentines in the rear of the plates. The flow regime is laminar with a Reynolds number around 200. In order to enhance convective heat transfer, we propose here to promote three-dimensional flow inside cooling channels using a novel channel geometry that generates chaotic advection flow. However, to limit the size and the electric resistance of the bipolar plates, the thickness must be severely limited. This work concentrates on developing and characterizing heat-exchangers that can be easily reduced in size while preserving high thermal performance. (c) 2005 Elsevier B.V. All rights reserved

ETRERA Project: an Europe -Tunisia cooperation in S&T transfer

Abstract The project "Empowering Tunisian Renewable Energy Research Activities" (ETRERA) was funded by European Community-FP7 under REGPOT-2009-2 Action, an action finalized to empower the research cooperation in innovatio

A semi-analytical approach to the study of an elastic circular cylinder confined in a cylindrical fluid domain subjected to small-amplitude transient motions

This paper deals with the transient motions experienced by an elastic circular cylinder in a cylindrical fluid domain initially at rest and subjected to small-amplitude imposed displacements. Three fluid models are considered, namely potential, viscous and acoustic, to cover different fluid-structure interaction regimes. They are derived here from the general compressible Navier-Stokes equations by a formal perturbation method so as to underline their links and ranges of validity a priori. The resulting fluid models are linear owing to the small-amplitude-displacement hypothesis. For simplicity, the elastic flexure beam model is chosen for the circular cylinder dynamics. The semi-analytical approach used here is based on the methods of Laplace transform in time, in vacuo eigenvector expansion with time-dependent coefficients for the transverse beam displacement and separation of variables for the fluid. Moreover, the viscous case is handled with a matched asymptotic expansion performed at first order. The projection of the fluid forces on the in vacuo eigenvectors leads to a fully coupled system involving the modal time-dependent displacement coefficients. These coefficients are then obtained by matrix inversion in the Laplace domain and fast numerical inversion of the Laplace transform. The three models, written in the form of convolution products, are described through the analysis of their kernels, involving both the wave propagation phenomena in the fluid domain and the beam elasticity. Last, the three models are illustrated for a specific imposed motion mimicking shock loading. It is shown that their combination permits coverage of a broad range of motions. (C) 2008 Elsevier Ltd. All rights reserved

Energy analysis and optimization of a food defrosting system

International audienceThis paper illustrates the benefits of two energy optimization strategies to improve the overall process efficiency of a food defrosting system. First, an off-line energy analysis, including both the effects of the refrigeration cycle and the fan used to control the cooling air temperature and speed, is carried-out. This first approach puts on display an optimal running point of the process for a specific cooling air temperature value, which leads to an optimization of the overall energy consumption. Second, an on-line energy optimization approach, based on a nonlinear model-based predictive control strategy, is developed. This second approach takes simultaneously into account the expected thawing time, the highest temperature accepted and above all an energetic cost. Simulation results show the benefits of this on-line energy optimization to significantly increase the overall process efficiency. Indeed, this strategy leads to an optimization of the overall energy consumption whatever the expected thawing time and the inlet air temperature

Polymer electrolyte membrane fuel cell characterisation based on current distribution measurements

International audienc

Online FTCS applied to PEMFC water management

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