arXiv subjects

Alain Sommier

Publications and source records attributed to Alain Sommier.

4 recordsLinked to original sources

arXiv2025

Measuring thermal contact resistances between metallic rods using laser spot heating and infrared thermography. Part 1

Estimation of thermal contact resistances between cylinders can be achieved using heating on the cross sections by a laser spot and measurement of the temperature response by IR thermography. This type of measurement makes it possible to characterise contacts in clusters of cylinders to simulate clusters of grains, or the properties of fibrous media in the transverse direction or, under certain conditions, to detect emerging thermal resistances (cracks perpendicular to the observation plane) by IR thermography. Here, the thermal model is simplified because the temperature field in relaxation on either side of the resistance can be considered isothermal with a separation of transfers in the plane and along the thickness. The mathematical model is then analytical (relaxation of a linear system), and the processing of the temperature field can be inversed thanks to the consideration of the logarithm of matrices, useful when studying the propagation of measurement noise. The method proposed in the case of two or three cylinders is a first step and a validation for applications to the study of more complex media (large number of cylinders, granular media).

physics.med-ph↗

arXiv2023

Imaging concentration fields in microfluidic fuel cells as a mass transfer characterization platform

Microfluidic fuel cells (MFCs) are microfluidic electrochemical conversion devices that are used to power small pieces of electrical equipment. Their performance relies on the improvement of the mass transfer of the reactants at the electrode interface. {In this work, a MFC is developed to implement a novel imaging technique that allows the measurement of reactant concentration fields, featuring formic acid as the fuel and potassium permanganate as the oxidant. The concentration fields were imaged } based on transmitted visible spectroscopy, which links the light intensity passing through the MFC to its local reactant concentration. {An analytical model was developed to estimate the mass diffusivity and kinetic reaction rate coefficient. For the first time, mass transport and transfer coefficient were simultaneously measured during operation. These parameters estimated using the proposed technique can be implemented in a numerical model to predict the MFC performance and concentration distribution. This work paves the way toward advanced imaging tools for operando mass transfer characterizations in microfluidics and Tafel kinetic characterization in many electrochemical devices.

physics.chem-ph↗

arXiv2023

Infrared thermotransmittance-based temperature field measurements in semitransparent media

Temperature field contactless measurements in or at the surfaces of semitransparent media are a scientific challenge, as classical thermography techniques based on proper material emission cannot be used. In this work, an alternative method using infrared thermotransmittance for contactless imaging temperatures is proposed. To overcome the weakness of the measured signal, a lock-in acquisition chain is developed, and an imaging demodulation technique is used to retrieve the phase and amplitude of the thermotransmitted signal. These measurements, combined with an analytical model, enable the estimation of the thermal diffusivity and conductivity of an infrared semitransparent insulator (wafer of borofloat 33 glass) as well as the monochromatic thermotransmittance coefficient at 3.3 um. The obtained temperature fields are in good agreement with the model, and a detection limit of $\pm 2^{\circ}$ C is estimated with this method. The results of this work open new opportunities in the development of advanced thermal metrology for semitransparent media.

physics.app-ph↗

arXiv2022

Semianalytical mass transfer impedance model in microfluidic electrochemical chips

In this paper we report a semianalytical model of the mass transfer impedance in microfluidic electrochemical chips (MEC). It is based on the molar advection diffusion equation in a microfluidic channel with a Poiseuille flow and an electrochemical reaction at the interface of deposited electrodes. Using the Fourier-Laplace integral transforms and the quadrupole formalism, a solution to these equations is found and the three dimensional (3D) transient concentration and current density fields are computed. This solution is validated using MFC operando concentration fields measured by visible spectroscopic imaging technique, and several equivalent electrical circuits are also proposed to model the mass transfer in MEC. This work reports the fastest way to compute the 3D transient mass transfer impedance which can be used in large variety of applications such as MEC based cytometry measurements or fuel cell current density prediction.

physics.chem-ph↗