To cool down the stack system in polymer electrolyte fuel cells (PEFCs), a coolant is needed that must be electrically nonconductive. In the specialized coolant that is modeled by us, charged nanoparticles are added into the flow to neutralize the ion contamination that otherwise gradually degrades the coolant until shunt currents become significant. A computational fluid dynamics (CFD) physicochemical model of the multiphase coolant flow with charged nanoparticles has been formulated and coded using COMSOL Multiphysics and MEMS. Electrochemistry, fluid mechanics, steric stabilization, and heat transfer are coupled in this model. For nanoparticles in the fluid, electrokinetic force, electrical double layer (EDL) force, hydrodynamic force, and buoyancy force have been taken into account for the prediction of the electrodeposition rate onto channel walls. The overall goal of the model is to provide a fundamental first principles-based design tool for a specialized coolant to enable operations in a fuel cell stack for 2−3 years without the need for frequent replacement or filtering of the coolant.

In this paper, we present a new analog set-up for non linear dielectric measurements. The device is based on the auto-balanced bridge principle used in impedance analyzers. Its main advantage is to operate at high frequencies in comparison with a classical current amplifier. This extension consists in extracting the harmonics of a non sinusoidal current crossing the material. The set-up is used to perform non linear dielectric measurements on a ferroelectric liquid crystal and shows better performances than a previously published digital set-up.

We present a derivation of the time evolution equation of a physical quantity defined as an integral of a density over a moving surface. The equation can be readily used to obtain the transport equation for an interfacial entity such as surfactants on the surface of a single-valued interface as in thin films. By utilizing the concept of the extension field of the density we generalize the transport equation to the case of multi-valued interfaces.

Wall slip and wall divergence are known to have large and opposing effects on the stability of flow in a two-dimensional channel. While divergence hugely destabilises, slip dramatically stabilizes the linear mode. In a non-parallel stability analysis, we study a combination of these two effects, since both will coexist in small-scale flows with wall roughness. Our main results are (i) that the stabilising effect of slip is reversed at higher angles of divergence, (ii) transient growth of disturbances is unaffected by either wall-divergence, or by slip at any divergence. Moreover, at the Reynolds numbers relevant here, transient growth is too low to be a significant player in transition to turbulence, which is more likely to be driven by linear instability. The results would have implications for the onset of unsteadiness and mixing in small scale flows.

In order to improve our knowledge of the emitted signal of forests at L-band (1.4 GHz) we focused this study on permittivity measurements of heterogenic natural media such as soil or litter consisting of plant debris and organic matter. This study was done in the context of the upcoming SMOS (Soil Moisture and Ocean Salinity) satellite mission that will attempt to map surface soil moisture from L-band (1.4 GHz) passive microwave measurements. In the field of passive microwaves, very little information exists about the behaviour of the L-band signal of forests especially when litter is included in the soil-vegetation system. To date very few analyses have investigated the dielectric behaviour of the litter layer and its influence on the microwave emission of forests is generally neglected.

This paper presents a dynamical non linear model of the spatial time-dependant evolution of A3 point during a particular sequence of resistance spot welding in steel material. The model is based on a solution to the heat equation, expressed in cylindrical coordinates inside the joint area, and when the source term is attributed to the electrical power. By the mean of the steel binary Fe–C diagram and the deduced t-dependant temperature rise profile, an estimation of the A3 point spatial range date is given and compared to further results. The obtained temperature profile is yielded, taking into account main parameters variations, as a guide to non-destructive protocols and thermal characteristics investigation