A numerical model able to simulate polymer crystallization under nonisothermal flows is developed. It is based on the assumption that the trace of the extra‐stress tensor, calculated according to a viscoelastic multimode Upper Convected Maxwell (UCM) model, is the driving force of the flow‐induced extra nucleation. Two distinct sets of Schneider equations are used to describe the growth of thermally and flow induced nuclei. The model is then coupled with the momentum equations and the energy equation. As an application, a shear flow configuration between two plates (Couette flow) is simulated. The relative influence of the mechanical and thermal phenomena on the crystallization development as well as the final morphology distribution is then analyzed as a function of the shearing intensity and the cooling kinetics, in terms of nucleation density and crystallite mean sizes. POLYM. ENG. SCI., 50:2044–2059, 2010. © 2010 Society of Plastics Engineers

Polymer nanocomposites offer a great interest as gas barrier materials because of their much-enhanced properties arising from the nanoparticles shape, size, and spatial arrangement within the matrix. However, optimization and further development of such materials requires fundamental understanding of the influence of the nanocomposite structure on permeating gas diffusion. This step can be greatly facilitated through modeling/simulation strategies able to establish relationships between the material microstructure and the achieved enhancement of barrier properties. This review first presents the analytical models developed to estimate the effective diffusivity in polymer nanocomposites. The predictions of the models are analyzed with respect to experimental data reported in the literature and their ability to describe accurately the nanocomposite transport properties when the microstructure complexity increases is discussed. Then, modeling approaches based on numerical simulation techniques (e.g., the finite element method) that allow simulating the diffusion processes and assessing the effect of filler shape, orientation, dispersion, and spatial arrangement are reviewed and discussed. Finally, the importance of 3D simulation strategies for the understanding and prediction of transport properties in the most complex nanocomposite microstructures is addressed.

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Computer simulation is one of the most efficient ways to assist engineers to find a good design solution and to produce high quality plastic parts. The prediction of the parameter evolution during material forming requires a fair understanding of the interaction between the material properties and the process. One of the problems encountered in numerical simulation of the injection molding process is the tracking of the polymerair front or interface during the filling stage (Haagh et al., Int Polym Proc 1997, 12, 207). This article presents a numerical simulation of a nonisothermal molten polymer flow in a cavity as in the injection molding process. The continuity and complete Navier-Stokes equations are coupled with the level set convective equation to predict the flow front and the fountain flow effect. The fluid behavior is modeled by the Cross-Arrhenius model. Thanks to the use of the level set method, a special focus is made on the polymer-mold interfacial heat transfer, and the effect of a variable thermal contact resistance is thoroughly investigated. A new interpretation of the flow marks defect causes, based on the interfacial heat flux analysis, is then suggested.

International audienceA dynamic model for the simulation of a new single-effect water/lithium bromide absorption chiller is developed. The chiller is driven by two distinct heat sources, includes a custom integrated falling film evaporator-absorber, uses mixed recirculation and is exclusively cooled by the ambient air. Heat and mass transfer in the evaporator-absorber and in the desorber are described according to a physical model for vapour absorption based on Nusselt's film theory. The other heat exchangers are handled using a simplified approach based on the NTUeffectiveness method. The model is then used to analyze the chiller response to a step drop of the heat recovery circuit flow rate, and to a sudden reduction of the cooling need in the conditioned space. In the latter case, a basic temperature regulation system is simulated. In both simulations, the performance of the chiller is well represented and consistent with expectations

The optimization of polymer barrier properties is currently of crucial importance for a wide range of applications from packaging to building or even energy applications. To meet the requirements of these applications, polymer matrices are often combined with impermeable (nano) fillers. Different nanofiller natures, shapes, and contents have been experimentally used and a large range of barrier materials has been obtained . In the meantime, several numerical approaches have been developed to model gas diffusion properties of nanocomposite materials. However, these approaches often considered bidimensional systems. The aim of this work is to develop 3D Finite Element Model which would be used to predict gas barrier properties of nanocomposites for disk-shaped nanofillers. The model thus obtained is valid in a wide range of fillers volume fraction values as well as aspect ratios, which makes it possible to go from diluted regimes to semidiluted or even concentrated ones. Furthermore, an analytical equation which describes gas diffusion through nanocomposites films has been built and validated with our finite element modeling model.

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Polymer nanocomposites based on impermeable fillers have been widely developed to improve gas barrier properties. These materials have to be viewed as three phase systems: the matrix, the fillers and an interphase layer between the filler and the matrix. In this paper, the effect of the interphase layer on the overall diffusivity of nanocomposites loaded with impermeable disk-like fillers is analyzed and quantified through 3D finite element modeling of mass diffusion. Ideal ordered filler distributions as well as random filler distributions are considered for filler content in the range 1–20 vol%. A parametric study covering interphase thickness to filler thickness ratio values between 0.125 and 0.5 and interphase diffusivity ratio D interphase/D matrix values from 10−4 to 106 is presented and discussed. The results show that, depending on their quality (weakly or highly diffusive), the presence of interphases can be either beneficial or totally detrimental to the nanocomposite overall barrier properties. A specific case corresponding to the exact compensation of the tortuosity effect by the diffusion in the interphase layer is evidenced and analyzed. Moreover, the effect of continuous diffusion paths, which may occur between overlapping interphases, is investigated. This effect appears to be particularly critical for the barrier performance in the case of highly diffusive interphases. Finally, a confrontation between our simulation approach and an analytical model as well experimental data is proposed.