Influence of polymer viscoelasticity on the residence distributions of extruders

Thermomechanical Fractional Model of Two Immiscible TEMHD

We introduce a mathematical model of unsteady thermoelectric MHD flow and heat transfer of two immiscible fractional second-grade fluids, with thermal fractional parametersαiand mechanical fractional parametersβi,i=1,2. The Laplace transform with respect to time is used to obtain the solution in the transformed domain. The inversion of Laplace transform is obtained by using numerical method based on a Fourier-series expansion. The numerical results for temperature, velocity, and the stress distributions are represented graphically for different values ofαiandβi. The graphs describe the fractional thermomechanical parameters effect on the case of two immiscible fluids and the case of a single fluid.

Mechanistic modeling of modular co-rotating twin-screw extruders

In this study, we present a one-dimensional (1D) model of the metering zone of a modular, co-rotating twin-screw extruder for pharmaceutical hot melt extrusion (HME). The model accounts for filling ratio, pressure, melt temperature in screw channels and gaps, driving power, torque and the residence time distribution (RTD). It requires two empirical parameters for each screw element to be determined experimentally or numerically using computational fluid dynamics (CFD). The required Nusselt correlation for the heat transfer to the barrel was determined from experimental data. We present results for a fluid with a constant viscosity in comparison to literature data obtained from CFD simulations. Moreover, we show how to incorporate the rheology of a typical, non-Newtonian polymer melt, and present results in comparison to measurements. For both cases, we achieved excellent agreement. Furthermore, we present results for the RTD, based on experimental data from the literature, and found good agreement with simulations, in which the entire HME process was approximated with the metering model, assuming a constant viscosity for the polymer melt.

Residence Time Distribution in a High Shear Twin Screw Extruder

The residence time distributions (RTD) of a high shear twin screw extruder were measured by an on–line UV fluorescence device. First, by increasing throughput (Q) and screw speed (N), a decrease of the complex viscosity of the studied polypropylene (PP) was observed, revealing chain scissions. It was associated to high viscous dissipation taking place during extrusion, and more particularly under high shear conditions. Then the impact of these experimental conditions on the RTD was carried out. As expected, an increase of usual throughputs and screw speeds decrease mostly the RTD characteristic data. In this study industrial rate have been studied: throughput varied from 1.5 up to 22 kg h−1 and screw speed varied from 200 min−1 up to 1 200 min−1. However, by increasing the screw speed over usual values (from 500 up to 1 200 min−1), the variation of some experimental RTD characteristics were unexpected. Indeed, the slope of the shape of the experimental RTD function E(t) changed significantly. This phenomenon will be called lag or delay time. This result was only observed at low throughputs and high screw rotation speeds. To finish, a modeling software of twin screw extrusion process was used to compare experimental and calculated results. For usual processing conditions (up to 700 min−1), the simulation predicts nicely the experimental RTDs. However, at high screw speed (N > 800 min−1) and moderate throughput (Q = 4 kg h−1), the simulation fails to predict the RDT delay time. Hence, some side effects apparently occurred during high shear extrusion at low throughputs.