Catálogo de publicaciones - libros

The gelation of polymer mixtures under constant cooling rate has been found to be an attractive product structuring mechanism for the food industry. As applications become wider, a predictive method for the process is warranted. To this end, we apply the so-called ‘ concept’ in a CFD module for the modeling for microstructure formation of gelling mixtures, where moments of the particle size distribution are evaluated using the local flow conditions as obtained from CFD simulations for the processes considered. The major driving force for these processes is the competition between phase separation, gelation and hydrodynamic phenomena such as break-up and coalescence. Based on theoretical investigations, analytical expressions for the source terms representing the hydrodynamics (break up and coalescence of the droplets) as well as the gelation process were produced. Constitutive models are developed to incorporate the effects of phase separation and gelation on the rheology of the phases. The simulations for different cooling rates clarified the inter-relationships between the competitive mechanisms by depicting the time interval of the domination of each.

We analyze the evolution of a diffusion flame in a turbulent mixing layer. The location of the flame-center is defined by the “stoichiometric” interface. Geometrical properties such as its surface-area, wrinkling and curvature are characterized using an accurate numerical level-set quadrature method. This allows to quantify flame-properties as well as turbulence modulation effects due to coupling between combustion and turbulent transport. We determine the active flame-region which is responsible for the main part of the chemical processing in the flame.

Recently, Burger and Capasso [MAS 11 (2001) 1029–1053] derived a coupled system of partial differential equations to describe non-isothermal crystallization of polymers. The system is based on a spatial averaging of the underlying stochastic birth-and-growth process describing the nucleation and growth of single crystals. Using an appropriate scaling of the original system, we derive a simplified model which only consists of a reaction-diffusion equation with memory for the underlying temperature, such that the degree of crystallization can be explicitly given by a time integration of the temperature-dependent growth and nucleation rate. Numerical simulations indicate that the reduced model shows at least qualitatively the same behavior like the original model.

The aim of this work is to introduce and numerically solve an axisymmetric mathematical model for thermoelectrical simulation of an induction heating furnace.

Thermal explosion of diesel fuel droplets in the presence of thermal radiation is studied. The process is presented in terms of the dynamics of a multi-scale and singularly perturbed system, which is analyzed using the geometrical version of the Method of Integral Manifolds. Analytical estimates of the total ignition delay times in two limiting cases are obtained. The influence of the thermal radiation on the heat transfer and ignition delay time are clarified.

An outline of the Local Defect Correction (LDC) method is given. The method is combined with a procedure to construct an orthogonal, curvilinear fine grid and it is applied to the thermo-diffusive model for laminar flames.

This contribution deals with the mathematical modelling of a high temperature molten carbonate fuel cell (MCFC) and serves as a basis for the following three contributions of this mini-symposium. After a motivation and a short introduction into the working principle of the MCFC, the most important equations of the model are presented. This model is applied for optimisation purposes and as a basis for the derivation of reduced models specifically designed for different tasks.

The reduction of exhaust particulate emissions from diesel vehicles is a great upcoming challenge. As a result of their harmful effects, new legislation on diesel vehicles has been introduced throughout the world specifying low emissionlevels. Today, the use of diesel particulate filter (DPF) in addition to engine modifications is the favoured method to fulfil these criteria. The principle of a DPF is based on the accumulation of particles in the alternating open and closed channels of the filter. The pressure drop over the DPF increases with time. This increase is associated with the rise of fuel consumption. For this reason, the deposited filter cake must be occasionally regenerated. To minimise complex and expensive investigations on test benches, a mathematical model has been developed describing the loading and regeneration behaviour of a DPF. The model is integrated in a commercial CFD-Code using user-defined subroutines (UDS). The CFD-Code was used for the calculation of the fluid flow and the particle tracks of different kinds of particles (e.g. soot, additives) in a two-dimensional model of the DPF. Thus, the axial and radial structure of the deposited particles on the filter can be determined. In the UDS models are implemented to calculate the pressure loss, the separation efficiency and the regeneration behaviour. Comparing the simulation results with the results gained experimentally, it can be seen that both sets of data concur. Further development concerning the implementation of a subroutine to describe the long-term behaviour and transport of the deposited particles will be carried out.

A model was applied on experimental data to study the mass transport of oxygen diffusing through the oil phase and the packaging materials as well as the oxidation reactions. A nonlinear system was numerically solved for various combinations of materials, temperatures, and light availability, by adopting a typical Newton method, in conjunction with a multi-step up-winding finite differences scheme. The probability of the packaged olive oil not to reach the end of its shelf life () and its time evolution, was in very good agreement with the experimental data. was proposed as a reduction indicator for shelf life predictions at “real-life” conditions. Exposure to light at any pattern could significantly stimulate the oxidative degradations, only assisted by elevated temperatures and presence of oxygen. Plastic containers showed particularly higher protective role when oil was stored at light, while glass was the most protective material when oil was stored at dark.

A reduced nonlinear model of a planar molten carbonate fuel cell is presented. The model is derived from a spatially distributed dynamic model of the cell by applying the Karhunen Loève Galerkin procedure. The reduced model is of considerably lower order than the original one and requires much less computation time. The comparison between the two models shows that the reduced model can describe the dynamic of the temperature field with sufficient accuracy and has good extrapolation qualities with respect to changes in the model parameters.