Dynamics of bubble and drop breakup in turbulent flows have been studied in detail, using a high‐speed CCD camera. Analysis of breakup times, deformations, deformation velocities, number of fragments, and the resulting daughter size distributions show that there are several important differences in the breakup mechanism of bubbles and drops. It is shown that the increase in interfacial energy prior to breakup exceeds the increase after breakup. The use of an activation barrier that better describes the turbulent structures that can interact with fluid particles and also cause breakup is proposed. Measurements under identical hydrodynamic conditions reveal that an internal flow redistribution mechanism is responsible for generation of unequal‐sized bubble fragments. Due to the three orders of magnitude higher density of liquids than of gases, this mechanism does not occur for drops. The measurements also show that assumption of binary breakup is reasonable for bubbles but not for drops. © 2006 American Institute of Chemical Engineers AIChE J, 2006

Computational fluid dynamics, CFD, has become an indispensable tool for many engineers. This book gives an introduction to CFD simulations of turbulence, mixing, reaction, combustion and multiphase flows. The emphasis on understanding the physics of these flows helps the engineer to select appropriate models to obtain reliable simulations. Besides presenting the equations involved, the basics and limitations of the models are explained and discussed. The book combined with tutorials, project and power-point lecture notes (all available for download) forms a complete course. The reader is given hands-on experience of drawing, meshing and simulation. The tutorials cover flow and reactions inside a porous catalyst, combustion in turbulent non-premixed flow, and multiphase simulation of evaporation spray respectively. The project deals with design of an industrial-scale selective catalytic reduction process and allows the reader to explore various design improvements and apply best practice guidelines in the CFD simulations.

A method that enables accurate determination of contact resistances in thermoelectric generators and which gives detailed insight into how these reduce module performance is presented in this paper. To understand the importance taking thermal and electrical contact resistances into account in analysis of thermoelectric generators, full-scale modules were studied. Contact resistances were determined by means of non-linear regression analysis on the basis of results from 3D finite element simulations and experiments in a setup in which heat flow, voltage, and current were measured. Statistical evaluation showed that the model and the identified contact resistances enabled excellent prediction of performance over the entire range of operating conditions. It was shown that if contact resistances were not included in the analysis the simulations significantly over-predicted both heat flow and electric power output, and it was concluded that contact resistance should always be included in module simulations. The method presented in this paper gives detailed insight into how thermoelectric modules perform in general, and also enables prediction of potential improvement in module performance by reduction of contact resistances.

A solid introduction to mathematical modeling for a range of chemical engineering applications, covering model formulation, simplification and validation. It explains how to describe a physical/chemical reality in mathematical language and how to select the type and degree of sophistication for a model. Model reduction and approximation methods are presented, including dimensional analysis, time constant analysis and asymptotic methods. An overview of solution methods for typical classes of models is given. As final steps in model building, parameter estimation and model validation and assessment are discussed. The reader is given hands-on experience of formulating new models, reducing the models and validating the models. The authors assume the knowledge of basic chemical engineering, in particular transport phenomena, as well as basic mathematics, statistics and programming. The accompanying problems, tutorials, and projects include model formulation at different levels, analysis, parameter estimation and numerical solution.