Modelling the breakup of solid aggregates in turbulent flows

The breakup of solid aggregates suspended in a turbulent flow is considered. The aggregates are assumed to be small with respect to the Kolmogorov length scale and the flow is assumed to be homogeneous. Further, it is assumed that breakup is caused by hydrodynamic stresses acting on the aggregates, and breakup is therefore assumed to follow a first-order kinetic where KB(x) is the breakup rate function and x is the aggregate mass. To model KB(x), it is assumed that an aggregate breaks instantaneously when the surrounding flow is violent enough to create a hydrodynamic stress that exceeds a critical value required to break the aggregate. For aggregates smaller than the Kolmogorov length scale the hydrodynamic stress is determined by the viscosity and local energy dissipation rate whose fluctuations are highly intermittent. Hence, the first-order breakup kinetics are governed by the frequency with which the local energy dissipation rate exceeds a critical value (that corresponds to the critical stress). A multifractal model is adopted to describe the statistical properties of the local energy dissipation rate, and a power-law relation is used to relate the critical energy dissipation rate above which breakup occurs to the aggregate mass. The model leads to an expression for KB(x) that is zero below a limiting aggregate mass, and diverges for x → ∞. When simulating the breakup process, the former leads to an asymptotic mean aggregate size whose scaling with the mean energy dissipation rate differs by one third from the scaling expected in a non-fluctuating flo

Flow Structure, Drop Deformation and Mass Transfer in Dense Emulsions

This paper presents applications of a new model of the rheological behaviour of dense oil-inwater emulsions of non-colloidal droplets to describe the flow structure, the effects of the flow of dense emulsion on drop deformation and the related increase of the interfacial area and the mass transfer rate

Flow Structure, Drop Deformation and Mass Transfer in Dense Emulsions

This paper presents applications of a new model of the rheological behaviour of dense oil-inwater emulsions of non-colloidal droplets to describe the flow structure, the effects of the flow of dense emulsion on drop deformation and the related increase of the interfacial area and the mass transfer rate

Large eddy simulation of precipitation process carried out in jet reactors

The paper presents an application of large eddy simulations to predict a course of precipitation process carried out in selected types of jet reactors. In the first part of this work the simulations results were validated using PIV and PLIF techniques and also by comparing model predictions with experimental data for fast parallel chemical test reactions. In the second part of this work predictions of modeling are compared with experimental data for BaSO4 precipitation. Precipitation model is tested in this part also by comparing predictions of the model based on LES with results obtained using the multiple-time-scale mixing model combined with the k‒e model

A multi-layered view of chemical and biochemical engineering

The contents of this article are based on the results of discussions the corresponding author has had since 2015 with the co-authors, who are members of academia and industry in Europe, on the scope and significance of chemical and biochemical engineering as a discipline. The result is a multi-layered view of chemical and biochemical engineering where the inner-layer deals with the fundamental principles and their application; the middle-layer deals with consolidation and expansion of the principles through a combination of science and engineering, leading to the development of sustainable technologies; and the outer-layer deals with integration of knowledge and collaboration with other disciplines to achieve a more sustainable society. Through this multi-layered view several important issues with respect to education, research and practice are highlighted together with current and future challenges and opportunities

Selected methods of describing rheological properties during mixing®

Artykuł przedstawia przegląd metod opisu właściwości reologicznych substancji podczas mieszania w przemyśle produkcji żywności. Scharakteryzowano zasady reometrii mieszadłowej oraz metody wyznaczania naprężenia ścinającego i szybkości ścinania w mieszalnikach zaopatrzonych w mieszadła o różnej konstrukcji. Podano ponadto zalety i ograniczenia stosowania reguł reometrii mieszadłowej.The article presents an overview of methods for the description of rheological properties of substances during mixing in the food production industry. The rules of mixer-type rheometry and methods of determining shear stress and shear rate in mixers equipped with various designs agitators were characterized. The advantages and limitations of the use of mixer-type rheometry rules are also given

Application of new chemical test reactions to study mass transfer from shrinking droplets and micromixing in the rotor-stator mixer

A pair of fast competitive reactions, neutralization and 2,2-dimetoxypropane (DMP) hydrolysis, has been applied do study mass transfer and micromixing in a T 50 Ultra-Turrax® - IKA rotor-stator device. In experiments the dispersed organic phase containing p-Toluenesulfonic acid (pTsOH) dissolved in diisopropyl ether, whereas the continuous phase was represented by the aqueous solution of sodium hydroxide, 2,2-dimetoxypropane (DMP) and ethanol. During mixing a fast mass transfer of a solute (pTsOH) from organic phase droplets, which were shrinking due to fast dissolution of the organic solvent, was followed by micromixing and chemical reactions in the continuous phase. Measured hydrolysis yields were applied to express effects of mixing on the course of chemical reactions. Modeling was based on application of models describing drop breakup, mass transfer in the liquid-liquid system and micromixing. Combined effects of mass transfer and drop breakage on drop population were expressed using the population balance equations. The model has been used to interpret experimental results, in particular to identify the efficiency of mixing

Energetic efficiency of mass transfer accompanied by chemical reactions in liquid-liquid systems

Energetic efficiency depicting the fraction of energy dissipation rate used to perform processes of drop breakup and mass transfer in two-phase, liquid-liquid systems is considered. Results of experiments carried out earlier in two types of high-shear mixers: an in-line rotor-stator mixer and a batch rotor-stator mixer, have been applied to identify and compare the efficiency of drop breakage and mass transfer in both types of mixers. The applied method is based on experimental determination of both: the product distribution of chemical test reactions and the drop size distributions. Experimental data are interpreted using a multifractal model of turbulence for drop breakage and the model by Favelukis and Lavrenteva for mass transfer. Results show that the energetic efficiency of the in-line mixer is higher than that of the batch mixer; two stator geometries were considered in the case of the batch mixer and the energetic efficiency of the device equipped with a standard emulsor screen (SES) was higher than the efficiency of the mixer equipped with a general purpose disintegrating head (GPDH) for drop breakup but smaller for mass transfer