Application of a multiscale approach for modeling the rheology of complex fluids in industrial mixing equipment

Many industrial sectors, like the personal care one, make wide use of mixing processes that involve complex fluids. However, modeling the rheology of these fluids is still challenging due to their non-Newtonian behavior, which depends also on the local composition. Computational tools such as dissipative particle dynamics (DPD) have been already used to calculate the equilibrium properties of these systems. Moreover, different works have been focused on the calculation of transport properties from these mesoscale DPD simulations. Multiscale approaches have been proposed to couple rheological information from DPD with computational fluid dynamics (CFD) simulations. The CFD technique reproduces the macroscale piece of equipment, implementing a rheology model built using the Gaussian process regression, a mathematical tool related to machine learning. In this work, such a framework is tested on an industrial process, to assess its performance on a realistic application. The investigated system is a solution at a high concentration of sodium lauryl ether sulfate in water under laminar fluid dynamics regime. The results show that the mixture correctly exhibits a shear-thinning behavior and presents viscosity values in good agreement with rheology experiments. While the feasibility of the coupling approach is shown, further studies on DPD are needed to improve the accuracy and the predictability of the methodology

Simulation of high Schmidt number fluids with dissipative particle dynamics: Parameter identification and robust viscosity evaluation

Dissipative particle dynamics (DPD) is a widely used coarse-grained technique for the simulation of complex fluids. Although the method is capable of describing the hydrodynamics of any fluid, the common choice of DPD parameters, such as friction coefficient γ, dissipative cutoff radius , coarse-graining factor Nm and weighting function exponent s, unrealistically leads to the simulation of liquid water with a low Schmidt number Sc at standard pressure and temperature. In this work we explored the influence of these parameters, finding the set of parameters needed to properly simulate liquid water. Particular attention was devoted to the numerical techniques to calculate the transport properties from equilibrium simulations, especially in the calculation of the viscosity, comparing the most commonly adopted techniques and formulating a recipe that can be used for further investigations

Heat exchanger/reactors (HEX reactors): Concepts, technologies: State-of-the-art

Process intensification is a chemical engineering field which has truly emerged in the past few years and is currently rapidly growing. It consists in looking for safer operating conditions, lower waste in terms of costs and energy and higher productivity; and away to reach such objectives is to develop multifunctional devices such as heat exchanger/reactors for instance. This review is focused on the latter and makes a point on heat exchanger/reactors. After a brief presentation of requirements due to transposition from batch to continuous apparatuses, heat exchangers/reactors at industrial or pilot scales and their applications are described

Application of Gaussian cubature to model two-dimensional population balances

In many systems of engineering interest the moment transformation of population balance is applied. One of the methods to solve the transformed population balance equations is the quadrature method of moments. It is based on the approximation of the density function in the source term by the Gaussian quadrature so that it preserves the moments of the original distribution. In this work we propose another method to be applied to the multivariate population problem in chemical engineering, namely a Gaussian cubature (GC) technique that applies linear programming for the approximation of the multivariate distribution. Examples of the application of the Gaussian cubature (GC) are presented for four processes typical for chemical engineering applications. The first and second ones are devoted to crystallization modeling with direction-dependent two-dimensional and three-dimensional growth rates, the third one represents drop dispersion accompanied by mass transfer in liquid-liquid dispersions and finally the fourth case regards the aggregation and sintering of particle populations

Aggregation efficiency of amorphous silica nanoparticles

Przedstawiono wyrażenie na efektywność zderzeń bazujące na analizie charakterystycznych skal czasowych procesu agregacji nanocząstek krzemionki. Pozwala to na wytłumaczenie istnienia obszaru metastabilnego dla koloidalnej krzemionki oraz powolnego żelowania w tym obszarze, mimo bliskości punktu izoelektrycznego. Zaproponowany opis matematyczny może być wykorzystany do wyznaczenia szybkości agregacji cząstek krzemionki koloidalnej w zależności od parametrów procesowych oraz charakterystycznych właściwości populacji cząstek.In this work expression for the collision efficiency was proposed based on the analysis of characteristic time scales of the aggregation process of silica nanoparticles. It allows us to ехріаіп the existence of metastable region of the colloidal silica and slow gelation in that region regardless of the vicinity of isoelectric point. The developed expression can be further used to determine the aggregation rate depending on the process parameters and characteristic properties of considered population of particles when used together with suitable collision kemel

Experimental and numerical investigations of jet mixing in a multifunctional channel reactor: Passive and reactive systems

Mixing of two liquids in a new multifunctional channel reactor developed by AlfaLaval has been studied both experimentally and through computational fluid dynamics (CFD). As the channels are quite narrow the Reynolds numbers are low and the bulk of the channel is within the turbulent boundary layer. This makes accurate a priori predictions of the flowfield difficult and experimental validation necessary. Particle image velocimetry (PIV) was used to measure the flowfield, whereas planar laser-induced fluorescence was used for a scalar concentration field. CFD simulations were performed with the commercial software Fluent 5.5. Different turbulence models were tested and compared with PIV. The best predictions were obtained with a low Reynolds boundary layer k-ε turbulence model. Mixing of a passive tracer, including mean concentration and concentration variance, was calculated with the turbulent mixer model of Baldyga. A reactive system with diazo coupling between 1-naphthols, 2-naphthols and diazotized sulphanilic acid was studied both experimentally and theoretically due to its sensitivity to mixing conditions. The interpolation model of Baldyga was used to predict the evolution of the species. Good agreement was found between simulations and experiments for both the flow field and the reactive system

Experimental and numerical investigations of jet mixing in a multifunctional channel reactor: Passive and reactive systems

Mixing of two liquids in a new multifunctional channel reactor developed by AlfaLaval has been studied both experimentally and through computational fluid dynamics (CFD). As the channels are quite narrow the Reynolds numbers are low and the bulk of the channel is within the turbulent boundary layer. This makes accurate a priori predictions of the flowfield difficult and experimental validation necessary. Particle image velocimetry (PIV) was used to measure the flowfield, whereas planar laser-induced fluorescence was used for a scalar concentration field. CFD simulations were performed with the commercial software Fluent 5.5. Different turbulence models were tested and compared with PIV. The best predictions were obtained with a low Reynolds boundary layer k-ε turbulence model. Mixing of a passive tracer, including mean concentration and concentration variance, was calculated with the turbulent mixer model of Baldyga. A reactive system with diazo coupling between 1-naphthols, 2-naphthols and diazotized sulphanilic acid was studied both experimentally and theoretically due to its sensitivity to mixing conditions. The interpolation model of Baldyga was used to predict the evolution of the species. Good agreement was found between simulations and experiments for both the flow field and the reactive system