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Breakage in particle suspensions

Breakage in particulate systems is a key phenomenon determining the evolution of the particle size and particle properties during processing. This project focuses on the breakage of crystal particles in suspension, as it occurs in solution crystallization. In this process breakage is believed to render the particles to be more spherical, and it is considered to cause the formation of fines and to some extent also secondary nucleation. Many simulations of particulate processes include breakage. These simulations are based on a population balance equation (PBE) which describes the time evolution of the particle population, e. g., the particle size distribution (PSD).
Breakage enters these models as a kinetic process, and usually a first order kinetics is assumed.
Very often, the breakage rate is assumed to be given by a power law expression that relates the breakage rate function to the particle size and the power input from, e. g., the stirrer. This is not sufficient because the parameters in such a breakage model have no physical meaning and there exists no other way for their determination than _tting the model to experimental data. This makes model predictions rather ambiguous and the performance of the model strongly depends on the experiments that have been used for model calibration. This project aims to overcome this deficiency by conducting a fundamental analysis of breakage in particulate suspensions, especially, crystal breakage in suspension. The first part of the project addresses the theoretical development of a physically sound kinetic model for breakage. Breakage kinetics is the results of the frequency with which a certain event occurs (i.e., an impact collision, or the encounter of a particle with an intense turbulent event) multiplied with the probability that breakage occurs during such an event. Two breakage regimes are considered: breakage due to hydrodynamic shear and breakage due to impact. These are the two mechanisms which are relevant for breakage in crystal suspensions.
In the second part, the result of the theoretical development will be applied to describe the evolution of a particle population undergoing breakage, and a PBE model will be formulated to describe the evolution of the PSD. Since the particle properties required to describe breakage might be various, we will adopt a multidimensional PBE (apart from the particle size a proper description of breakage might depend on the shape and the type of the particle, i.e., if the particle is an agglomerate or a single crystal). A suitable numerical scheme will be implemented for solving the PBE model.
In parallel to the theoretical studies of these two parts, the third part addresses the conduction of well designed experiments using a crystalline organic compound will to produce input for model development, and finally it will provide data for model validation. Experimental conditions will be chosen such that breakage is the dominant mechanism and other phenomena, i.e., nucleation, growth and agglomeration are inhibited.

 

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