| Summary: | The shrinkage and cracking of filter cakes during deliquoring is an undesired phenomenon frequently encountered in the pharmaceutical industry. When a cake cracks, a channel is formed which can propagate through the body of the filter cake, down to the filter medium, often developing into a network of cracks that sometimes results in the exposition of the filter medium. The gas flows preferentially through these cracks, instead of removing the liquid from the pores of the filter cake. This significantly reduces the effectiveness of the deliquoring process, which results in an increased gas consumption, high residual moisture content, and the requirement for an increased thermal energy input in later drying stages. Studies to date have been scant, and the problem tends to be treated in a phenomenological manner. In Chapter 1 (Filtration overview), filtration theory will be presented, looking at flow through porous media, compressibility, and the influence of parameters such as particle size and sedimentation. Other factors which are rarely considered in constitutive equations, such as flocculation and sidewall friction will also be presented, as will the effects of the stresses and strains that develop once capillary entry pressure has been exceeded and liquid is displaced by gas in the pores of the filter cake. Chapter 2 (Literature review) will be an overview of other studies of filter cake cracking, and also cracking in other contexts such as that encountered in colloidal films and concrete structures. Following a description of experimental methodology (Chapter 3), experimental results from the parametric studies that form the basis of this thesis will be presented. Chapter 4 (macroscopic level) will be an investigation into the effects of pressure, aspect ratio, concentration and settling. Chapter 5 (material properties) will focus on particle size distribution & viscosity. Chapter 6 will conclude this section with an investigation into the molecular level (surfactants, adsorption, etc). Results will be presented in the form of graphs and correlations between the investigated parameters and key performance indicators, mainly the presence or absence of cracking, permeability ratio and residual moisture content. Future work should investigate other solid materials of different shapes and size distributions, as well as septum media.
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