Clogging transition induced by self filtration in a slit pore

International audienceParticles that flow through porous environments like soils, inside a filter or within our arteries, often lead to pore clogging. Even though tremendous efforts have been made in analysing this to circumvent this issue, the clog formation and its dynamics remain poorly understood. Coupling two experimental techniques, we elucidate the clogging mechanism at the particle scale of a slit pore with its height slightly larger than the particle diameter. We identify all the particle deposition modes during the clog formation and accurately predict the corresponding deposition rate. We show how the geometrical features of the pores and the competition between deposition modes can profoundly change the clog morphology. We find that the direct capture of particles by the pore wall is rather limited. The clog formation is more closely related to the short range hydrodynamic interaction between flowing particles and those which are already immobilized within the pore. Finally we demonstrate that all the clogging regimes can be gathered on a single phase diagram based on the flow conditions and the filter design. © The Royal Society of Chemistry

Flow decline during pore clogging by colloidal particles

International audienceThe flow of colloidal suspensions through porous media often leads to the deposition of particles inside the pores which increases the local hydrodynamic resistance by narrowing the pore space available and modifying the flow path of the transported particles. There is a significant flow decline in the extreme case when the entire porous medium becomes clogged. However, there are no experimental studies that determine directly the amplitude of this flow decline when compared with the dynamics of the formation of the particle deposit. This is mainly due to the great challenge of gaining experimental access to the features of the internal structure of the deposit as it grows and thus the ability to determine the flow inside it. In this paper, we show that is possible to monitor the flow decline corresponding to the successive deposition of colloidal particles inside a constriction (pore), ending by its complete blocking. The variation of the flow is determined by the measurement of the velocity of the particles through our channel. Such a technique coupled to the precise knowledge of what is deposited inside the pore, thanks to image analysis, enables us to determine the different contributions to the flow decline. We also use numerical simulations to access the flow inside the porous structure of the deposit as it grows. Together, experiments and simulations demonstrate that the obstruction process and the subsequent limited growth of the clog, corresponding to a few layers of accumulated particles, have a higher impact on the amplitude of the flow decline than the extra growth of the clog

Structure and flow conditions through a colloidal packed bed formed under flow and confinement

International audienceWhen a colloidal suspension flows in a constriction, particles deposit and are able to clog it entirely, this fouling process being followed by the accumulation of particles. The knowledge of the dynamics of formation of such a dense particle assembly behind the clog head and its structural features is of primary importance in many industrial and environmental processes and especially during filtration. While most studies concentrate on the conditions under which pore clogging occurs, i.e., the pore narrowing up to its complete obstruction, this paper focuses on the accumulation of particles that follows pore obstruction. We determine the relative contribution of the confinement dimensions, the ionic strength and the flow conditions on the permeability and particle volume fraction of the resultant accumulation. In high confinement the irreversible deposition of particles on the channel surfaces controls the structure of the accumulation and the flow through it, irrespective of the other conditions, leading to a Darcy flow. Finally, we show that contrarily to the clog head, in which there is cohesion between particles, those in the subsequent accumulation are held together by the fluid and form a dense suspension of repulsive hard spheres

Dynamics of pore fouling by colloidal particles at the particle level

International audienceParticle filtration occurs whenever particles flow through porous media such as membrane. Progressive capture or deposition of particles inside porous structure often leads to complete, and generally unwanted, fouling of the pores. Previously there has been no experimental work that has determined the particle dynamics of such a process at the pore level, since imaging the particles individually within the pores remains a challenge. Here, we overcome this issue by flowing fluorescently dyed particles through a model membrane, a microfluidic filter, imaged by a confocal microscope. This setup allows us to determine the temporal evolution of pore fouling at the particle level, from the first captured particle up to complete blocking of the pore. We show that from the very beginning of pore fouling the immobile particles inside the pore significantly participate in the capture of other flowing particles. For the first time it is determined how particles deposit inside the pore and form aggregates that eventually merge and block the pore

Pore cross-talk in colloidal filtration

International audienceBlockage of pores by particles is found in many processes, including filtration and oil extraction. We present filtration experiments through a linear array of ten channels with one dimension which is sub-micron, through which a dilute dispersion of Brownian polystyrene spheres flows under the action of a fixed pressure drop. The growth rate of a clog formed by particles at a pore entrance systematically increases with the number of already saturated (entirely clogged) pores, indicating that there is an interaction or “cross-talk” between the pores. This observation is interpreted based on a phenomenological model, stating that a diffusive redistribution of particles occurs along the membrane, from clogged to free pores. This one-dimensional model could be extended to two-dimensional membranes