Using DEM-CFD method at colloidal scale

The aim of this work is to look into the applicability of Discrete Element Modelling (DEM) coupled to Computational Fluid Dynamics (CFD) to simulate micro-scale colloidal particles immersed in fluid. Numerical methods were implemented through the commercial framework of EDEM2.3. As opposed to dissolved matter, which behaves as a continuum within the fluid medium, particulate matter is made of discrete entities that interact amongst themselves, and with the fluid and any physical boundaries. Particulate matter is ubiquitous in many purification processes that would beneficiate from having an easy way to model particle dynamics immersed in water. In an effort to understand better the dynamics of particle deposition under surface forces and hydraulic forces, a micro-scale numerical model was built adopting both a mechanistic and a statistical approach to represent the forces involved in colloidal suspension. The primary aim of the model was to simulate particle aggregation, deposition and cluster re-suspension in real world micro-systems. Case studies include colloidal flocculation in a constricted tube, and colloidal fouling around membrane filtration feed spacers. This work used a DEM-CFD coupling method that combined the DEM particle flow simulation with hydrodynamics forces from a velocity field computed through CFD. It also implemented boundary-particle and particle-particle interactions by enabling the modelling of surface and interfacial forces. Two kinds of coupling method were considered: two-way and one-way coupling. Two-way coupling is suitable for high particle concentration flow where particle loading affects the hydrodynamics. One-way coupling is suitable for dispersed particle configuration where the flow field is assumed to be undisturbed by the particles. The advantages and drawbacks of both techniques for micron-size particles were investigated. EDEM 2.3 was customised with plug-ins to implement Van der Waals forces and Brownian forces and its post-processing features offered the ability to investigate easily the microparticles behaviour under the influence of fluid forces. In this context, DEM-CFD modelling using EDEM 2.3 represents an improvement on previously published works as it enables higher visibility and reproducibility along with increasing the number of potential users of such modelling. Emphasis was given in presenting original findings and validation results that illustrate DEMCFD applicability, with respect to modelling of hydraulically mediated colloidal surface interaction; while highlighting factors that limit the ability of the technique. For instance, the effect of particle disturbance on the surrounding medium currently proves difficult to model

Colonial Metaphors: Symbolic Approaches to the Chaco Tierra Adentro

La expresión tierra adentro pertenece al vocabulario de las fuentes coloniales y es también utilizada en el ámbito académico para los estudios de frontera; sin embargo, aún no hemos reflexionado sobre sus usos y sentidos. En este trabajo adopto una perspectiva etnográfica orientada a las fronteras del Chaco durante el siglo XVIII, con la intención de abordar la dimensión simbólica de tierra adentro, atendiendo a los distintos sentidos adheridos a ella durante la Colonia y a las prácticas de dominación asociadas a esas significaciones. Considero, también, su incorporación como categoría de análisis a los estudios académicos sobre los espacios de frontera. Los datos provienen de un gran número de documentos escritos durante la Colonia y fueron examinados desde la propuesta de la antropología histórica: la crítica textual y contextual, la lectura transversal y la interpretación de las situaciones sociales del pasado, entre otras. Tierra adentro condensa un amplio abanico de significados arraigados en el imaginario colonial, que condicionaron la percepción de los grupos indígenas no sometidos y de sus territorios; esos significados ?que se expresan en términos metafóricos? promovieron y habilitaron políticas de sometimiento; el uso de esta expresión en el ámbito académico va de la mano de cierta conceptualización sobre la tierra adentro sobre la que recién se ha comenzado a reflexionar. Este trabajo aporta a la desnaturalización de una expresión habitualmente utilizada, pero sobre cuyos significados intrínsecos aún no se han formulado definiciones ni debates. De esta manera, contribuye a la discusión crítica en cuanto al uso y los alcances teóricos del vocabulario heredado de las fuentes documentales para la investigación histórico-antropológica y propone algunos aspectos comunes que podrían aplicarse a otros espacios concebidos como tierra adentro durante la experiencia colonial.The expression tierra adentro belongs to the language of colonial sources and although it is also used in academia in border studies, we are yet to reflect on its uses and meanings. In this work, I adopt an ethnographic perspective focusing on the frontiers of the Chaco province during the 18th century, in order to address the symbolic dimension of the tierra adentro, paying attention to the different meanings attached to it during the colonial period and the practices of domination associated with those meanings. I also consider its incorporation as a category of analysis in academic border studies. The data come from a large number of documents written during the colonial period, which I examined based on historical anthropology approach: Textual and contextual criticism, transversal reading, and interpretation of past social situations, among others. Tierra adentro condenses a wide range of meanings rooted in the colonial imaginary, which conditioned the perception of non-submissive indigenous groups and their territories; these meanings —expressed in metaphorical terms— promoted and enabled policies of submission. The use of this expression in the academic sphere goes hand in hand with a certain conceptualization of tierra adentro which has only recently begun to be addressed. This work supports the denaturalization of an expression that is commonly used but whose intrinsic meanings have not yet been properly defined or debated. Accordingly, it adds to the critical discussion regarding the use and theoretical scope of the vocabulary acquired from documentary sources for historical-anthropological research and it proposes some common aspects that could be applied to other spaces that were conceived as tierra adentro during the colonial experience.Fil: Lucaioli, Carina Paula. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Centro de Investigaciones Sociales. Instituto de Desarrollo Económico y Social. Centro de Investigaciones Sociales; Argentin

DEM simulations of initial deposition of colloidal particles around non-woven membrane spacers

The modelling of the initial deposition on membrane spacers of colloidal size particles immersed in a liquid is investigated using the Discrete Element Method (DEM) coupled to Computational Fluid Dynamics (CFD). The ability of this method to model surface interactions allows the modelling of aggregation and deposition at the particle scale. The numerical model adopts a mechanistic approach to represent the forces involved in colloidal suspension by including near wall drag retardation, surface interaction and Brownian forces. The model is implemented using commercially available software, so that results can be replicated in a standard and user-friendly framework. The effect of different spacer orientation with respect to feed direction is examined and results show that deposition of particles is increased around the spacer joints when feed orientation bisects the spacers' angle; when one of the spacer filaments is aligned with the feed inflow deposition occurs exclusively and uniformly on it. Simulation results demonstrate the validity of the method to describe the small-scale behaviour of micro-particles around spacers. The incipient fouling of particles in this size range is analogous to incipient bio-fouling of membrane spacers

Using the DEM-CFD method to predict Brownian particle deposition in a constricted tube

Modelling of the agglomeration and deposition on a constricted tube collector of colloidal size particles immersed in a liquid is investigated using the discrete element method (DEM). The ability of this method to represent surface interactions allows the simulation of agglomeration and deposition at the particle scale. The numerical model adopts a mechanistic approach to represent the forces involved in colloidal suspensions by including near-wall drag retardation, surface interaction and Brownian forces. The model is implemented using the commercially available DEM package EDEM 2.3®, so that results can be replicated in a standard and user-friendly framework. The effects of various particle-to-collector size ratios, inlet fluid flow-rates and particle concentrations are examined and it is found that deposition efficiency is strongly dependent on the inter-relation of these parameters. Particle deposition and re-suspension mechanisms have been identified and analyzed thanks to EDEM's post processing capability. One-way coupling with computational fluid dynamics (CFD) is considered and results are compared with a two-way coupling between EDEM 2.3® and FLUENT 12.1®. It is found that two-way coupling requires circa 500% more time than one-way coupling for similar results

13C Pyruvate Transport Across the Blood-Brain Barrier in Preclinical Hyperpolarised MRI.

Hyperpolarised MRI with Dynamic Nuclear Polarisation overcomes the fundamental thermodynamic limitations of conventional magnetic resonance, and is translating to human studies with several early-phase clinical trials in progress including early reports that demonstrate the utility of the technique to observe lactate production in human brain cancer patients. Owing to the fundamental coupling of metabolism and tissue function, metabolic neuroimaging with hyperpolarised [1-13C]pyruvate has the potential to be revolutionary in numerous neurological disorders (e.g. brain tumour, ischemic stroke, and multiple sclerosis). Through the use of [1-13C]pyruvate and ethyl-[1-13C]pyruvate in naïve brain, a rodent model of metastasis to the brain, or porcine brain subjected to mannitol osmotic shock, we show that pyruvate transport across the blood-brain barrier of anaesthetised animals is rate-limiting. We show through use of a well-characterised rat model of brain metastasis that the appearance of hyperpolarized [1-13C]lactate production corresponds to the point of blood-brain barrier breakdown in the disease. With the more lipophilic ethyl-[1-13C]pyruvate, we observe pyruvate production endogenously throughout the entire brain and lactate production only in the region of disease. In the in vivo porcine brain we show that mannitol shock permeabilises the blood-brain barrier sufficiently for a dramatic 90-fold increase in pyruvate transport and conversion to lactate in the brain, which is otherwise not resolvable. This suggests that earlier reports of whole-brain metabolism in anaesthetised animals may be confounded by partial volume effects and not informative enough for translational studies. Issues relating to pyruvate transport and partial volume effects must therefore be considered in pre-clinical studies investigating neuro-metabolism in anaesthetised animals, and we additionally note that these same techniques may provide a distinct biomarker of blood-brain barrier permeability in future studies