P.R. Brito-Parada

Polydispersed flow modelling using population balances in an adaptive mesh finite element framework

Abstract An open-source finite element framework to model multiphase polydispersed flows is presented in this work. The Eulerian–Eulerian method was coupled to a population balance equation and solved using a highly-parallelised finite element code—Fluidity. The population balance equation was solved using DQMOM. A hybrid finite element–control volume method for solving the coupled system of equations was established. To enhance the efficiency of this solver, fully-unstructured non-homogeneous anisotropic mesh adaptivity was applied to systematically adapt the mesh based on the underlying physics of the problem. This is the first time mesh adaptivity has been applied to the external coordinates of the population balance equation for modelling polydispersed flows. Rigorous model verification and benchmarking were also performed to demonstrate the accuracy of this implementation. This finite element framework provides an efficient alternative to model polydispersed flow problems over the other available finite volume CFD packages.

CFD study of liquid drainage in flotation foams

Abstract Froth flotation is a separation process used in a number of applications worldwide. Recycled paper deinking, water purification, bitumen recovery from oil sands and, in particular, mineral separation, benefit from this industrial operation. The complex phenomena occurring within the froth phase of a flotation cell, however, are not entirely understood. The flow patterns of the froth, the drainage of liquid within the system and the behaviour of solid particles, represent a challenge for both experimental and numerical studies. State of the art Computational Fluid Dynamics (CFD) techniques can be used to assess the performance of flotation tanks in order to achieve better equipment design and enhanced operations. This work makes use of mathematical models for foam flow and liquid drainage in two-phase foams implemented in Fluidity, a finite element code which incorporates anisotropic adaptive remeshing. Adaptivity is an important feature for improving the computational cost of modelling these systems, as there are boundary layers present in the process whose size is independent of the scale of the flotation tank being modelled. Potential flow theory, previously shown to adequately represent the flow of froths in flotation tanks, has been used to obtain the velocity and trajectory of the foam, whilst the equations for liquid drainage in foams have been extended to consider transient simulations in up to three dimensions. In addition, the flexibility offered by the Finite Element Method in terms of the selection of the element types has been exploited, and mixed elements are employed to accurately represent the fields of interest. This work presents results from numerical investigations of a large laboratory scale flotation tank and discusses important aspects of the model that make it suitable for studying industrial processes involving the drainage of liquid through flowing foams.

The influence of design parameters on the separation of biomass in mini-hydrocyclones

Abstract Small hydrocyclones are an attractive technology for biomass separation from fermentation processes. The interactive effect of design parameters on the performance of mini‐hydrocyclones is, however, not fully explored and studies are often limited by the challenges in manufacturing such small units. Here, 10‐mm mini‐hydrocyclones are produced by 3D printing and the impact of spigot diameter, vortex finder diameter and height on separation performance is studied. A central composite rotatable design was adopted to obtain information on the relation between the variables and their influence on concentration ratio and recovery of yeast from a highly diluted system. A Pareto front for separation performance was generated and shown to be suitable to select an optimal design for a set of process constraints.

A multi-criteria decision framework for the selection of biomass separation equipment

Abstract For the first time, a two‐stage decision support framework for equipment selection, applied to biomass separation, is presented. In the first stage, the framework evaluates from a number of equipment based on the process requirements and outputs only those that offer a technically feasible separation. In the second stage, the analytic hierarchy process is applied for performing a multicriteria decision analysis to select amongst the feasible equipment based on separation performance and energy consumption criteria. This approach systematically considers the relative importance of those different alternatives and selection criteria by pairwise comparisons. The output of the framework is an overall ranking of equipment as well as a sensitivity analysis of the results for different weighting of the criteria. These results can be used to equip practitioners in the field of bioseparations with a tool for making more consistent and better‐informed equipment selection decisions.

Geometry and Topology of Two-Dimensional Dry Foams: Computer Simulation and Experimental Characterization

Pseudo-two-dimensional (2D) foams are commonly used in foam studies as it is experimentally easier to measure the bubble size distribution and other geometric and topological properties of these foams than it is for a 3D foam. Despite the widespread use of 2D foams in both simulation and experimental studies, many important geometric and topological relationships are still not well understood. Film size, for example, is a key parameter in the stability of bubbles and the overall structure of foams. The relationship between the size distribution of the films in a foam and that of the bubbles themselves is thus a key relationship in the modeling and simulation of unstable foams. This work uses structural simulation from Surface Evolver to statistically analyze this relationship and to ultimately formulate a relationship for the film size in 2D foams that is shown to be valid across a wide range of different bubble polydispersities. These results and other topological features are then validated using digital image analysis of experimental pseudo-2D foams produced in a vertical Hele-Shaw cell, which contains a monolayer of bubbles between two plates. From both the experimental and computational results, it is shown that there is a distribution of sizes that a film can adopt and that this distribution is very strongly dependent on the sizes of the two bubbles to which the film is attached, especially the smaller one, but that it is virtually independent of the underlying polydispersity of the foam.