Framework for coupled simulation of electrodialysis processes

  • Konzept und Umgebung für gekoppelte Simulationen von Elektrodialyse-Prozessen

Masilamani, Kannan; Roller, Sabine (Thesis advisor); Marquardt, Wolfgang (Thesis advisor)

1st edition. - Siegen : universi - Universitätsverlag Siegen (2021)
Book, Dissertation / PhD Thesis

In: Simulation techniques in Siegen - STS 4
Page(s)/Article-Nr.: 1 Online-Ressource : Illustrationen, Diagramme

Dissertation, RWTH Aachen University, 2020

Abstract

Electrodialysis is an efficient process for seawater desalination that involves various interacting phenomena. In this process, ions are transported by flow, diffusion and an electric force and separated by selective membranes. For the optimization of this process, it is important to understand these interactions. This work presents rigorous mathematical models to describe the overall process and develops a numerical strategy for its simulation. With this approach it becomes possible to simulate the involved physical effects and their interactions in detail. To achieve this, the Maxwell-Stefan equations for mixtures are used. They take into account the electrical force and the multicomponent interactions with concentration dependent diffusivity coefficients and thermodynamic factors. Additionally, the usual assumption of local electroneutrality is not assumed to allow the nonideal effects in the electrical double layer near the membrane. For the numerical solution of these equations, the multicomponent lattice Boltzmann method (LBM) is developed and implemented in the solver Musubi. This model for the channel flow is coupled with an electric field and a model for the membranes. To obtain the electric field, the LBM that solves the Poisson’s equation is implemented in Musubi. The channels between the membranes are realized by spacers with complex geometry. A mesh generator (Seeder) on the basis of octrees is developed to ensure the appropriate discretization of the mesh for these channels. An essential part of this work is dedicated to the development of the parallel scaling coupling tool APESmate. APESmate is developed within the APES suite along with Seeder and Musubi on a central octree data structure that allows efficient handing of I/O on large scale distributed parallel computing systems.The developed software is used to compare the nonideal multicomponent model for various concentrations and surface potentials. The results show that nonideal effects increase with the concentration, especially in the electrical double layer. The spacers for various hydrodynamic angles and inflow velocities near and away from a sealed corner are investigated to find the design with reduced pressure drop and without low velocity zones. The highly resolved simulations show that the pressure drop increases with the hydrodynamic angle, while the extend of the low flow regions decreases.

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