Validation and Analysis of Forward Osmosis CFD Model in Complex 3D Geometries

Abstract

In forward osmosis (FO), an osmotic pressure gradient generated across a semi-permeable membrane is used to generate water transport from a dilute feed solution into a concentrated draw solution. This principle has shown great promise in the areas of water purification, wastewater treatment, seawater desalination and power generation. To ease optimization and increase understanding of membrane systems, it is desirable to have a comprehensive model that allows for easy investigation of all the major parameters in the separation process. Here we present experimental validation of a computational fluid dynamics (CFD) model developed to simulate FO experiments with asymmetric membranes. Simulations are compared with experimental results obtained from using two distinctly different complex three-dimensional membrane chambers. It is found that the CFD model accurately describes the solute separation process and water permeation through membranes under various flow conditions. It is furthermore demonstrated how the CFD model can be used to optimize membrane geometry in such as way as to promote the mass transfer.

Open-source CFD model for optimization of forward osmosis and reverse osmosis membrane modules

“…In our original CFD model [21,23] the solver used a PISO algorithm [33] to couple the continuity and Navier-Stokes equations in a transient manner. This implementation allowed the user to converge a single simulation of a full lab-scale membrane module (on a personal computer with 8 CPUs) within of 1-2 weeks [23] -however for geometry optimization where hundreds of different geometries must be tested, such long convergence times are untractable.…”

“…In this model, we used a generally accepted analytical equation for membranes in FO systems that parameterizes ICP in terms of a single membrane structural parameter [22], solving this implicit analytical equation numerically for each face in the mesh at each timestep. We first verified our model against similar CFD models for pressure-driven systems [21] and later validated the model against experimental data, showing it capable of reproducing experimental FO observations [23].…”

“…ANSYS-CFX [11,26,30] or COMSOL [31]. In this work, we use an open source numerical framework and we have made the CFD model (solver and boundary conditions for FO and RO membranes) publicly available together with this publication [32].…”

Pore-scale modeling and simulation of flow, transport, and adsorptive or osmotic effects in membranes: the influence of membrane microstructure

“…This contrasts with the majority of theoretical studies which are performed at the Darcy scale (see, for example, [9, 12,26] for forward osmosis (FO) applications and [6,17,28] for reactive transport). A detailed porescale description of the processes yields more accurate results than a Darcy scale description, but at a higher computational cost.…”

“…In contrast, there is a two-way coupling between the Navier-Stokes-Brinkman and the convectiondiffusion systems of equations for the FO experiment, due to the dependence of the interfacial conditions (12) and (13) on the velocity, pressure and solute concentration. In general, the algorithms discussed here are developed to allow an investigation of two cases: (i) the temporal evolution of the concentration, the velocity and the pressure fields, and (ii) the spatial distributions of the solute concentration, pressure and velocity at steady state.…”