Designing Better Membrane Modules Using CFD

Abstract

Abstract In the last decades, a large number of studies have been carried out on the utilization of membranes in separation processes. However, most of these studies deal with material properties, experimental investigations and process modeling. Only quite a few authors utilized computational fluid dynamics (CFD) to analyze the flow and mass transfer in membrane modules. Using CFD it is possible to obtain spatially resolved information on the behavior of membrane modules, allowing for the investigation of geometric effects on the performance of the module. This includes e. g. the positioning of the permeate outlets, the flow alignment (co- and/or counter-current), the use of spacers and other mixing promoters and also the subject of concentration polarization close to the membrane surface. In our present study we made use of OpenFOAM®, which is a free open sourced CFD toolbox. The toolbox enables for introducing new solver code, membraneFoam, based on the standard multicomponent solver reactingFoam. In membraneFoam suitable source and sink terms have been added to account for trans-membrane flux – in this case based on the solution-diffusion model for glassy polymer gas permeation membranes. The solver has been preliminary validated using literature data obtained from a process simulation code. In a first stage of the research work the positioning of the permeate outlet and the flow alignment have been investigated for a hollow fiber gas permeation module. By adjusting the position of the permeate outlet the shell side flow can be co-current, counter-current or mixed type relative to the retentate flow inside the fibers. Since this influences the driving force for the trans-membrane flux, effects on the module performance are expected which have been analyzed using the described membraneFoam CFD approach.