Avaliação dos efeitos fluidodinâmicos em módulos de membranas plana, curva e espiral via CFD.

Abstract

The membrane separation processes have several applications in the most diverse sectors of the industry, standing out the desalination by reverse osmosis (RO) for the production of drinking water from brackish and / or sea water, using as driving force the transmembrane pressure in a semipermeable membrane. This work had the aim to study the fluid dynamics effects in a spiral membrane module. A mathematical model was developed for the separation process, adopting the solution diffusion model based on the equations of conservation of the mass, amount of movement and of the chemical species. For this study was used the commercial package Ansys CFX® 15.0. The model was applied to a flat membrane module in two and three dimensions where the numerical results had a good agreement with the results of studies reported in the specific literature. A mesh quality study was carried out using the Grid Convergence Index (GCI) to analyze the independence of the numerical results with the mesh used. Three process variables were studied: feed velocity, transmembrane pressure and initial concentration of the solution of NaCl. The model was applied to different curvatures of the membrane module indicated an improvement in membrane performance with the intensification of the curvature of the module. The configuration of the spiral membrane showed a relevant increase in the production capacity of the membrane module. The permeate mass flow depended on the initial NaCl concentration, transmembrane pressure and the number of turns of the membrane. The results showed that variations in the quantities involved in the separation process, as velocity, initial concentration and transmembrane pressure, influence the development of the layer of polarization concentration, as well as the permeate flux. The increase of the feeding velocity and reduction of the initial concentration favor the reduction of the polarized layer, and the increase of the transmembrane pressure elevates the permeate flow. The results of the simulations showed a good representation of the transfer phenomena involved in the desalination process.