Abstract
In electro-membrane processes, a pressure difference may arise between solutions flowing in alternate channels. This transmembrane pressure (TMP) causes a deformation of the membranes and of the fluid compartments. This, in turn, affects pressure losses and mass transfer rates with respect to undeformed conditions and may result in uneven flow rate and mass flux distributions. These phenomena were analyzed here for round pillar-type profiled membranes by integrated mechanical and fluid dynamics simulations. The analysis involved three steps: (1) A conservatively large value of TMP was imposed, and mechanical simulations were performed to identify the geometry with the minimum pillar density still able to withstand this TMP without collapsing (i.e., without exhibiting contacts between opposite membranes); (2) the geometry thus identified was subject to expansion and compression conditions in a TMP interval including the values expected in practical applications, and for each TMP, the corresponding deformed configuration was predicted; and (3) for each computed deformed configuration, flow and mass transfer were predicted by computational fluid dynamics. Membrane deformation was found to have important effects; friction and mass transfer coefficients generally increased in compressed channels and decreased in expanded channels, while a more complex behavior was obtained for mass transfer coefficients.
Highlights
In electro-membrane processes such as electrodialysis (ED) [1] and reverse electrodialysis (RED) [2], performance predictions are usually based on simulation models or empirical correlations in which the geometric configurations of the solution-filled channels and of the ion exchange membranes are assumed to be the nominal one [3,4,5].since ion exchange membranes are usually thin (~102 μm) and have a low stiffness (Young modulus 101 –103 MPa), they may undergo significant deformations if even small transmembrane pressures (TMP) of the order of 10−1 bar are applied
Time-dependent considered as a possible means to improve process performances in the “breathing cell” concept for membrane deformation has recently been considered as a possible means to improve process reverse electrodialysis systems [13]
In a recent paper [20], we presented integrated mechanical and fluid dynamics simulations of electro-membrane system representative of electrodialysis or reverse electrodialysis, aimed at assessing an electro-membrane system representative of electrodialysis or reverse electrodialysis, aimed at the influence of transmembrane pressures on membrane/channel deformation and on pressure assessing the influence of transmembrane pressures on membrane/channel deformation and on drop and mass transfer
Summary
Since ion exchange membranes are usually thin (~102 μm) and have a low stiffness (Young modulus 101 –103 MPa), they may undergo significant deformations if even small transmembrane pressures (TMP) of the order of 10−1 bar are applied. Such values of TMP commonly arise in real stacks due to different frictional pressure drops in the two channels or to other causes, depending on the flow arrangement selected (e.g., parallel flow yields the lowest TMP and counter flow the highest). Fluid–structure interactions and its effects are still few, especially for electro-membrane processes such experiments, models, and simulations concerning fluid–structure interactions and its effects are still as ED and RED
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