CFD-assisted thin channel membrane characterization module design

Abstract

This project involved the design of a thin channel cross-flow module for the characterization of flat ceramic membranes. A primary objective of this work was to ensure that the flow characteristics over the permeating area were uniform. To house these membranes, a thin channel module with a long rectangular base was envisioned. The module feed is supplied by a multi-inlet tube-type plenum meant to provide a uniform flow distribution through pressure equilibration attained in its volume. The design criteria for the module were minimization of both the flow non-uniformity and the pressure drop across the permeating area which was a central rectangular portion of a larger slab-style cell. The flow non-uniformity was taken as the normalized standard deviation of the velocity field above the permeating area. The pressure drops considered were those across the inlet plenum and across the permeating area normalized with respect to the outlet pressure. The computational fluid dynamics (CFD) scheme which calculated the above module characteristics was a k- ε based turbulent transport model which used the finite difference method. Design variables considered were: the plenum diameter, module width, height and length, and the diameters, distribution and number of the inlets on the plenum. The distribution of the inlet diameters was determined by two variables: either a linear or parabolic profile of variable slope and model coefficient. The operating variables were the cross-flow velocity and the plenum inlet pressure. A two-level factorial design was used to screen the design variables. A refined three-level factorial design was used with a reduced set of design variables to optimize the module and study the response surface. The final module design parameters were chosen such that the design criteria of flow uniformity and low pressure drop were met under a preset range of operating conditions. The local gradients of the response surface were used to verify that the design criteria were not overly sensitive to the selected module design parameters.