(376ak) Module-Scale Simulation of Hollow Fiber Vacuum Membrane Distillation Using Openfoam

Membrane distillation is a thermal process using a hydrophobic membrane as a physical barrier. MD processes are classified based on the phase condition in the distillate side. Vacuum membrane distillation (VMD) often provides higher distillate flux in comparison to direct contact membrane distillation (DCMD) and other types of MD processes. A VMD module consists of liquid feed, low-pressure gas, and porous membrane regions. In each phase, at least two transport phenomena are coupled. Momentum and heat transfer in the liquid feed side can be predicted using Navier-Stokes and Fourier equations, respectively. Through the membrane pores, migration of vapor molecules and heat transfer through the void and solid membrane regions can be explained using convective and diffusive heat transfer equations. In the low-quality vacuum phase of the distillate, a set of thermodynamic governing equations is necessary to adequately describe the momentum, heat, and mass transfer of the rare gas phase.
Due to the complexity of the multiple transport phenomena and their continuity at the two interfaces at the feed-side and distillate-side of the membrane, the performance modeling of VMD has been limited to a sample module system of one or several fibers. In reality, the number of hollow fibers in a cylindrical vessel ranges from (at least) a few hundred to thousands. In this case, the distillate flux is sensitively influenced by the configuration of hollow fibers, aligned in parallel. Even distribution of feed flow to each hollow fiber is a challenging task, and therefore the performance of the VMD process is highly dependent on geometrical configurations of packed hollow fibers and flow patterns. In this vein, the current paper investigates the VMD module of real size, having hollow fibers of an order of 100, and simulate the coupled transport of momentum, heat, and mass in a seamlessly combined manner. An open-source CFD package, OpenFOAM is used mainly to solve for the thermal fluid and gas, and specific solver for MD is developed to investigate the coupled transport phenomena without theoretical approximations.