(371a) Direct Numerical Simulations of Polarization Phenomena in Direct Contact Membrane Distillation

Direct contact membrane distillation (DCMD) is a relatively new thermal-driven membrane separation technology. In a DCMD system, warm feed and cool permeate flow on opposite sides of a hydrophobic membrane. The temperature difference causes water vapor to evaporate from the feed and condense in the permeate. To date, computational fluid dynamics (CFD) studies of DCMD focus primarily on the challenge of temperature polarization. For treating high concentration brines, however, concentration polarization is another major challenge that reduces system efficiency and leads to mineral scaling. Consequently, we perform a CFD study of DCMD systems, with a focus on applications to treating high concentration brines rejected by reverse osmosis systems.

We develop a dedicated in-house CFD method to simulate 3-D, unsteady, heat and mass transport within plate-and-frame DCMD systems. The coupled momentum, energy, and mass transport equations are discretized spatially using finite-volume methods. The equations are integrated in time using an efficient, non-iterative, semi-implicit projection method to solve for the pressure field in the Navier-Stokes equations. We present the results of a parametric study of 3-D temperature and concentration polarization under a variety of operating conditions, including feed and permeate flow rates and temperatures, feed concentration, and membrane properties. The numerical results are benchmarked with a parallel experimental study of permeate flux and thermal efficiency.