Model-guided design of high-performance membrane distillation modules for water desalination

The significance of geometrical and physical parameters of hollow fiber membrane modules in the membrane distillation process has not been fully evaluated. In this study, we develop a three-dimensional multi-physics model of a hollow fiber membrane module in order to investigate the effect of operating and design parameters on the module performance. The permeate flux and thermal efficiency of the system are considered as the characteristic parameters of the module, operated in direct contact membrane distillation mode (DCMD). The simulation results indicate that the permeate flux for the module can be enhanced by 54% when 1) the hollow fibers are in close-packed configuration, and 2) the interspacing parameter, the ratio of a fiber radius to the center-to-center distance between neighboring fibers, is adjusted properly. We identify the fiber interspacing parameter as a critical parameter for the module design. The permeate flux significantly drops when the interspacing parameter is equal to a value of 0.5, implying that the fibers are adjacent to each other. Moreover, the results indicate that, in our system, the time constant for the mass transfer process through the membrane is higher than that of heat transfer, meaning that the DCMD process for a hollow fiber membrane module under parallel flow condition is a mass transfer limited process.