Permeate Flux Curve Characteristics Analysis of Cross-Flow Vacuum Membrane Distillation

In this Article, the heat and mass transfer processes were analyzed to build a mathematic model of cross-flow vacuum membrane distillation (VMD) for deriving the theoretical relationship of permeate flux with operation conditions and better understanding of the novel VMD performance. The common characteristics of permeate flux curves were studied experimentally under different operation conditions in cross-flow VMD. Three main operation conditions (feed inlet temperature, vacuum level, and feed velocity) affect the permeate flux curves with different mechanisms, which form different types of permeate flux curves. Feed inlet temperature mainly affects saturated vapor pressure of feed at membrane surface, and the characteristic of the curves of permeate flux versus feed inlet temperature is opening up incremental parabola. Vacuum level mainly affects the vapor pressure of permeate side, and the characteristic of the curves of permeate flux versus vacuum level of permeate side is the linear growth line. Feed velocity mainly affects residence time of feed in membrane module and convective heat transfer coefficient of boundary layer in feed side, and the characteristic of the curves of permeate flux versus feed velocity is right opening growth parabola. Temperature polarization on the feed side intensifies with the increase of permeate flux under any operation condition, and even with the increases of feed inlet temperature, vacuum level of permeate side, and feed velocity.