Design for Cascade of Crossflow Direct Contact Membrane Distillation

TLDR: In this article, a shortcut design method is presented to determine the number of identical crossflow modules needed to extract maximum heat recovery between an inlet and exit brine temperature, which is dependent on two observations: (1) existence of a unique relationship between temperature drop across a stage and the temperature of closest approach between brine and distillate streams at the top of the stage, which defines an operating line; (2) ΔTend remains relatively constant from stage to stage.

Abstract: The use of crossflow direct contact membrane distillation (XF-DCMD) modules allows lower velocities and volumetric flows on the brine side while still maintaining good heat-transfer coefficients. The key to using these modules in energy-efficient processes requires that the heat be recovered from the hot distillate exit stream with close temperatures of approach. This is best accomplished in a cascade of crossflow modules arranged in a manner approaching the behavior of countercurrent DCMD modules. A short-cut design method is presented to determine the number of such identical modules needed to extract maximum heat recovery between an inlet and exit brine temperature. This method is dependent on two observations:  (1) existence of a unique relationship between brine temperature drop across a stage (ΔTstage) and the temperature of closest approach between brine and distillate streams at the top of the stage (ΔTend), which defines an operating line; (2) ΔTend remains relatively constant from stage to stage...