(659a) Static Mixing Spacers for Spiral Wound Modules

Membranes play a critical role in many separation processes ranging from nitrogen production to desalination. The membranes are used most commonly in the form of fine hollow fibers or sheets. The sheet form is used to produce spiral wound modules that permit the efficient contacting of process streams with the membrane in a compact form.

Spiral wound modules are the dominant form used in reverse osmosis and nanofiltration membrane processes. Spacers are used in spiral wound modules to create feed and permeate flow channels and to enhance mass transfer rates by reducing concentration polarization. Most spacers possess a ladder or mesh structure and rely on the generation of turbulence and eddies to enhance mass transfer. The literature contains numerous experimental and theoretical studies of how pressure drop and mass transfer rates depend on the geometry of these spacers.

Spacer design features that increase mass transfer rates also tend to increase pressure drop. The preferred spacer is determined by the tradeoff between the reduction in membrane area and concomitant increase in pumping costs. A review of previous spacer design studies is presented with emphasis on the proper basis for comparison of the results.

Following this review, we present a new spacer paradigm. The spacer acts as a static mixer for planar flow channels and mixes without generating turbulence and eddies. Simulations of flow and mass transfer with the new spacer were performed using computational fluid dynamics. The results indicate mass transfer rates are greater than that reported for other spacer designs. Flow visualizations clearly show how the spacer mixes fluid.