(222e) Mass Transfer in Crimped Hollow Fiber Membrane Modules

Membranes in the form of fine hollow fibers are used to perform a wide range of separations from hemodialysis to dehydration. The fibers commonly are fabricated into large bundles or modules for use in a separation process to facilitate handling and scale-up.

Module performance depends strongly on membrane transport properties but other factors may be equally important including concentration and thermal boundary layers adjacent to the fiber surface as well as uniformity of flow through the module.

As demonstrated by Professor Cussler's group, the introduction of a cross-flow component to the shell flow through the module can reduce the impact of shell concentration boundary layers. This can be done by placing baffles within the fiber bundle or other bundle structural features. Alternatively, one may crimp the fiber. Crimping transforms straight fiber into wavy fiber much like a permanent creates curly hair.

Fiber bundles manufactured from crimped fiber intrinsically introduce a cross-flow component in the shell as fluid flows through it. The effect of crimping on shell side mass transfer coefficients is reported here. Experimental measurements using commercial hemodialyzers indicate crimping can increase shell mass transfer coefficients dramatically. Simulations of mass transfer are compared to experimental measurements and used to evaluate theoretically the effect of crimp length.