Hollow fiber geometry

Membrane systems consist of membrane elements or modules. For potable water treatment, NF and RO membrane modules are commonly fabricated in a spiral configuration. An important consideration of spiral elements is the design of the feed spacer, which promotes turbulence to reduce fouling. MF and UF membranes often use a hollow fiber geometry. This geometry does not require extensive pretreatment because the fibers can be periodically backwashed. Flow in these hollow fiber systems can be either from the inner lumen of the membrane fiber to the outside (inside-out flow) or from the outside to the inside of the fibers (outside-in flow). Tubular NF membranes are now just entering the marketplace. 

Wickramasinghe S.R., Semmens J., and Cussler E.L., Mass transfer in various hollow fiber geometries, J. Membr. Sci. 69, 235, 1992. 

The hollow-fiber geometry is preferred for CCRO because it is more convenient to provide circulation on both sides of fibers than it is for flat-sheet membranes. A number of hollow-fiber NS-lOO membrane modules were tested at 250 psi. The fibers were stable for several days at this operating pressure at feed concentrations up to 25 volZ ethanol. However, higher operating pressure and/or feed concentration caused these membranes to fail rapidly due to plasticization weakening of the polysulfone support. The CTA... 

The low ethanol rejection and the instability of the hollow-fiber NS-100 membranes preclude the use of this membrane for practical ethanol enrichment. Nevertheless, for the purpose of demonstrating the concept of CCRO using hollow-fiber membranes, CCRO experiments were conducted at the reduced ethanol concentration of 10 vol%. The permeate fluxes of NS-100 modules were measured at 250 psi in the absence and presence of recirculation with a 10-volX ethanol solution. The results were varied recirculation brought about flux increases ranging from 5% to about 20%. The limited flux increase may again be explained in terms of the formation of a polyamine gel during NS-100 membrane fabrication. Nevertheless, the flux increase shows that the hollow-fiber geometry is a viable one for CCRO operation. 

Alternate Hollow Fiber Geometries, Hollow Fiber Fabric,... 

Supported Liquid Membranes. A SLM can be fabricated in at least three different geometries. Planar or flat sheet SLMs are very useful for laboratory research and development purposes, but the surface area to volume ratio of flat sheets is too low for industrial applications. Spiral wound and hollow fiber geometries can... 

Membrane Physical Structure The physical structure of the hollow-fiber membrane in Toyobo RO modules is optimized to provide mechanical strength resistance to collapse in a hydrostatic pressure environment. This is achieved by spinning the hollow-fiber geometry at dimensions consistent with the mechanics of a tiny hollow tube or pipe and the material properties of a strong CTA polymer. 

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