458491 Theoretical Analysis of Enhanced Mass Transfer in Modules with Novel Twisted Hollow Fiber Membrane

Monday, November 14, 2016: 12:35 PM
Plaza A (Hilton San Francisco Union Square)
Andrew Zydney1, Ali Borhan1, Seyed Pouria Motevalian1 and Hongyi Zhou2, (1)Chemical Engineering, The Pennsylvania State University, University Park, PA, (2)Membrane and Separations Technology, GE Global Research, Niskayuna, NY

A number of approaches have been used to develop membrane modules with enhanced mass transfer. Rotating membrane systems generate Taylor vortices that can significantly increase flux and reduce fouling, but these modules have very low membrane packing densities (membrane area per unit volume) and are very difficult to scale-up. Helically wrapped hollow fibers generate Dean vortices in a much more scalable geometry, although these modules have not yet been commercialized for large-scale applications. The objective of this work was to examine the behavior of twisted hollow fiber modules in which Dean vortices are generated by the coiled flow that occurs within a twisted elliptical flow channel. Computational fluid dynamic simulations are used to examine incompressible flow through twisted elliptical and helically-coiled cylindrical fibers for typical flow Reynolds numbers employed in membrane filtration processes (Re < 200). The resulting flow fields are compared in terms of the distributions of vorticity and wall shear rate, the pressure drop, and the azimuthally-averaged normal velocity in the vicinity of the wall. The secondary flow in twisted elliptical fibers generates significant recirculation flow leading to near-wall velocities directed normal to the surface of the membrane (below figure). The azimuthally-averaged normal velocity near the wall of a twisted elliptical fiber is found to be two to four orders of magnitude larger than typical ultrafiltration velocities. For Re < 75, the average wall shear rate and normal velocity near the wall are found to be significantly higher in twisted elliptical fibers compared to their helical counterparts. Modules produced using twisted elliptical hollow fibers would be linearly scalable by changing the number of parallel fibers, without any alteration in the device hydrodynamics. These findings highlight the potential for mass transfer and flux enhancement using modules with novel twisted elliptical hollow fiber membranes.

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See more of this Session: Honorary Session for Georges Belfort I
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