Yang, Xing, Fridjonsson, E. O, Johns, M. L, Guan, Guoqiang, Wang, Rong and Fane, Anthony G (2013) Flow enhancement strategies and hydrodynamic analysis in hollow fiber modules for membrane distillation applications. In: International Desalination Association World Congress on Desalination and Water Reuse, 10-25 Oct 2013, Tianjin, China. (Unpublished)

Abstract

Low-field bench-top nuclear magnetic resonance imaging (MRI) has been applied to investigate the hydrodynamics and flow distributions in novel hollow fiber modules designed for the membrane distillation (MD) process. For this purpose, pulse field gradient (PFG) technique was applied to acquire fluid displacement probability distribution (propagator) information inside the module. Velocity was mapped using a combined MRI and PFG method. As an extension of our prior MD module study, the flow dynamics and module performance of four representative configurations (i.e., with randomly-packed fibers, spacer-knitted fibers, curly and semi-curly fibers) were investigated in terms of the cross-section imaging, diffusion and propagator experiments, and velocity maps in the shell-side flow. The results showed that compared to the randomly-packed module (as a benchmark), the configuration with curly fibers had narrower propagators in the bulk flow direction, a higher probability of water molecules with large displacement in the Y (parallel-to-flow) direction, and more intense local mixing and flow homogeneity were revealed through the standard deviation calculation, which corresponded well to the enhanced MD performance. On the contrary, as a well-performed configuration evaluated in membrane process tests, the module with spacer-knitted fibers showed interesting ―channeling‖ phenomena via NMR velocity imaging at a relatively high flow rate. Fortunately, the propagators were able to provide more comprehensive information to understand the unusual flow behaviors in such complex channel.

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