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The improvement of feed spacers with optimal geometry remains a key challenge for spiral-wound membrane systems in water treatment due to their impact on the hydrodynamic performance and fouling development. In this work, novel spacer designs are proposed by intrinsically modifying cylindrical filaments through perforations. Three symmetric perforated spacers (1-Hole, 2-Hole, and 3-Hole) were in-house 3D-printed and experimentally evaluated in terms of permeate flux, feed channel pressure drop and membrane fouling. Spacer performance is characterized and compared with standard no perforated (0-Hole) design under constant feed pressure and constant feed flow rate. Perforations in the spacer filaments resulted in significantly lowering the net pressure drop across the spacer filled channel. The 3-Hole spacer was found to have the lowest pressure drop (50%-61%) compared to 0-Hole spacer for various average flow velocities. Regarding permeate flux production, the 0-Hole spacer produced 5.7 L m.h and 6.6 L m.h steady state flux for constant pressure and constant feed flow rate, respectively. The 1-Hole spacer was found to be the most efficient among the perforated spacers with 75% and 23% increase in permeate production at constant pressure and constant feed flow, respectively. Furthermore, membrane surface of 1-Hole spacer was found to be cleanest in terms of fouling, contributing to maintain higher permeate flux production. Hydrodynamic understanding of these perforated spacers is also quantified by performing Direct Numerical Simulation (DNS). The performance enhancement of these perforated spacers is attributed to the formation of micro-jets in the spacer cell that aided in producing enough unsteadiness/turbulence to clean the membrane surface and mitigate fouling phenomena. In the case of 1-Hole spacer, the unsteadiness intensity at the outlet of micro-jets and the shear stress fluctuations created inside the cells are higher than those observed with other perforated spacers, resulting in the cleanest membrane surface.

Acoustic droplet vaporization is investigated in a theoretical model. This work is motivated by gas embolotherapy, a developmental cancer treatment involving tumor infarction with gas microbubbles that are selectively formed from liquid droplets. The results indicate that there exists a threshold value for initial droplet size below which the bubble evolution is oscillatory and above which it is smooth and asymptotic, and show that the vaporization process affects the subsequent microbubble expansion. Dampening of the bubble expansion is observed for higher viscosity and surface tension, with effects more pronounced for droplet size less than 6 m in radius. © 2010 American Institute of Physics. ͓doi:10.1063/1.3376763͔Gas embolotherapy ͑GE͒ refers to intended occlusion of the blood flow in the vasculature by means of gas bubbles. 1,2The envisioned therapeutic application for GE is the treatment of cancer by occluding blood flow to tumors and for localized drug delivery. The process of GE involves the injection of superheated dodecafluoropentane ͑DDFP, C 5 F 12 ͒ droplets, each encapsulated in an albumin or lipid shell, into the blood stream. The blood flow carries these droplets into the tumor microcirculation where high-intensity ultrasound is used to initiate acoustic droplet vaporization ͑ADV͒ to form bubbles near the desired occlusion sites.Some important issues regarding the implementation of GE to the clinical setting were pointed out by Bull.2 One of these issues is to understand the dynamics of ADV and the stresses ADV induces on the vessel wall. High wall stresses can lead to a range of bioeffects, including vessel rupture and changes in vessel permeability, which could deleterious or advantageous depending on the treatment strategy and the severity of the bioeffects. Thus, a thorough understanding of the ADV process is needed in translating this treatment modality to the clinic.Recent in vitro experiments 3-5 that were focused from a radiological perspective indicate that when the ultrasound beam hits the superheated DDFP microdroplets, a nucleation site is formed. This nucleation site located inside the droplet triggers the vaporization event. Similar experimental observations were reported by Shepherd and Sturtevant 6 for large superheated butane droplets with the difference that the phase change initiation was achieved by direct heating. Related work by Farhat et al.7 investigated a cavitation bubble inside a water droplet in microgravity. The cavitation was achieved using a spark discharge, a toroidal collapse via a jet formation was observed. A modified Rayleigh-Plesset theory was utilized to explain the bubble collapse mechanism. The only models of bubble expansion in ADV were presented by Ye and Bull,8,9 where direct numerical simulations were carried out for the expanding bubble inside rigid and flexible tubes. Important trends of pressure, velocity, and stress distribution in rigid and flexible tubes were revealed by this study.In the present work, we propose an ADV model for bubble evolution f...

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