Impact of gas bubbling on wetting control in a submerged membrane distillation
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13th Minisymposium Chemical & Process Engineering
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Membrane wetting is an inherited phenomenon in membrane distillation (MD) processes, which considerably reduces the separation efficiency. However, the wetting phenomenon in MD is not well-understood and yet little work has been done in this area. Recently, attention has been devoted in reducing membrane pore wetting by modifying membrane surface chemistry and geometry , whereas controlling membrane wetting by preventing adsorption equilibrium of the wetting agent at the feed/membrane interface has not been studied for MD systems . The latter can be achieved by swapping liquid which partly tends to penetrate the macro porous membrane structure with gas bubbles. Therefore, based on the surface renewal theory , the wetting agents do not have time to accumulate on the macro porous structures, because the interface is displaced or swept from the system by the gas bubbles (Figure 1). This work studies a novel approach, gas-bubbling membrane distillation (GBMD) for preventing wetting incident by introducing air bubbles in the feed stream. Both effects of flow pattern and flow regime on the performance of GBMD process in terms of permeate flux and wetting rate in this process are studied. The results shows that the performance of MD is enhanced evidently by air-bubbling method, specially for low surface tension solutions. The flux is almost doubled at certain feed velocity and gas/ liquid ratio. In addition, the study shows that flow pattern is the key factor affecting wetting occurrence in MD. It is found that the wetting rate in slug flow is much lower than that in the bubbly flow and permeate flux of slug flow is higher than that of the bubbly flow.