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Understanding of the liquid overflow behavior inside micro-structured falling film reactors based on a wetting approach

Abstract : This study investigates the behavior of gravity-driven liquid films inside falling film micro-reactors and focuses on the conditions necessary to obtain and break-up the complete liquid overflow from all of the channels. Micro-structured falling film reactors containing 6-10 straight parallel rectangular microchannels were designed, constructed and tested. The main objective was to show experimentally the influence of liquid wettability on the hydrodynamic behavior. To achieve this, we explored the fluidic motion as a function of several parameters, including micro channel size, the structural materials of the reactor (stainless steel, fluorocarbon and silicon oxide), liquid nature (water, water ethanol mixtures and aqueous solutions of a ionic sodium dodecyl sulfate surfactant) and concentration levels. The major parameters that control the hydrodynamic behavior are the liquid/solid advancing and receding contact angles. The advancing contact angle governs the filling and the overflow of the channels, while the receding contact angle drives the characteristics of the break-up of the total overflow. Through experimentation, we identified a relationship between the contact angles and the resulting liquid flow patterns. We observed that spreading increases with higher ethanol content levels, surfactant concentration or by using a silicon oxide reactor. The flow rate required to achieve or break-up the total overflow decreased as a result. Finally, all of these results can be summarized by two master curves relating the critical flow rates to achieve and break-up the overflow with the advancing and receding contact angles, respectively. The channel dimensions also play a role in the hydrodynamic behavior, since the reduction of the channel width and distance between successive channels leads to a decrease in the critical flow rates.
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Thibault Roques-Carmes, Hadj Semara, Cedric Guyon, Michael Tatoulian, Stephanie Ognier, et al.. Understanding of the liquid overflow behavior inside micro-structured falling film reactors based on a wetting approach. Chemical Engineering Science, Elsevier, 2014, 118, pp.245-256. ⟨10.1016/j.ces.2014.07.052⟩. ⟨hal-01274188⟩



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