Nowadays, multiphase flows occur in many different applications in everyday life or industrial context. Consequently, the understanding of transport phenomenolgy between the participating phases is a crucial task of recent and prospective research. When it comes to the optimization of absorption and chemical reaction tasks in process industry, in‐depth knowledge concerning mass transfer is required. The laser‐induced fluorescence (LIF) imaging is therefore a promising optical measurement technique to characterize concentration fields with high spatial and temporal resolution. This review gives an overview of the different fields of research within which LIF measurements are carried out, with focus on gas‐liquid systems. Chances and obstacles of recently publicated results as well as experiences of LIF methods regarding multiphase flows are presented and discussed.
In most chemical reactors the homogeneous distribution of reactants is a desired prerequisite for guaranteed product quality and purity. However, oftentimes, especially in new reactor concepts this condition may not be met due to evolving or existing structures in the transport patterns. In this article the usage of Lagrangian analysis techniques in order to analyze chemical and biochemical reactors regarding the behavior of Lagrangian tracers is explored. A Lagrangian analysis on two different datasets is performed trying to show the large versatility of the concepts. The Lagrangian analysis techniques allow new insights into the reactor dynamics and could be a valuable tool to identify and characterize areas of different mixing performance.
Precisely designed structures inserted in hybrid reactors can be used to control multiphase hydrodynamics and to act as a catalyst carrier simultaneously. While numerical simulations with computational fluid dynamics have limitations regarding the complex interactions in multiphase flows, performing experiments using rapid prototyping (RP) offers the possibility of a fast fabrication and verification of tailor-made structures for specific flow characteristics, efficient mass transport, and high conversion rates. In the presented work, the development of a countercurrently operated additively manufactured reactor for the decarboxylation of ferulic acid to 2-methoxy-4-vinylphenol (MVP) along in situ extraction with n-heptane is shown. Here, the use and optimization of periodic open-cell structures (POCSs) as a carrier for the enzyme phenolic acid decarboxylase and a distributor for the extraction phase are targeted. By RP of transparent structures and their examination concerning the induced flow characteristics of colored heptane, a structure could be optimized for the specific reaction system. The additive manufacturing of POCSs and their application in a hybrid countercurrently operated reactor enabled the conversion of FA and a low concentration of the competitively inhibiting product MVP in the reaction phase via efficient in situ extraction via the dispersed heptane phase.
In chemical process engineering, fast gas‐liquid reactions often suffer from an inefficient distribution of gas and therefore mixing and mass transfer performance. This study deals with the possibility of influencing the local gas holdup and bubble size distribution in a gas‐liquid process using additively manufactured lattice structures (AMLS). The used measuring technique to study bubble size, velocity, and the local gas holdup is a photo‐optical needle probe. By using AMLS, a significant radial homogenization of the local gas holdup and the mean bubble size is achieved. Furthermore, it can be demonstrated that the bubble size can be tailored by the geometry of the inserted structure. It is illustrated that the mean bubble velocities are lowered within the lattice resulting in a higher residence time of the dispersed phase with an impact on the mass transfer performance within the AMLS.
Smart materials possess a high potential for application in process engineering. Among these smart materials, stimuli-responsive hydrogels exhibit the chemically inherent characteristic to significantly change their macroscopic properties through shifts in environmental conditions. This enables response-triggered actuation caused by a reaction or process deviation. Thereby, smart process concepts are facilitated, which are capable of self-contained process control without external input. Through additive manufacturing of responsive hydrogels, intricate geometries can be generated, with which the response-triggered actuation can perform sophisticated control tasks. Periodic open-cell structures are such geometries, which improve the mass transport in multiphase flows through the distribution of the disperse phase. Responsive hydrogels fabricated as periodic open-cell structures enable the actuation of multiphase flows through an environmental switch allowing for adjustment of flow conditions. Herein, we demonstrate the application of switchable smart structures that facilitate the adaptation of fluid-dynamic properties and mass transfer in cocurrent gas–liquid flows depending on environmental conditions. Smart structures, which are additively manufactured from acrylate photoresist formulations, are applied for in situ and in operandi adjustment of phase distribution through expansion and collapse of these structures in flow channels. Further, diverse photoresist formulations with different associated response triggers are shown, which demonstrate the versatility for application as an in situ and in operandi switch for mass transfer in process units operating with multiphase flows.
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