h i g h l i g h t sMean bubble size, and size distribution in vertical gas-liquid Taylor vortex flow. Mass transfer coefficients for vertical gas-liquid Taylor vortex flow. Wall-driven shear produces prolate rather than oblate bubble shapes. Bubble size and spatial distribution explains low mass transfer coefficients. High wall area in annular geometry has significant impact on mass transfer. a b s t r a c tExperimental measurements of the volumetric liquid mass transfer and bubble size distribution in a vertically oriented semi-batch gas-liquid Taylor-Couette vortex reactor with radius ratio g = r i /r o = 0.75 and aspect ratio C = h/(r o À r i ) = 40 were performed, and the results are presented for axial and azimuthal Reynolds number ranges of Re a = 11.9-143 and Re H = 0-3.5 Â 10 4 , respectively. Based on these data, power-law correlations are presented for the dimensionless Sauter mean diameter, bubble size distribution, bubble ellipticity, and volumetric mass transfer coefficient in terms of relevant parameters including the axial and azimuthal Reynolds numbers. The interaction between wall-driven Taylor vortices and the axial passage of buoyancy-driven gas bubbles leads to significantly different dependencies of the mass transfer coefficient on important operating parameters such as inner cylinder angular velocity and axial superficial gas velocity than has been observed in horizontally oriented gas-liquid Taylor vortex reactors. In general, the volumetric mass transfer coefficients in vertical Taylor vortex reactors have a weaker dependence upon both the axial and azimuthal Reynolds numbers and are smaller in magnitude than those observed in horizontal Taylor vortex reactors or in stirred tank reactors. These findings can be explained by differences in the size and spatial distribution of gas bubbles in the vertically oriented reactor in comparison with the other systems.

Despite the groundbreaking advancements in the synthesis of inorganic lead halide perovskite (LHP) nanocrystals (NCs), stimulated from their intriguing size-, composition-, and morphology-dependent optical and optoelectronic properties, their formation mechanism through the hot-injection (HI) synthetic route is not well-understood. In this work, for the first time, in-flow HI synthesis of cesium lead iodide (CsPbI 3 ) NCs is introduced and a comprehensive understanding of the interdependent competing reaction parameters controlling the NC morphology (nanocube vs nanoplatelet) and properties is provided. Utilizing the developed flow synthesis strategy, a change in the CsPbI 3 NC formation mechanism at temperatures higher than 150 °C, resulting in different CsPbI 3 morphologies is revealed. Through comparison of the flow-versus flask-based synthesis, deficiencies of batch reactors in reproducible and scalable synthesis of CsPbI 3 NCs with fast formation kinetics are demonstrated. The developed modular flow chemistry route provides a new frontier for high-temperature studies of solution-processed LHP NCs and enables their consistent and reliable continuous nanomanufacturing for next-generation energy technologies.

The microscale multi-inlet vortex reactor (MIVR) has been developed for use in flash nanoprecipitation, a technique to generate functional nanoparticles. A scaled-up MIVR is motivated by the desire for a higher output of nanoparticles than the microscale reactor can provide. As the first step of this scaling process, the flow characteristics in a macro-scale MIVR have been investigated by stereoscopic particle image velocimetry. The studied Reynolds numbers based on the inlet geometry range from 3290 to 8225, resulting in a turbulent swirling flow within the reactor. The flow in the mixing chamber is found to be unstable with a wandering vortex center. The vortex wandering is constrained to a small area near the center of the reactor and has little effect on the mean velocity field. However, the measured turbulence kinetic energy and Reynolds stresses are found to be sensitive to the vortex wandering. The flow characteristics of the macro-scale MIVR are compared with the microscale MIVR in terms of swirl ratio and micromixing time. It is found that the swirl ratio and micromixing time of the flow increases as the MIVR is scaled up, indicating a flow with stronger swirl yet less mixing effectiveness in the scaled-up reactor. ■ INTRODUCTIONFunctional nanoparticles are of great scientific and industrial interest for their unique size-related properties and have a wide application in various areas, such as dyes, pesticides, and pharmaceuticals. 1 However, it is still challenging to produce functional nanoparticles in a relatively easy and inexpensive way. Flash nanoprecipitation (FNP) has been developed to produce functional nanoparticles with a narrow particle size distribution. 2 In the FNP technique, functional nanoparticles are formed by rapidly mixing a supersaturated organic active and a copolymer antisolvent, resulting in the organic active precipitation and particle growth where the growing particle size of the organic active is frozen by deposition of a block copolymer on its surface. 2 Mixing time in the FNP technique should be short enough to provide a uniform starting time for the precipitation. Two mixer geometries, the confined impinging jet reactor (CIJR) 3 and the multi-inlet vortex reactor (MIVR) 4 have been developed to meet the high demand of rapid mixing in FNP. While the CIJR is limited by the requirement of equal momenta of solvent and antisolvent streams, the MIVR is insensitive to the equality of the momentum from each stream, allowing the final fluid phase to be antisolvent dominant, which increases the stability of nanoparticles by depressing the rate of Ostwald Ripening. 4 Thus far, there have been many applications using the MIVR to produce functional nanoparticles. 5−9 To help understand the nanoprecipitation mechanism within the MIVR, mixing performance and flow characterization have been investigated in previous studies. Liu et al. 4 evaluated the mixing performance of a microscale MIVR by using a competitive reaction and computational fluid dynamics (CFD). Cheng et al. 10 measured fl...

Over the past decade, continuous flow reactors have emerged as a powerful tool for accelerated fundamental and applied studies of gas-liquid reactions, offering facile gas delivery and process intensification. In...

a b s t r a c tGas-liquid Taylor-Couette flow devices have attracted interest for use as chemical and biological reactors, and consequently the accurate prediction of interphase mass transfer coefficients is crucial for their design and optimization. However, gas-liquid mass transport in these systems depends on many factors such as the local velocity field, turbulent energy dissipation rate, and the spatial distribution and size of bubbles, which in turn have complicated dependencies on process, geometric, and hydrodynamic parameters. Here we overcome these problems by employing a recently developed and validated Eulerian two-phase CFD model to compute local values of the mass transfer coefficient based upon the Higbie theory. This approach requires good estimates for mass transfer exposure times, and these are obtained by using a novel approach that automatically selects the appropriate expression (either the penetration model or eddy cell model) based upon local flow conditions. By comparing the simulation predictions with data from corresponding oxygen mass transfer experiments, it is demonstrated that this adaptive mass transfer model provides an excellent description for both the local and global mass transfer of oxygen in a semibatch gas-liquid Taylor-Couette reactor for a wide range of azimuthal Reynolds numbers and axial gas flow rates.