【Frontiers in HaiChuan Chemical Technology】New advances have been made in the regulation of flow and mass transfer of highly viscous non-Newtonian polymer fluids in microchannels at Xi’an Jiaotong University

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New progress has been made in the regulation of flow and mass transfer of high-viscosity non-Newtonian polymer fluids in microchannels at Xi’an Jiaotong University. The droplet/bubble formation and interfacial mass transfer processes of high-viscosity non-Newtonian polymer fluids in microchannels are key scientific issues in the enhancement of microreactors and the controlled preparation of functional materials. To address challenges such as fracture instability caused by complex rheological properties and unclear mass transfer mechanisms, a team led by Researcher Yuan Wenjun and Professor Chen Fei from the School of Chemical Engineering at Xi’an Jiaotong University conducted experimental and numerical simulation studies on the control of polymer droplet formation and the enhancement of gas-liquid mass transfer. Regarding droplet formation, a vibration-assisted active control strategy was proposed, which revealed that vibrations induce local vortices in the necking region, enhance shear forces and reduce the apparent viscosity, thereby facilitating the stable fragmentation and uniform droplet formation of highly viscous shear-thinning polymer fluids. The optimal vibration frequency matches the maximum growth rate of interface instability, resulting in a reduction of the size coefficient of variation of the prepared microspheres by up to 7.8 times. In terms of gas-liquid mass transfer, the coupled effects of zero-shear viscosity and time constant on bubble dynamics and mass transfer efficiency were elucidated; the volume mass transfer coefficient kLa varied by up to a factor of 3, and a corresponding prediction model was established. Relevant studies provide theoretical and practical support for the regulation of flow and mass transfer in microchemical processes involving complex polymer fluids. Relevant results were published in AIChE J and CES journals: Regulation of droplet formation in vibration-assisted shear-thinning polymer fluids was achieved using a coaxial co-flow microfluidic device, with the shear-thinning polymer solution as the dispersed phase and the PVA aqueous solution as the continuous phase, and mechanical vibrations were employed to regulate disturbances at the inlet of the continuous phase ； By combining experiments, theoretical analysis, and 3D numerical simulations, the droplet breakage process is analyzed using the VOF method and adaptive mesh refinement, while a power-law model is employed to describe the rheological properties of polymer fluids. The main conclusions are as follows: Mechanical vibration can effectively regulate droplet formation in shear-thinning polymer fluids within microchannels. Vibration induces local vortices in the necking zone, enhancing local shear and reducing the apparent viscosity, thereby accelerating droplet breakup ； The optimal vibration frequency matches the maximum growth rate of Rayleigh-Plateau instability. A unified flow pattern criterion and droplet size scaling relationship were established. The boundary between the uniform droplet region and the random droplet region can be quantitatively predicted based on the composite dimensionless group We_d (η_d/η_c )^0.09 and Ca_c^0.2 Re_o^0.8 ； The relative deviation of the established droplet size prediction model is kept within ±10%. The vibration-assisted strategy significantly improved the monodispersity of droplets and microspheres of highly viscous polymer fluids. For the three molecular weight systems, the coefficient of variation in microsphere size decreased from 10.95% to 1.40%, from 14.51% to 4.29%, and from 21.46% to 2.78%, providing a reliable method for the preparation of highly homogeneous polymer microparticles. Read this chapter in the novel reader – go and read it; immerse yourself in reading within the novel reader