Abstract: In this study, droplet characteristics including droplet length and formation time, and mixing efficiency in droplets were investigated via the volume of fluid (VOF) method coupled with a user defined scalar (UDS) model. A cross-shaped junction with a square cross-section was designed and used for droplet formation. An initial arrangement which differed from that of a conventional operation was adopted. Results show that when the droplet superficial velocity is constant, the exchange between the dispersed phase velocity and the continuous phase velocity has a marginal effect on the droplet formation time. However, the exchange has a great effect on droplet length. These findings provide a valuable guide for future operation of droplet formation. In addition, the results show that the mixing efficiency in the droplet forming stage can be classified into time-dominated and length-dominated regimes according to the droplet superficial velocity. When a droplet flows in a microchannel, a higher droplet superficial velocity increases mixing efficiency due to the faster inner circulation and shorter droplet length.

微通道内液滴表面流速对混合效率的影响分析

[1]ArjunA, AjithRR, RanjithSK, 2020. Mixing characterization of binary-coalesced droplets in microchannels using deep neural network. Biomicrofluidics, 14(3):034111.

[2]BaiL, ZhaoSF, FuYH, et al., 2016. Experimental study of mass transfer in water/ionic liquid microdroplet systems using micro-LIF technique. Chemical Engineering Journal, 298:281-290.

[3]BaiL, FuYH, YaoM, et al., 2018. Enhancement of mixing inside ionic liquid droplets through various micro-channels design. Chemical Engineering Journal, 332:537-547.

[4]BorgohainP, ChoudharyD, DalalA, et al., 2018. Numerical investigation of mixing enhancement for multi-species flows in wavy channels. Chemical Engineering and Processing-Process Intensification, 127:191-205.

[5]CaoYR, AdriaenssensB, deA. Bartolomeu A, et al., 2020. Accelerating sulfonyl fluoride synthesis through electrochemical oxidative coupling of thiols and potassium fluoride in flow. Journal of Flow Chemistry, 10(1):191-197.

[6]CaoZ, WuZ, SundénB, 2018. Dimensionless analysis on liquid-liquid flow patterns and scaling law on slug hydrodynamics in cross-junction microchannels. Chemical Engineering Journal, 344:604-615.

[7]ChristopherGF, NoharuddinNN, TaylorJA, et al., 2008. Experimental observations of the squeezing-to-dripping transition in T-shaped microfluidic junctions. Physical Review E, 78(3):036317.

[8]DaiS, LuoJH, LiJ, et al., 2017. Liquid–liquid microextraction of Cu²⁺ from water using a new circle microchannel device. Industrial & Engineering Chemistry Research, 56(44):12717-12725.

[9]DengNN, SunSX, WangW, et al., 2013. A novel surgery-like strategy for droplet coalescence in microchannels. Lab on a Chip, 13(18):3653-3657.

[10]FuYH, WangH, ZhangX, et al., 2019. Numerical simulation of liquid mixing inside soft droplets with periodic deformation by a lattice Boltzmann method. Journal of the Taiwan Institute of Chemical Engineers, 98:37-44.

[11]Hosseini KakavandiF, RahimiM, JafariO, et al., 2016. Liquid–liquid two-phase mass transfer in T-type micromixers with different junctions and cylindrical pits. Chemical Engineering and Processing-Process Intensification, 107:58-67.

[12]JinZJ, QiuC, JiangCH, et al., 2020. Effect of valve core shapes on cavitation flow through a sleeve regulating valve. Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 21(1):1-14. http://doi.org/10.1631/jzus.A1900528

[13]KorczykPM, van SteijnV, BlonskiS, et al., 2019. Accounting for corner flow unifies the understanding of droplet formation in microfluidic channels. Nature Communications, 10(1):2528.

[14]LiuYY, ZhaoQK, YueJ, et al., 2021. Effect of mixing on mass transfer characterization in continuous slugs and dispersed droplets in biphasic slug flow microreactors. Chemical Engineering Journal, 406:126885.

[15]LuoXM, YinHR, RenJ, et al., 2019. Enhanced mixing of binary droplets induced by capillary pressure. Journal of Colloid and Interface Science, 545:35-42.

[16]MadadelahiM, ShamlooA, 2017. Droplet-based flows in serpentine microchannels: chemical reactions and secondary flows. International Journal of Multiphase Flow, 97:186-196.

[17]MehtaV, RathSN, 2021. 3D printed microfluidic devices: a review focused on four fundamental manufacturing approaches and implications on the field of healthcare. Bio-Design and Manufacturing, 4(2):311-343.

[18]MuXT, JuXJ, ZhangL, et al., 2019. Chitosan microcapsule membranes with nanoscale thickness for controlled release of drugs. Journal of Membrane Science, 590:117275.

[19]NiculescuAG, ChircovC, BircaAC, et al., 2021. Fabrication and applications of microfluidic devices: a review. International Journal of Molecular Sciences, 22(4):2011.

[20]NisisakoT, ToriiT, HiguchiT, 2004. Novel microreactors for functional polymer beads. Chemical Engineering Journal, 101(1-3):23-29.

[21]OishiM, KinoshitaH, FujiiT, et al., 2009. Confocal micro-PIV measurement of droplet formation in a T-shaped micro-junction. Journal of Physics: Conference Series, 147:012061.

[22]ÖzkanA, ErdemEY, 2015. Numerical analysis of mixing performance in sinusoidal microchannels based on particle motion in droplets. Microfluidics and Nanofluidics, 19(5):1101-1108.

[23]QianJY, LiXJ, GaoZX, et al., 2019a. Mixing efficiency analysis on droplet formation process in microchannels by numerical methods. Processes, 7(1):33.

[24]QianJY, LiXJ, GaoZX, et al., 2019b. Mixing efficiency and pressure drop analysis of liquid-liquid two phases flow in serpentine microchannels. Journal of Flow Chemistry, 9(3):187-197.

[25]QianJY, ChenMR, LiuXL, et al., 2019c. A numerical investigation of the flow of nanofluids through a micro Tesla valve. Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 20(1):50-60. http://doi.org/10.1631/jzus.A1800431

[26]QianJY, MuJ, HouCW, et al., 2021. A parametric study on unbalanced moment of piston type valve core. Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 22(4):265-276. http://doi.org/10.1631/jzus.A2000582

[27]Sattari-NajafabadiM, Nasr EsfahanyM, WuZ, et al., 2017. Hydrodynamics and mass transfer in liquid-liquid non-circular microchannels: comparison of two aspect ratios and three junction structures. Chemical Engineering Journal, 322:328-338.

[28]SuYH, ZhaoYC, ChenGW, et al., 2010. Liquid-liquid two-phase flow and mass transfer characteristics in packed microchannels. Chemical Engineering Science, 65(13):3947-3956.

[29]TanthapanichakoonW, AokiN, MatsuyamaK, et al., 2006. Design of mixing in microfluidic liquid slugs based on a new dimensionless number for precise reaction and mixing operations. Chemical Engineering Science, 61(13):4220-4232.

[30]TiceJD, SongHL, LyonAD, et al., 2003. Formation of droplets and mixing in multiphase microfluidics at low values of the Reynolds and the capillary numbers. Langmuir, 19(22):9127-9133.

[31]TsaoulidisD, AngeliP, 2015. Effect of channel size on mass transfer during liquid-liquid plug flow in small scale extractors. Chemical Engineering Journal, 262:785-793.

[32]WangJJ, WangJN, FengLF, et al., 2015. Fluid mixing in droplet-based microfluidics with a serpentine microchannel. RSC Advances, 5(126):104138-104144.

[33]WuJY, YueY, LiJY, et al., 2022. Circumferential design of throttling window of main feed water regulating valve and its influence on flow characteristics. Chinese Journal of Engineering Design, 29(1):74-81 (in Chinese).

[34]YehSI, SheenHJ, YangJT, 2015. Chemical reaction and mixing inside a coalesced droplet after a head-on collision. Microfluidics and Nanofluidics, 18(5-6):1355-1363.

[35]ZhangJ, XuWH, XuFY, et al., 2021. Microfluidic droplet formation in co-flow devices fabricated by micro 3D printing. Journal of Food Engineering, 290:110212.

[36]ZhangPF, XuXG, HuaYJ, et al., 2022. Effects of the outlet pressure on two-phase slug flow distribution uniformity in a multi-branch microchannel. Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 23(1):68-82.

[37]ZhangQ, LiuHC, ZhaoSN, et al., 2019. Hydrodynamics and mass transfer characteristics of liquid–liquid slug flow in microchannels: the effects of temperature, fluid properties and channel size. Chemical Engineering Journal, 358:794-805.

[38]ZhangY, ZhangXB, XuBJ, et al., 2015. CFD simulation of mass transfer intensified by chemical reactions in slug flow microchannels. The Canadian Journal of Chemical Engineering, 93(12):2307-2314.