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        Chaotic behavior of in-line bubbles rising with coalescences in non-Newtonian fluids: A multiscale analysis

        Shaokun Jiang,Youguang Ma,Wenyuan Fan,Ke Yang,Huaizhi Li 한국화학공학회 2011 Korean Journal of Chemical Engineering Vol.28 No.1

        The nonlinear dynamics of in-line bubbles rising with coalescence in non-Newtonian Carboxymethylcellulose sodium (CMC) fluids was studied through the techniques such as the multiresolution signal decomposition and the chaotic time series analysis. The temporary signals of bubble passages collected by an optical sensing device at different heights were investigated by a 12-level wavelet decomposition and the scalewise characteristics of bubble motion were extracted and analyzed. The chaotic time series analysis distinguished the periodicity or the deterministic chaos of bubble motion successsfully. The calculation of Kolmogorov entropy proves that in the ranges of experimental heights and gas flowrates, the bubble rising dynamics becomes more chaotic with the increase of height, and reaches the maximum chaotic extent in a certain height, while with the further increase of height, the chaotic extent decreases slowly. With the increase of gas flowrate, at the lower height, the bubble rising dynamics changes from periodicity to deterministic chaos, and at the higher heights it reaches the maximum chaotic extent in a certain gas flowrate; however,for both cases, it has little change in the higher gas flowrates. Moreover, with the increase of CMC concentration, the bubble rising dynamics becomes less chaotic when the height is beyond a certain value.

      • KCI등재

        Comparison of formation of bubbles and droplets in step-emulsification microfluidic devices

        Wei Zhang,Ziwei Liu,Shaokun Jiang,Chunying Zhu,Youguang Ma,Taotao Fu 한국공업화학회 2022 Journal of Industrial and Engineering Chemistry Vol.106 No.-

        Monodispersed microbubbles and microdroplets are widely used as reaction carriers in microfluidics. Inthis study, the generation processes of bubbles and droplets in a step-emulsification microfluidic deviceare compared to show the similarities and differences in the emulsification process. By changing theplacement of the microdevice, the effects of buoyancy and gravity on the generation of bubbles and dropletsare introduced, and the feedback mechanism of the bubble layer and the effect of droplet accumulationon the emulsification process are clarified. Finally, based on the analysis of the difference of thepinch-off of the dispersed phase between the bubble and the droplet in this configuration, the Plateau-Rayleigh instability processes for the formation of bubble and droplet are revealed by using a highspeedcamera system, and the reasons for the difference of the operating ranges of the gas flow rateand liquid flow rate in the dripping flow regime are explained.

      • KCI등재

        Microfluidic step emulsification techniques based on spontaneous transformation mechanism: A review

        Ziwei Liu,Cong Duan,Shaokun Jiang,Chunying Zhu,Youguang Ma,Taotao Fu 한국공업화학회 2020 Journal of Industrial and Engineering Chemistry Vol.92 No.-

        Rapid and robust generation of uniformly sized droplets is a research hotspot for emulsificationtechnology. Compared with conventional microfluidic devices such as cross-junction andflow-focusing,the size of the droplets generated in the step emulsifiers based on the spontaneous transformationmechanism is independent of theflowfluctuation, making this type of devices have many advantagesand important application value. To introduce the research progress of step emulsification technology inrecent years, this review discusses the device configurations, interfacial evolution for droplet formationmechanism,flow pattern classification, the influence of control variables on the emulsification processand the application advantages of such devices, and illustrates the design and selection principles of suchdevices, the control laws of manipulation variables, and the future applicationfields and directions.

      • KCI등재

        Bubble formation in a step-emulsification microdevice: hydrodynamic effects in the cavity

        Zhiwei Zhang,Zhongdong Wang,Fengrui Bao,Mengyu Fan,Shaokun Jiang,Chunying Zhu,Youguang Ma,Taotao Fu 한국공업화학회 2021 Journal of Industrial and Engineering Chemistry Vol.94 No.-

        This study focuses on the generation of bubbles in a step-emulsification microdevice via a two-anglephotography method. It's found that the bubble generation mechanism is controlled by the interfacialtension, below a critical capillary number; while controlled by viscous force, inertial force and thedisturbance induced by the bubble swarm, above the critical capillary number. From the two-anglephotography method, a model is established for predicting the bubble size, by taking into account of thedynamic contact angle between gas-liquid interface and wall, and the hydrodynamic feedback of thecavity on bubble formation via the quantification of resistance by the volume fraction of gas in the cavity.

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