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Bubble formation in high-viscosity liquids in step-emulsification microdevices
Sheng Mi,Chunying Zhu,Abdelkarim Chaouiki,Taotao Fu 한국공업화학회 2022 Journal of Industrial and Engineering Chemistry Vol.114 No.-
Bubble formation in high-viscosity liquids in step-emulsification microdevices is presented. Nitrogen isused as the dispersed phase. Glycerol aqueous solutions with concentration more than 60% (w/w) areused as the continuous phase to show the effect of high viscosity liquid. It was found that the transitionof flow patterns of gas–liquid two-phase flow can be divided into two categories: bubbly flow and parallelflow. Compared with the cases in low viscosity liquid, the wettability with wall was deteriorated andthe resistance in chamber were enhanced, greatly. All of these effects cause different performance ofinterface evolution during bubble formation and the volume and formation frequency after pinchingoff. Therefore, the relative magnitude of pressure variation between chamber and gas inlet was changedto affect the flow pattern and monodispersity when the operation conditions were changed.
Rongwei Guo,Chunying Zhu,Yaran Yin,Taotao Fu,Youguang Ma 한국공업화학회 2019 Journal of Industrial and Engineering Chemistry Vol.75 No.-
The gas–liquid two-phaseflow and mass transfer performance of CO2 absorption into 2-amino-2-methyl-1-propanol (AMP) with ethylene glycol (EG) non-aqueous solution in a microchannel wereinvestigated under different gas–liquid two-phaseflow rates and AMP concentrations. A new correlationwas proposed for accurately predicting the liquid side volumetric mass transfer coefficient by consideringthe enhancement factor. It was verified that the volumetric mass transfer coefficient of CO2 absorption inthe microchannel is obviously higher than that in the traditional macroscopic column. Therefore, withthe usage of microchannel for AMP-EG non-aqueous solution, both low energy consumption and highefficient absorption could be reached.
Asymmetrical breakup and size distribution of droplets in a branching microfluidic T-junction
Pengcheng Ma,Taotao Fu,Chunying Zhu,Youguang Ma 한국화학공학회 2019 Korean Journal of Chemical Engineering Vol.36 No.1
The breakup and distribution of droplets at a branching T-junction were investigated experimentally by a high-speed camera. The effects of two-phase flow rates, two-phase Reynolds number and capillary number of the dispersed phase on droplet volume distribution were studied. The results indicated that the volume distribution ratio decreases first and then increases with the increase of two-phase flow ratio Qd/Qc. Similarly, as the Reynolds number Rec of the continuous phase increases, the volume distribution ratio also decreases at first and then increases. The increase of Reynolds number Red of the dispersed phase would lead to a reduction in the volume distribution ratio . Moreover, the increase of the capillary number Cad of dispersed phase could result in an increase in the volume distribution ratio . Correlations for predicting the volume distribution ratio were proposed, and the calculated results show good agreement with experimental data.
Alterations of oral microbiota in Chinese children with viral encephalitis and/or viral meningitis
Li Yijie,Liu Jing,Zhu Yimin,Peng Chunying,Dong Yao,Liu Lili,He Yining,Lu Guoping,Zheng Yingjie 한국미생물학회 2022 The journal of microbiology Vol.60 No.4
The role of oral microbiota in viral encephalitis and/or viral meningitis (VEVM) remains unclear. In this hospital-based, frequency-matched study, children with clinically diagnosed VEVM (n = 68) and those with other diseases (controls, n = 68) were recruited. Their oral swab samples were collected and the oral microbiota was profiled using 16S rRNA gene sequencing. The oral microbiota of children with VEVM exhibited different beta diversity metrics (unweighted UniFrac distance: P < 0.001, R2 = 0.025, Bray-curtis dissimilarity: P = 0.045, R2 = 0.011, and Jaccard dissimilarity: P < 0.001, R2 = 0.017) and higher relative abundances of taxa identified by Linear discriminant analysis (LDA) with effect size (Enterococcus, Pedobacter, Massilia, Prevotella_9, Psychrobacter, Butyricimonas, Bradyrhizobium, etc., LDA scores > 2.0) when compared with the control group. The higher pathway abundance of steroid hormone biosynthesis predicted by oral microbiota was suggested to be linked to VEVM (q = 0.020). Further, a model based on oral microbial traits showed good predictive performance for VEVM with an area under the receiver operating characteristic curve of 0.920 (95% confidence interval: 0.834–1.000). Similar results were also obtained between children with etiologically diagnosed VEVM (n = 43) and controls (n = 68). Our preliminary study identified VEVM-specific oral microbial traits among children, which can be effective in the diagnosis of VEVM.
Manipulation of microdroplets at a T-junction: Coalescence and scaling law
Rui Ma,Qindan Zhang,Taotao Fu,Chunying Zhu,Kai Wang,Youguang Ma,Guangsheng Luo 한국공업화학회 2018 Journal of Industrial and Engineering Chemistry Vol.65 No.-
The manipulation of a droplet at a microfluidic T-junction is achieved via adding reagents into the droplet with the same solution. Three types for droplet coalescence at the T-junction were observed: tail coalescence, slipping coalescence and unsteady coalescence behaviors with a new droplet formation. The final droplet size decreased (increased) with increasing the capillary number when the flow rate of the dispersed (continuous) phase was fixed. The final droplet size increased with increasing the capillary number of the added phase. The correlations for predicting the coalesced droplet size for tail and slipping coalescence were proposed.
Breakup dynamics of ferrofluid droplet in a microfluidic T-junction
Rui Ma,Taotao Fu,Qindan Zhang,Chunying Zhu,Youguang Ma,Huai Z. Li 한국공업화학회 2017 Journal of Industrial and Engineering Chemistry Vol.54 No.-
This paper investigated the breakup dynamics of ferrofluid droplet in a microfluidic T-junction with the magnetic field. Droplet breakup types with permanent obstruction, part obstruction and without obstruction were observed. The droplet breakup processes with permanent and part obstruction could be divided into squeezing, transition and pinch-off stages. The minimum width of droplet neck could be scaled as power-law relationships with time for squeezing stage and with remaining time for the last two stages. The droplet breakup process without obstruction has only last two stages. The results show that the magnetic field could affect the dynamics of droplet breakup.
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.
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.
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.