共查询到15条相似文献,搜索用时 46 毫秒
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研究了Y型微通道吸附型纳米颗粒稳定气泡的完全阻塞破裂的动力学,破裂过程可划分为挤压阶段和快速夹断阶段,两阶段内无量纲气泡最小颈部宽度与时间均呈幂率关系。气泡破裂过程的颈部动力学表明颗粒的存在并不影响两阶段转变的临界颈部宽度,但吸附在气泡表面的颗粒层会减弱挤压阶段中连续相对气泡颈部的挤压作用,以及快速夹断阶段角区中连续相液体回流对气泡的挤压作用,进而阻碍气泡颈部的形变,延长了气泡的破裂过程。纳米颗粒稳定的气泡的指前因子m及幂率指数α均小于常规气泡,但其差值随着毛细管数Ca和气泡长度l0的增大而减小,颗粒对气泡破裂过程的影响逐渐减弱。此外,纳米颗粒稳定的气泡的头部曲率略小于常规气泡,颗粒对完全阻塞破裂过程气泡头部动力学的影响可以忽略。 相似文献
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实验研究了T型微通道内浆料中气泡的生成过程和尺寸。聚丙乙烯微球浆料和N2分别为连续相和分散相。气泡的生成过程可分为三个阶段:膨胀阶段、挤压阶段和快速夹断阶段。随着浆料浓度的增大,膨胀阶段时长几乎没有变化,挤压阶段显著缩短,而快速夹断阶段略有缩短。在膨胀阶段和快速夹断阶段,气泡颈部宽度与无量纲剩余时间均呈幂率关系,而挤压阶段气泡颈部宽度与时间呈线性关系。考察了浆料浓度、气相和浆料流量对气泡生成尺寸的影响。结果表明气泡尺寸随气相流量的增大而增大,随液相流量和浆料浓度的增大而减小。 相似文献
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实验研究了T型微通道内浆料体系中弹状气泡的生成动力学,重点考察了颗粒粒径的影响。气泡的生成过程可划分为四个阶段:填充阶段、挤压阶段、过渡阶段和快速夹断阶段。在填充阶段、挤压阶段和快速夹断阶段,气泡最小颈部宽度与时间呈幂律关系。在过渡阶段,气泡最小颈部宽度与时间呈线性关系。浆料体系中气泡的挤压阶段和过渡阶段随颗粒粒径的减小而缩短。连续相流量及颗粒粒径对填充阶段幂律指数无显著影响;挤压阶段和快速夹断阶段的幂律指数以及过渡阶段的线性斜率均随颗粒粒径的增大而减小,随连续相流量的增大而增大。 相似文献
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利用高速摄像仪观察了聚焦十字型微通道内高黏度(630 mPa·s)的甘油-水溶液中氮气气泡的生成过程。研究了气泡生成过程以及气泡体积和最小颈部半径的变化规律。结果表明,高黏流体内气泡生成过程可分为回缩、膨胀、挤压和最终破裂4个阶段。气泡体积在膨胀和挤压阶段均随时间线性增长,但挤压阶段的斜率大于膨胀阶段的斜率。气泡最小颈部半径随时间变化分为两个不同的阶段:在挤压阶段,颈部半径随剩余时间呈幂率关系;而在最终破裂阶段,颈部半径随时间呈线性关系。 相似文献
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采用高速摄像仪对嵌入毛细管的阶梯式T型微通道内液滴和气泡的分散规律进行研究。考察了两相流量、黏度、表面活性剂浓度等因素对分散流型及分散尺寸的影响规律。结果表明,对于液滴分散过程,表面活性剂的浓度和连续相流量决定了分散流型,随二者增大,流型从dripping流向jetting流转变。对于气泡分散过程,实验范围内仅存在squeezing、dripping流型,表面活性剂的加入对气泡分散过程影响可忽略。嵌入毛细管的阶梯式T型微通道内获得的液滴、气泡直径小于微通道直径,根据实验结果基于两相流量和毛细管数分别建立了计算液滴、气泡分散尺寸的半经验模型,模型与实验结果符合良好。 相似文献
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采用高速摄像仪对聚焦十字型微装置内分散小气泡的生成进行了研究.方形截面微通道的尺寸分别为400pm×400μm和600μm×600μm.氮气为气相,加入表面活性剂十二烷基硫酸钠(soditm dodecyl sulfate,SDS)(0~0.5%(wt))的水-甘油(25%(wt),50%(wt),62%(wt))溶液... 相似文献
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微化学工程与技术是现代化学工程学科的前沿领域。微通道内液滴及气泡破裂动力学是决定多相过程并行微通道数目放大的基础与难点。破裂流型转换条件、界面动力学和尺寸调控等三方面是微通道内液滴与气泡破裂动力学的主要研究对象。讨论了对称微通道、非对称微通道、多级微通道、旁路微通道、含有障碍物的微通道内气泡和液滴破裂行为及影响因素,指出了目前微尺度下气泡与液滴破裂行为相关研究工作存在的不足,并对该领域未来的发展进行了展望。 相似文献
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利用高速摄像仪对T型微通道内浆料体系中的气泡生成频率和气泡尺寸进行了研究。以氮气作为分散相,含0.35%(质量分数)表面活性剂(SDS)不同浓度玻璃珠的甘油-水溶液为连续相。实验考察了弹状流下气液两相流量、颗粒浓度以及浆料表观黏度对气泡生成频率及气泡尺寸的影响。结果表明:在弹状流下,当分散相流量一定时,随着连续相流量的增大,气泡的生成频率增大而气泡尺寸减小。当连续相流量一定时,随着分散相流量的增大,气泡生成频率和气泡尺寸均增大。随着颗粒浓度的增大,浆料的表面张力减小,表观黏度增大,气泡生成频率增大而气泡尺寸减小。提出了T型微通道内浆料体系中生成气泡尺寸的预测模型,模型具有良好的预测精度。 相似文献
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Sheng Mi Shaokun Jiang Chunying Zhu Youguang Ma Taotao Fu 《American Institute of Chemical Engineers》2021,67(1):e17075
The step-emulsification devices with parallel microchannels are promising for the high-throughput formation of bubbles. However, the mechanism for bubble formation in such devices remains unclear. In present study, the mesoscale concept of compromise in a competition is used to reveal the mechanism. Nitrogen is used as the dispersed phase, and aqueous solutions with different viscosities are used as the continuous phase. The flow patterns and characteristic parameters for bubble formation are studied by using a high-speed camera. The characteristic parameters include the head distance of gas–liquid interface and the neck width, and the size and formation frequency of bubbles. Bubble formation is affected by the hydrodynamic feedback in the chamber and the interfacial evolution process, characterized by the relative magnitude of the evolution velocity for the head distance and the neck width of gaseous thread in both microchannels. It is found that the compromise effect is beneficial for the formation of bubbles with excellent monodispersity. 相似文献
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Sheng Mi Taotao Fu Chunying Zhu Shaokun Jiang Youguang Ma 《American Institute of Chemical Engineers》2020,66(1):e16777
Step-emulsification device is an emerging technology for bubble generation, which is convenient for numbering-up. However, the mechanism of bubble formation in such devices remains unclear. In this article, the mechanism of bubble formation in step-emulsification devices is investigated by using a high-speed camera. First, the evolution of gas–liquid interface with time during bubble formation is observed. Second, the variation of characteristic parameters of bubbles, such as bubble's volume VB and generation frequency f, with gas and liquid flow rates is described under various liquid viscosities and step widths. Meanwhile, the coupling law of interface evolution with characteristic parameters of bubbles is explored. Finally, the basic guideline for generation of monodispersed bubbles in step-emulsification is put forward: low liquid viscosity. Connecting the interface evolution with the characteristic parameters, predictive models for bubble's volume, and generation frequency in step-emulsification are proposed, respectively. 相似文献
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采用开源CFD软件OpenFOAM中的interFoam求解器对流动聚焦微通道内微液滴的形成过程进行了数值模拟。通过与文献中的实验数据进行对比,验证了VOF模型和幂律非牛顿流体模型的准确性。并以此为基础模拟了幂律剪切致稀流体中牛顿微液滴的形成过程,研究了幂律流体的幂律指数n和稠度系数K对微液滴生成的影响。研究表明,在滴状和挤压状流型中,离散线颈部宽度与周期内剩余时间呈幂律关系;离散线长度在坍塌阶段呈现线性缓慢增长,在夹断阶段呈现近似指数迅速增长的趋势。随着n和K的增大,液滴的尺寸逐渐减小,而生成频率则逐渐增大,且n的变化比K的变化对其产生的影响更明显。 相似文献
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The deformation of moving slug bubbles and its influence on the bubble breakup dynamics in microchannel were studied. Three bubble morphologies were found in the experiment: slug, dumbbell and grenade shapes. The viscosity effect of continuous phase aggravates the velocity difference between the fluid near the wall and the bubble, resulting in that the continuous phase near the bubble head flows towards and squeezes the bubble tail, which causes the deformation of bubbles. Moreover, the experimental results show that the deformation of bubbles could significantly prolong the bubble breakup period at the downstream Y-junction. There exists the critical capillary number CaCr for the asymmetric breakup of grenade bubbles, CaCr increases with the rise of flow rate and viscosity of the continuous phase. 相似文献