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101.
在T形微通道中,以错流剪切的分散方式实现了微米级分散气泡的制备,并以NaOH水溶液吸收CO2为对象,考察了气.液微分散体系的分散规律和传质性能.通过考察两相流速对气泡分散尺寸的影响,建立了预测气泡形成尺寸的数学模型.根据气泡的初始分散尺寸、流动阶段的体积变化以及传质完成后的尺寸,首次测定和区分了气泡形成阶段和运动阶段的传质量,建立了原位测定气泡分散流传质系数札的方法,并考察了两相流量对札的影响.结果表明,由于微通道中气泡的形成时间很短,形成阶段的传质量在总传质量中所占的比例很低.气泡分散流的传质系数主要受液相流量的影响,气相流量的影响基本可以忽略.基于实验结果,建立了计算传质系数鼠的无因次准数关联,计算结果与实验结果符合良好. 相似文献
102.
运用改进的耗散粒子动力学方法模拟了液滴在由凹槽所构成的粗糙表面微通道内的运动行为.改进的耗散粒子动力学方法采用新近提出的一种短程排斥、长程吸引相互作用势能函数,从而可以模拟带有自由面的流体,如液滴等.模拟了新势能函数下液滴与固体壁面的静态接触角,并用2次多项式拟合了"接触角-awf/af"变化曲线.研究了液滴在带凹槽的微通道中运动时,微通道壁面浸润性、外场力、液滴温度对液滴流动特性的影响.研究表明壁面浸润性和外场力对液滴流动特性的影响较大,液滴温度对液滴流动特性的影响较小.研究结果对运用耗散粒子动力学方法模拟并分析微流体在复杂微通道的流动有一定的参考价值. 相似文献
103.
IEF is a high-resolution separation method taking place in a medium with continuous pH gradients, which can be set up by applying electrical field to the liquid in a diverging microchannel. The axial variation of the channel cross-sectional area will induce nonuniform Joule heating and set up temperature gradient, which will generate pH gradient when proper medium is used. In order to operationally control the thermally generated pH gradients, fundamental understanding of heat transfer phenomena in microfluidic chips with diverging microchannels must be improved. In this paper, two 3-D numerical models are presented to study heat transfer in diverging microchannels, with static and moving liquid, respectively. Through simulation, the temperature distribution for the entire chip has been revealed, including both liquid and solid regions. The model for the static liquid scenario has been compared with published results for validation. Parametric studies have showed that the channel geometry has significant effects on the peak temperature location, and the electrical conductivity of the medium and the wall boundary convection have effects on the generated temperature gradients and thus the generated pH gradients. The solution to the continuous flow model, where the medium convection is considered, shows that liquid convection has significant effects on temperature distribution and the peak temperature location. 相似文献
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降低微通道板噪声和增加其电子增益是改善微光像增强器信噪比、视场清晰度和亮度增益最好的技术途经之一。采用具有高而且稳定的二次电子发射系数的皮料玻璃和与皮料玻璃的热物理性能相匹配且化学腐蚀速率比皮料大4个数量级的芯料玻璃以及与两者在一切工艺过程相匹配的实体边玻璃,通过优化实体边实芯工艺制作出的高性能微通道板,其暗电流密度小于5×10-13A/cm2,固定图案噪声和闪烁噪声明显降低;在真空系统中,经40μAh电子清刷后,电子增益(800V)大于500。制管实验表明:这种微通道板达到了预期效果。 相似文献
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109.
The slipflow model is usually used to study microflows when the Knudsen number lies between 0.01 and 0.1. The instability
due to microscale effect seems to have never been studied before. In this paper we present preliminary results for the instability
(not physical instability) of this model when applied to microchannel flow with a vanishing Reynolds number. The present paper
is restricted to symmetrical mode. Both first-order and second-order slip boundary conditions will be considered.
The project supported by the National Natural Science Foundation of China (10025210) and Tsinghua Project for Basic Research
(2002) 相似文献
110.
We report a contraction-expansion array (CEA) microchannel that allows inertial size separation by a force balance between inertial lift and Dean drag forces in fluid regimes in which inertial fluid effects become significant. An abrupt change of the cross-sectional area of the channel curves fluid streams and produces a similar effect compared to Dean flows in a curved microchannel of constant cross-section, thereby inducing Dean drag forces acting on particles. In addition, the particles are influenced by inertial lift forces throughout the contraction regions. These two forces act in opposite directions each other throughout the CEA microchannel, and their force balancing determines whether the particles cross the channel, following Dean flows. Here we describe the physics and design of the CEA microfluidic device, and demonstrate complete separation of microparticles (polystyrene beads of 4 and 10 μm in diameter) and efficient exchange of the carrier medium while retaining 10 μm beads. 相似文献