Numerical and analytical models in electrohydrodynamics and microfluidics

在许多工业和研究过程中，电场和流体或气体的流动之间存在相互作用。除其他外，这种情况发生在所有涉及小颗粒的应用中，例如用于环境保护的静电除尘器。通常会产生一种称为电晕放电的现象来给粒子充电，这样就可以利用电动力来控制粒子的运动。电晕放电是一个复杂的物理过程，依赖于气体分子的雪崩电离，但它也会导致周围气体的运动，称为二次电流体流动，或离子风。这种流动有时是有益的，但通常是一种干扰设备预期功能的麻烦。在这两种情况下，数值模拟都有助于更好地了解这些复杂的现象，以及静电设备的设计和优化。此外，拟议的研究计划将首先处理一种新的数值算法和计算机程序的开发，该算法和计算机程序可用于模拟电晕放电。该算法将包括雪崩电离、附着和复合，以及纯气体和混合物中所有必要的离子反应和物种。建立一个高效、准确的电晕模型是进行气体流动分析的前提。流体-电场相互作用发挥重要作用的另一个领域是微流体。为了进行化学反应，需要处理少量的液体，无论是在微通道中连续流动的，还是以液滴的形式流动的。在所提出的研究方案中，将对数字微流体中的液滴变形和输运动力学进行数值模拟。微流体中流体的泵送可以通过许多不同的方式来实现，其中最有希望的是基于交流电渗透效应。目前文献中发表的关于这种效应的研究是基于一个极其简单化的模型。将开发一个新的更复杂的模型，其中将考虑到对这一过程的更完整的描述。然后将建立一个数值算法，并将研究流体泵的效率。

In many industrial and research processes there is an interaction between an electric field and flow of fluids or gases. Among others this happens in all applications involving small particles, for example in electrostatic precipitators used in environmental protection. A phenomenon called the electric corona discharge is typically generated to electrically charge the particles, so that electric forces can be used to control the particle's motion. The electric corona discharge is a complex physical process relying on avalanche ionization of the gas molecules, but it also results in motion of the ambient gas, called the secondary electrohydrodynamic flow, or ionic wind. This flow can be sometimes beneficial, but is often a nuisance disturbing the intended functioning of a device. In both cases numerical simulation can be helpful in garnering better understanding of these complex phenomena, and the design and optimization of electrostatic devices.   The proposed research program will first deal with the development of a new numerical algorithm and computer program, which can be used for simulation of the electric corona discharge. The algorithm will incorporate avalanche ionization, attachment and recombination, and all essential ionic reactions and species in pure gases and mixtures. An efficient and accurate corona model will be a prerequisite for the gas flow analysis. Another area where the fluid-electric field interaction plays an important role is microfluidics. Small amounts of fluid, either flowing continuously in a microchannel, or in the form of droplets, are handled in order to perform chemical microreactions. In the proposed research program, the dynamics of droplet deformation and transportation in digital microfluidics will be simulated numerically. Pumping of fluids in microfluidics can be achieved in many different ways and the most promising is based on the AC electroosmosis effect. Investigations of this effect published in the current literature are based on an extremely simplistic model. A new more complex model will be developed, which will take into account a more complete description of the process. Then a numerical algorithm will be created and the efficiency of fluid pumping will be investigated.