Design, fabrication and experimental research for an electrohydrodynamic micropump

Abstract

This paper presented a novel electrohydrodynamic (EHD) micropump based on MEMS technology. The working mechanisms and classification of EHD micropump were introduced. The fabrication process of EHD micropump was presented with the material selection, optimal design of microelectrode and assembly process. Static pressure experiments and flow experiments were carried out using different fluid and the channel depth. The results indicated that the micropump could achieve a maximum static pressure head of 268 Pa at an applied voltage of 90 V. The maximum flow rate of the micropump-driven fluid could reach 106 μL/min. This paper analyzed the future of combining micropump with heat pipe to deal with heat dissipation of high power electronic chips. The maximum heat dissipation capacity of 87 W/cm 2 can be realized by vaporizing the micropump-driven liquid on vaporizing section of the heat pipe. electrohydrodynamic (EHD), MEMS, micropump, electronic coolingCitation:

A systematic overview of electrode configuration in electric‐driven micropumps

“…Consequently the fluid loses local electroneutrality, after that, EHD flow is generated. He et al [87] proposed a new micropump configuration to investigate various characteristics such as electrode geometry (sawtooth-shaped), electrode materials, working fluid (i.e., HFE7100 and ethyl alcohol), and depth of microchannel (from 50 to 200 µm) (Figure 14). In their electrode fabrication, two various fabrication workflows were employed: the kit-off and the electroplating process.…”

Overview of electrohydrodynamic conduction pumping

“…Yazdani 和 Seyed-Yagoobi [28,[135][136][137][138][139] 利用传导机制，产 生高速射流冷却加热表面、进行球型储液器的热均匀 化处理以及增强流速通道来流的强迫对流，提高系 统的散热能力。 Nourdanesh 与 Esmaeilzadeh [140] 采用平 嵌电极泵送煤油，进行传导强化对流散热与自然对 流散热对比实验研究。Nourdanesh 等 [141] 在文献 [140] [142,143] 构建了一种新型的 EHD 传导强化双管换热器， 在冷却管中布置平嵌电极，增强液体对流换热。 图 25 嵌入纺织手套中，用于调节体温的可伸缩泵 [33] Fig 25 Stretchable pump embedded in a textile glove for on-body thermal regulation [33] Cacucciolo 等 [33] 将柔性泵嵌入在纺织手套内，进 行体温热调节，如图 腾时，性能几乎不受重力的影响 [146] 。实验结果有力 地证实了电导泵长期应用于航空散热系统的应用前 景。传导机制还可应用于提高池沸腾临界热流密度、 强化沸腾传热 [147][148][149][150] 。Pearson 和 Seyed-Yagoobi [151] 创 新设计了同心环形的结合电极布置，使容器周围液 体从不同方向流向中心加热蒸发区。在给定热通量的 条件下，传导机制产生可观的循环速度湿润中心液 体沸腾区与液膜几乎停滞无传导机制的状态相比， 蒸发器表面液体过热温度显著降低。 图 26 液体薄膜沸腾实验系统 [152] Fig 26 Experimental system of liquid film boiling [152] 为 [21,[153][154][155] 基于 MEMS 加工技术制作的微注入泵、华南理工 大学万珍平等 [58] 基于微加工制作的一种微电导泵。山 东大学李斯盟等 [156]…”

“…产生连续流动的特性，实现电能和流体动能的直接 相互转换 [6,7] 。这类泵的优点包括:(1)可通过改变电 场实现快速、 智能主动控制(2)无机械运动部件、 设 计简单、重量轻(3)适用于低重力空间等特殊环境 (4)适用于单相和多相流(5)流体电流小，能耗 低(6)无振动、低噪音等 [8,9] [10,11] ( injection/ion-drag pump)、 感应泵 [12,13] (induction pump)和传导泵 [14,15] (conduction pump)。电渗泵(electroosmotic pump) 也是一种库仑力驱动泵 [16,17] 。与电流体泵中库仑力作 用于液体内部的离子不同，电渗泵中库仑力作用于 固-液界面双电层内的离子。通常电渗泵的特征尺寸 小，泵送的液体电导率高，电场方向一般沿着管道 边界。另外，还存在其它类型的电流体泵，如第二类 电渗泵 [18] 、由离子浓度差驱动的泵 [19] 、由昂萨格-维恩 (Onsager-Wien)效应驱动的泵 [20] 孔-圆环电极 [23] , (b)和(d)尺寸不同的平嵌电极 [24] Fig 1 Schematic and physical diagrams of two typical asymmetric electrode arrangement, (a) and (c)perforated disk electrodes [23] , (b) and (d) flushed electrodes [24] 电流体注入泵中，电极-液体界面的电化学反应 形成同号电荷层(homocharge layer)，自由电荷在 电场作用下进入液体内部并沿电场线迁移，拖曳周 围的流体产生流动。此种泵研究的最早、最充分，但 电荷注入可能会改变流体工质的化学组成和电极表 面性质，从而影响泵性能的稳定性和寿命。例如，于 翮等人 [21] 研制的微型注入泵运行了 20 分钟后即发生 性能衰减并失效。感应泵中，自由电荷来源于电导率 空间不均匀性，行波交流电场对电荷的吸引和排斥 作用引起流体流动。感应泵的工质一般为非等温流体 (电导率随温度变化)或气-液两相流(电导率在相 分界处有阶跃)，不适用于单相等温液体 [6] 。 电导泵中的自由电荷来源于杂质或弱电解质的 解离过程。在无外加电场或弱电场(小于 10 6 V/m，…”

Review on the History, Research, and Applications of Electrohydrodynamics

“…Aside from EHD micropumps using parallel planar and saw tooth-to-planar electrode designs, an EHD micropump with a parallel micropillar electrode design has also been presented, which displayed significantly increased performance, reaching a static pressure of 620 Pa with an applied voltage of 300 V and a 40-μm distance between the electrodes [166]. A more recent study of an EHD micropump, again with parallel planar electrodes and using HFE-7100 as the working fluid, displayed that a pressure head of 268 Pa is possible with only 90 V if the emitter electrode is made of gold instead of copper [167]. The same design with a copper electrode required over twice the voltage to produce the same performance.…”