[论文解读] Liquid soap film generates electricity

Ahmad Amjadi, Sadegh Feiz+1 more|arXiv (Cornell University)|May 30, 2013

Electrohydrodynamics and Fluid Dynamics参考文献 1被引用 5

一句话总结

本文展示了旋转的液态肥皂膜可作为电动发电机（LFEG）工作，通过电致流体动力力将机械旋转转化为电流。当在外部电场中旋转时，该薄膜能产生与角速度和外加电场成正比的可测量电压和电流，其结果与基于电致对流理论的数值模拟定性相符。

ABSTRACT

We have observed that a rotating liquid soap film generates electricity when placed between two non-contact electrodes with a sufficiently large potential difference. In our experiments suspended liquid film (water + soap film) is formed on the surface of a circular frame, which is forced to rotate in the $x-y$ horizontal plane by a motor. This system is located at the center of two capacitor-like vertical plates to apply an external electric voltage difference in the $x-$direction. The produced electric current is collected from the liquid film using two conducting electrodes that are separated in the $y-$direction. We previously reported that a liquid film in an external electric field rotates when an electric current passes through it, naming it the liquid film motor (LFM). In this paper we report a novel technique, in which a similar device can be used as an electric generator, converting the rotating mechanical energy to electrical energy. The liquid film electric generator (LFEG) is in stark contrast to the LFM, both of which could be designed similarly in very small scales like micro scales with different applications. Although the device is comparable to commercial electric motors or electric generators, there is a significant difference in their working principles. Usually in an electric motor or generator the magnetic field causes the driving force, while in a LFM or LFEG the Coulomb force is the driving force. This fact is also interesting from the Bio-science point of view and brings a similarity to bio motors. Here we have investigated the electrical characteristics of such a generator for the first time experimentally and modelled the phenomenon with electroconvection governing equations. A numerical simulation is performed using the local approximation for the charge-potential relation and results are in qualitative agreement with experiments.

研究动机与目标

• 研究旋转液态肥皂膜作为机械能转电能转换器的电学特性。
• 探索在微尺度水平下利用电致流体动力（EHD）力在薄液膜中发电的可行性。
• 基于电致对流控制方程，建立并验证描述该现象的理论模型。
• 将发电机行为与先前报道的液膜电机（LFM）进行对比，突出能量转换方向的差异。

提出的方法

• 在圆形框架上形成水与肥皂的悬浮液膜，并通过电机实现水平旋转。
• 通过两块垂直的电容式极板施加外部电场，使电场在x方向上呈横向分布。
• 使用两个沿y轴分离的非接触电极收集电流。
• 系统采用漏电介质模型和电致对流方程进行建模，对电荷-电势关系采用局域近似。
• 利用无量纲化的极坐标系控制方程进行数值模拟，求解不同角速度下的电势和电荷分布。
• 使用无量纲参数K = ωR²/(σα)表征系统，模拟针对不同转速对应的K值进行。

实验结果

研究问题

• RQ1 当受到外部电场作用时，旋转的液态肥皂膜是否能产生可测量的电流？
• RQ2 产生的电压和电流如何随薄膜的角速度和外部电场强度变化？
• RQ3 电致对流和表面电荷分布在此类液膜中实现能量转换的过程中起什么作用？
• RQ4 薄膜的电导率如何影响电能转换效率？
• RQ5 基于电致对流理论的数值模拟在多大程度上再现了实验观测结果？

主要发现

• 液态肥皂膜发电机（LFEG）产生的电压和电流与薄膜的角速度及外部电场强度成正比。
• 提高薄膜电导率会降低产生的电压，与电致对流理论预测一致。
• 数值模拟表明，在低角速度下，电势在y方向呈现与ω成正比的梯度，与实验观测相符。
• 随着角速度增加（K值增大），等势线开始随薄膜旋转，电荷密度因快速传导而降低。
• 在极高转速下（>5000 RPM），薄膜变得不稳定，限制了定量测量，但最大电压方向偏离90°的角度趋势与模拟结果一致。
• 基于简化刚体动力学和局域电荷-电势近似的模型，与实验结果表现出定性一致。