Development of Microactuators Using Temperature Dependence of Surface Tension

众所周知，在微机电系统（MEMS）的尺寸中，表面力比体积力更普遍。这是因为前者与长度尺度的平方幂成正比，而后者与三次方成正比。因此，我们提出了一种新型的表面张力驱动的微泵系统，即利用热电元件作为温度控制器的马兰戈尼效应。我们将热电元件分布在通道内，并在元件之间捕获适量的气体;元件之间形成的气液界面是泵浦功率的来源。每个热电元件具有根据珀耳帖效应吸收和释放热量的两个结。由于从这些结到工作液体的热传递沿气-液界面施加了沿着温度梯度，因此由Marangoni效应引起从热-液侧到冷-液侧的流动。为了促进流动，许多热电元件沿着流动回路分布。该系统的特征如下：-该系统不包含任何可移动部件，并且具有非常简单的结构。- 与容积式泵不同，没有流量脉动。- 对于EHD泵中遇到的工作液体的电导率没有限制。- 通过施加在热电元件上的电压可以容易地控制流量。作为微泵系统的基础研究，考虑热电元件的电学特性，对微泵系统的二维温度场和流场进行了数值模拟。此外，我们尝试制造几个微型泵，但操作不成功，因为气-液界面的变形诱导的自由对流驱动的意想不到的漩涡。然而，目前正在进行基于微制造技术的进一步试验。

As is widely known, in the dimensions of micro electro mechanical systems (MEMS), surface forces are much more prevalent than body forces. This is because the former are proportional to the square power of length scales, while the latter are proportional to the cubic power.Therefore, we propose a new type of micropump system driven by surface tension, namely, the Marangoni effect using thermoelectric elements as temperature controllers. We distribute thermoelectric elements inside a channel, and trap an appropriate amount of gas between the elements ; the gas-liquid interfaces formed between the elements are the source of the pumping power. Each thermoelectric element has two junctions which absorb and discharge heat according to the Peltier effect. Since heat transfer from these junctions to the working liquid imposes temperature gradients along the gas-liquid interfaces, the flow from the hot-liquid side to the cold-liquid one is induced by the Marangoni effect. In order to boost the flow, many thermoelectric elements are distributed along the flow circuit. The features of this system are as follows : - The system does not contain any movable parts, and has a very simple structure. - There is no flow pulsation unlike the positive displacement pump. - There is no limitation on the electrical conductivity of the working liquid as encountered in EHD pumps. - Flow is easily controlled by the electric voltage applied to the thermoelectric elements. As a basic study of the present micropump system, a numerical simulation was made for twodimensional temperature and flow fields taking the electrical characteristics of the thermoelectric elements into account. Also, we tried to manufacture several micropumps, but operations were not successful because the deformation of gas-liquid interface induced unexpected eddies driven by free convection. However, a further trial based on micro fabrication techniques is currently in progress.