Development of Microactuators Using Temperature Dependence of Surface Tension

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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.