A micropump driven by the thermocapillary convection is proposed. The purpose of this study is to elucidate the flow structure in liquid region and the effect of the geometry on the performance of the present micropump. There are two significant advantages in the thermocapillary-driven system. First, the surface forces become more dominant than the volume forces with decreasing scale. The present micropump driven by the surface forces shows an advantage in the micro scale over a diaphragm pump driven by the volume forces. Secondary, the thermocapillary driven system contains no movable parts; thus, it allows a very simple structure compared to the diaphragm one. In the present micropump system, a number of ribs are distributed along the flow circuit between a heater and a cooler (see Fig. A-1). An appropriate amount of gas is trapped between the ribs; the gas-liquid interfaces formed between the ribs are the source of the pumping power. Since heat transfer from these ribs to the working liquid imposes temperature gradients along the gas-liquid interfaces, the flow from the hot to the cold side is induced by the Marangoni effect. Fundamental characteristics of the present micropump are studied on the basis of three-dimensional simulation conducted taking the gas, liquid and ribs into account. Since the surface tension is controlled by the temperature of the ribs, the equations for liquid and gas phases are formulated by coupling them with the heat conduction equation for the ribs. The intensity of the flow induced by the thermocapillary force can be described by using the Marangoni number. In this study, the flow structure corresponding to the temperature field was observed (see Fig. A-2). Since the high temperature fluid is convected downstream, the temperature of the central liquid region exceeds the temperature of the ribs at the same streamwise position. Therefore, the flow from the central field to the ribs is induced by the Marangoni effect on the gas-liquid interfaces. The present calculation has revealed that the flow field exhibits a transition from steady flow to oscillatory flow when the Marangoni number exceeds a critical value of about 2,000 – 2,500. An experiment was also performed. The liquid flow driven by the present micropump system was confirmed through the experiment.

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