Michael J. Debar

Fabrication and performance testing of a steady thermocapillary pump with no moving parts

Pumping in microdevices due to gradients in surface tension was investigated experimentally. Devices exhibiting the Marangoni effect in square channels were designed and fabricated from one silicon substrate and one quartz substrate. The two substrates were aligned, bonded and packaged for testing. Each of the devices consisted of a 100 /spl mu/m channel with three heaters along one of its sides. One heater generated a fluid-vapor interface while another controlled the temperature gradient along this interface. Flow could be generated in either direction, and could be switched on and off nearly instantaneously. Pressure was measured during device operation, and flow rate was measured indirectly through its proportionality to the time derivative of pressure in a quasi-steady flow. The devices were operated at a variety of heater settings to evaluate their performance over a range of flow rates and pressures. A minimum energy of 140 mW was required from the central heater to generate and maintain the vapor bubble, and the flow rate increased with input energy. The efficiency of the device increased with flow rate, since the overhead to create and maintain the bubble (140 mW) dwarfs the energy expended to generate the temperature gradient (15-50 mW). The devices generated a maximum pressure head of 44 Pa, and a maximum flow rate of 9.3 nL/s, although the maximum values did not occur simultaneously. In fact, the maximum pressure will always occur when the flow rate is zero, and vice versa.