Active New Microvalve Based on Phase Change Effect

In this work we will show a new type of a microvalve that uses the phase change effect in order to control the flow of a fluid. The valve consists just of a micro channel that possesses a heating element made of copper at one side. Furthermore, the valve can be cooled by a special external cooling system. If the fluid flowing trough the channel gets a temperature below the phase transition temperature it becomes a solid. The flow of the former fluid will be stopped. By means of an electrical current applied on the heating element the flow can be restored. We have investigated in this work the flow of melted wax. The melting temperature is above 80°C. The viscosity of the wax changes from 50mPas at 80°C to 3mPas at 140°C. We investigated new microvalves with channel dimensions between 20 mm and 90 mm in diameter. Two types of the channels, with circled and elliptical shaped cross-section, have been studied, too. The wax temperature varies from 80°C to 140°C. A cooling fluid that possesses a temperature of 20°C cooled the valve. The time constant of cooling and flow stopping depends on the material of the channel, the fluid temperature and the channel geometry. It can vary between 30ms to 120ms. Technological procedures for production of such one he new microvalve can be produced by means of silicon microtechnologies.