Characterization of a Liquid-Vapor Phase-Change Actuator

Abstract

Factors affecting the efficiency of liquid-vapor phase-change actuators during dynamic operation are explored. To do this, a model actuator was specifically designed so that actuator geometry, material properties and operation could be easily varied in order to parametrically study their effects on actuator efficiency. A numerical model was developed so that the detailed energy budget within the device could be elucidated. It was found that device efficiency was maximized when the energy input into the actuator was equal to the energy required to dry out the evaporator. Membrane thermal mass and compliance, as well as the thickness of the evaporating liquid layer were also found to have a large impact on efficiency. In contrast, membrane thermal conductivity was found to have a minimal effect on efficiency for dynamic operation. Based on the parameter study, a liquid-vapor phase-change membrane actuator fabricated with a 10.3μm thick wicking structure and a 200nm thick 3mm-square silicon nitride actuation membrane was shown to demonstrate improved performance characteristics. The actuator generated peak pressures and deflections of 123kPa and 167μm when actuated with a 14.3mJ heating pulse for a thermal efficiency of 0.15%.