Characterization and modeling of a microcapillary driven liquid–vapor phase-change membrane actuator

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 to 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 10.3 μm thick wicking structure and a 200 nm thick, 3 edge length silicon nitride actuation membrane was shown to demonstrate improved performance characteristics. The actuator generated peak pressures and deflections of 123 kPa and 167 μm when actuated with a 14.3 mJ heating pulse for a thermal efficiency of 0.15%.