Droplet generation and evaporative cooling using micro piezoelectric actuators with ring-surrounded circular nozzles

Abstract

In this paper, we report a simple micro piezoelectric actuator aimed for droplet generation and evaporative cooling. A simple design of microfabrication and packaging mainly based on photolithographic techniques for the actuator was presented here. In particular, a low-cost microelectroforming process of nickel was employed for two types of metal nozzle plates with uniform-circular and ring-surrounded microstructures, in order to investigate the geometric influence of nozzles on cooling performances. Using the current piezoelectric actuators, the high volumetric rates (Vr) of water spray with 4.28---5.31 ml/min were successfully generated through a 5 × 5 array of nozzles fabricated with diameters ~30 μm each. Further, experimental results in cooling performance show that maximum cooling rates (Cr) of ?3.4 °C/min starting at ~38.5 °C was achieved within a housing space of 15 × 15 × 15 cm3. Moreover, both the values of Vr and Cr generated from the ring-surrounded nozzles were higher than those from the uniform-circular ones, thereby implying an `anti-stiction' mechanism caused by ring-shaped micro-channels. In the future, such an actuator featuring a low cost and high efficiency may find an cooling application as integrated in air conditioners and electric fans.