Water drops impact on a PVDF cantilever: droplet dynamics and voltage output

The effect of droplet dynamics on electric output of a PVDF (Polyvinylidene fluoride) cantilever is investigated through conducting in-laboratory experiments towards the raindrop energy harvesting (REH) applications. The droplet-substrate interaction affects the voltage output by several key factors, such as the droplet diameter, the impact velocity and the regime transition of droplet dynamics. The splash of droplet is shown to be dominant in voltage generation in an open circuit condition which is determined by the Weber number (We). The high-speed camera capturing technique allows the acquisition of both the droplet dynamic behaviors and the displacement of PVDF cantilever by means of which the effect on electric output can be comprehensively investigated. Results show that for single droplet impact, cantilever with a hydrophilic surface produces slightly higher voltage than that with a Super-hydrophobic (SH) surface; whereas for multiple droplet impacts, the SH surface performs better producing constant voltage amplitude and oscillating time. In this case, the accumulated water layer on hydrophilic surface attenuates the peak voltage successively especially when splash occurs. This work reveals the unneglectable effect of droplet dynamics on voltage output from an REH device. It may lay the foundation for improving energy conversion efficiency in terms of impact efficiency concerning the energy transfer from kinetic energy of droplet to vibration energy of a PVDF cantilever.