Thermal-driven continuous kelvin water-drop generator for low-grade thermal energy harvesting

Effective harvesting and conversion of low-grade thermal energy into electricity are very important in sustainable energy development. The kelvin water-drop generator, which combines triboelectrification and electrostatic induction for charge generation, though proposed over a hundred years ago, it has not yet been applied for thermal power generation. This work proposes a thermally driven continuous kelvin water-drop generator that converts low-grade thermal energy into electricity via a self-sustained working fluid circulation. The system uses phase-change-mediated cycling to drive uninterrupted droplet electrification, thereby eliminating the external water supply requirement. Furthermore, to achieve better output performance, this work examines the effects of heating power, parallel capacitance, and storage device on the electrification process. When the optimized 22 nF parallel capacitor reaches equilibrium under 600 W heating conditions, the maximum accumulated charge reaches 4.96 nC, the voltage is 0.225 V, and the electrostatic energy is 0.546 nJ. It is worth noting that although the ion concentration decreases during thermal cycling, the charge accumulation can remain stable. The experimental results help to provide a clearer understanding of the electrification process in the kelvin water-drop generator. This work expands the application scenarios of kelvin water-drop generator and demonstrates its potential for low-grade thermal energy utilization.