Hydrodynamic constraints on the energy efficiency of droplet electricity generators

TL;DR

This paper analyzes hydrodynamic and electric factors limiting droplet electricity generator efficiency, revealing viscous dissipation as a major loss and proposing cascaded devices to improve energy extraction.

Contribution

It provides a theoretical framework identifying key hydrodynamic constraints and suggests design improvements for higher efficiency in droplet electricity generators.

Findings

Viscous dissipation accounts for up to 83% of energy loss.

Implication that cascaded devices could boost efficiency beyond 10%.

Identifies three main limits on current droplet electric generators.

Abstract

Electric energy generation from falling droplets has seen a hundred-fold rise in efficiency over the past year. However, even these newest devices can only extract a small portion of the droplet energy. In this paper, we theoretically investigate the contributions of hydrodynamic and electric losses in limiting the efficiency of droplet electricity generators (DEG). Noting that the electro-mechanical energy conversion occurs during the recoil that immediately follows droplet impact, we identify three limits on existing droplet electric generators: (i) the impingement velocity is limited in order to maintain the droplet integrity; (ii) much of droplet mechanical energy is squandered in overcoming viscous shear force with the substrate; (iii) insufficient electrical charge of the substrate. Of all these effects, we found that up to 83% of the total energy available was lost by viscous dissipation during spreading. Minimizing this loss by using cascaded DEG devices to reduce the droplet kinetic energy may increase future devices efficiency beyond 10%.