Building water bridges in air: Electrohydrodynamics of the Floating Water Bridge

TL;DR

This paper explores the electrohydrodynamics of the floating water bridge, demonstrating how electrical fields can stabilize a water thread between beakers and analyzing the forces and charges involved.

Contribution

It presents experimental measurements and simple models that explain the stability and flow mechanisms of the floating water bridge, highlighting polarization forces and free charge effects.

Findings

Polarization forces are crucial for bridge stability.

Flow is driven by free surface charges.

The water bridge can be modeled as a leaky dielectric liquid.

Abstract

The interaction of electrical fields and liquids can lead to phenomena that defies intuition. Some famous examples can be found in Electrohydrodynamics as Taylor cones, whipping jets or non-coalescing drops. A less famous example is the Floating Water Bridge: a slender thread of water held between two glass beakers in which a high voltage difference is applied. Surprisingly, the water bridge defies gravity even when the beakers are separated at distances up to 2 cm. In the presentation, experimental measurements and simple models are proposed and discussed for the stability of the bridge and the source of the flow, revealing an important role of polarization forces on the stability of the water bridge. On the other hand, the observed flow can only be explained due to the non negligible free charge present in the surface. In this sense, the Floating Water Bridge can be considered as an extreme case of a leaky dielectric liquid (J. R. Melcher and G. I. Taylor, Annu. Rev. Fluid Mech., 1:111, 1969).