Simulation of Electrospray Emission Processes for Highly Conductive Liquids

TL;DR

This paper develops and validates a numerical model to simulate electrospray emission of highly conductive liquids, revealing how fluid properties and flow conditions influence droplet charge and shape.

Contribution

It introduces a comprehensive electrohydrodynamic model incorporating charge relaxation and validates it against experiments for high conductivity liquids.

Findings

High conductivity leads to higher droplet charge-to-mass ratios.

Convex cone shapes are associated with high conductivity and surface tension.

Recirculation flows indicate instability onset at minimal stable flow rates.

Abstract

An electrohydrodynamic numerical model is used to explore the electrospray emission behavior of both moderate and high electrical conductivity liquids under electrospray conditions. The Volume-of-Fluid method, incorporating a leaky-dielectric model with a charge relaxation consideration, is used to conserve charge to accurately model cone-jet formation and droplet breakup. The model is validated against experiments and agrees well with both droplet diameters and charge-to-mass ratio of emitted progeny droplets. The model examines operating conditions such as flow rate and voltage, with fluid properties also considered, such as surface tension, electrical conductivity, and viscosity for both moderate and high conductivity. For high conductivity and surface tension, the results show that high charge concentration along with the meniscus and convex cone shape results in a higher charge-to-mass ratio of the emitted droplets while lower conductivity and surface tension tend towards concave cone shapes and lower charge-to-mass droplets. Recirculation flows inside the bulk liquid are investigated across a range of non-dimensional flow rates, and electric Reynolds numbers. For high conductivity liquid emission at the minimum stable flow rate, additional recirculation cells develop near the cone tip suggesting the onset of the axisymmetric instability.