Electrospray beam currents in the cone-jet mode based on numerical simulation.

Electrospray technology is widely used in many technological areas. The beam current of electrospray is an important parameter since it directly associates with the electrohydrodynamic behavior of the cone jet and can be precisely measured. Although how the beam current changes with other variables has been theoretically and experimentally researched, the accurate prediction of the current is still difficult. Particularly, for liquids with high electrical conductivity, Ohmic conduction is a major component of the beam current, but it is ignored in many theoretical models. In this study, the beam current components are investigated via numerical simulation developed based on hydrodynamics and electrostatics equations. Consideration of both convection and conduction currents of the cone jet affords a more accurate calculation of the total beam current. Moreover, an interpolation method is employed to solve the charge "escape" problem, providing a more accurate calculation of charges as well as the currents. The results of the numerical model are validated against experimental results, showing good agreement regarding the meniscus shape and droplet diameters. For a highly conductive ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide (EMI-Im), the simulated beam current also shows good agreement with the experimental data, with a maximum error of 13%. Using the improved simulation model, temperature-induced beam current fluctuations are investigated to understand how an electrospray thruster behaves with temperature variations.