A Comprehensive Framework for the Numerical Simulation of Evaporating Electrosprays

A framework for simulating the coupled physical phenomena that occur in evaporating electrosprays has been developed. This framework comprises a 3D Lagrangian model for droplets dynamics, evaporation, and Coulomb explosions, as well as steady-state 2D Eulerian models for gas flow induced by the droplets motions, the transports of vapor and heat in the gas phase, and the transport of the charged residues left behind by the fully evaporated droplets (residual-charge). To couple these different physics, the Lagrangian code and the four Eulerian ones are solved sequentially in order to attain a fully coupled solution of the global steady-state. This methodology has been applied to three electrospray systems made from solvents of different volatility (acetone, methanol, and n-heptane), with identical droplet size distribution at injection (a lognormal with mean diameter of 8 mm and CV D 10%). All fields converged after just a few (five) sequences of simulation. In the two systems in which the droplets travel fastest (acetone and methanol), conical fringes develop in the contour maps of volumetric rate of generation of residual-charge, which correspond to the first few Coulomb explosions. In the system in which the droplets moved slowest (n-heptane), such contour maps show an unstructured region, instead.