Numerical Simulation of Cone-Jet Formation in Electrohydrodynamic Atomization

Electrohydrodynamic atomization (EHDA) process has received more research attention in recent years due to its potential to generate monodisperse droplets of low electric conductivity. It is reported that the EHDA process can be fine-tuned by adjusting the electrical field strength by an additional ring electrode near the nozzle tip to control both the spray mode and the droplet size. In the present study, a computational fluid dynamic (CFD)-based front tracking/finite volume method has been used to investigate numerically the effect of the secondary electric field source and the ring electrode on the EHDA process. The full Navier-Stokes equations are solved for both the liquid phase and the ambient air near the nozzle tip, and the liquid-air interface is monitored using a front tracking approach. At the interface, both the surface tension and the electrical stress due to surface charging and the applied electric field are taken into account. Because of the large dimension difference between the Taylor cone and the liquid jet, the simulations involve two drastically different length scales for describing the dynamic of the entire process. To accurately include the effect of the ring electrode, the electrical field distribution is first calculated over a domain large enough to enclose all key components of the EHDA process. Subsequently, the calculated electrical field in the large domain is integrated with the detailed CFD analysis on a small domain near the region of the nozzle tip. The formations of the Taylor cone, liquid jet, and droplets are successfully simulated and compared with experimental results with reasonable agreement. The numerical simulation method proposed in this article can be used as a platform for the investigation, analysis, and optimization of electrohydrodynamic atomization process. (C) 2010 American Institute of Chemical Engineers AIChE J, 57: 57-78, 2011