Numerical study on the effects of fluid properties in electrohydrodynamic pulsating jet under constant voltage

TL;DR

This study uses numerical simulations to analyze how different fluid properties influence the behavior and regimes of electrohydrodynamic pulsating jets, providing insights into controlling jet stability in printing applications.

Contribution

The paper introduces a numerical model that identifies key dimensionless parameters governing pulsating jet regimes based on fluid properties, enhancing understanding of jet dynamics in EHDP.

Findings

Three ejection regimes identified: oscillating cone, choked jet, stable cone-jet.

Liquid viscosity and conductivity significantly influence jet oscillation and transition.

Viscous force dominates in high viscosity liquids, affecting jet stability.

Abstract

Pulsating jet is one of the common working modes in electrohydrodynamic printing (EHDP) that process is highly affected by operating parameters and material properties. In this paper, the processes of pulsating jet for liquids with different physical properties were investigated using numerical simulation. An electrohydrodynamic solver was established, and a charge flux restricting step was adopted to ensure a realistic distribution of free charges. Three various ejection regimes were observed in our simulations: oscillating cone (OC), choked jet (CJ), and stable cone-jet (SJ). We found that three dimensionless numbers relating to liquid properties determined the ejection regime: the Ohnesorge number, Q0{\epsilon}r/Q, and Q0/(QRe). Based on those dimensionless numbers, the roles of liquid properties on pulsating jet (OC and CJ) were analyzed. In OC, the break of the jet is due to the significant oscillation of the Taylor cone, which is mainly affected by viscosity and conductivity. In CJ, the jet emission is terminated by the excessive resistant force in the cone-jet transition region. For liquids with low and medium viscosity, the dominant resistant force is the polarization force or viscous force when {\epsilon}rRe is larger or smaller than 1, respectively. For high viscosity liquids, the viscous force always becomes the major resistance. These results further reveal the physical mechanism of pulsating jet and can be used to guide its application.