An experimental investigation on cone-jet mode in electrohydrodynamic (EHD) atomization

Abstract

One of the most interesting spraying modes is cone-jet in which the meniscus takes on the form of a cone extended at its apex by a jet whose breakup gives rise to the fine drops. The choked, pulsating, and steady cone-jet in electrohydrodynamic (EHD) atomization were visualized by a high-speed digital camera with zoomed lens and stored to further analyze. The time evolution of cone or/and meniscus with applied potential, liquid flow rate and properties was conducted. The forces on the surface of meniscus are discussed to explore the deformation of liquid cone. The results indicate that the choked jet regime is found at very ‘low’ flow rate (usually smaller than minimum flow rate q0) and low applied potential (usually smaller than onset potential Φm), while the pulsating jet is observed at ‘high’ flow rate (slightly larger than minimum flow rate q0) and low applied potential (usually smaller than onset potential Φm). For a fixed liquid flow rate, a steady cone-jet occurs in a narrow range of applied potential for ethanol, while in a relatively broad range of applied voltage for diethylene glycol (DEG). The cone with different forms of convex, linear sides and concave in steady cone-jet mode was observed with an increase in applied potential for a fixed flow rate. The normal electric stress pushes the meniscus surface toward the capillary end and is balanced by the pressure due to viscous force stress, where the cone angle (drs/dz) is increased. The tangential stress drives the meniscus surface and makes the jet accelerate. Thus the cone undergoes the different forms of convex, linear sides and concave. The shape of cone is also affected by flow rate. The tip of cone is fat for ‘low’ flow rate, while sharp for ‘high’ flow rate. Meanwhile, a jet ejected from the tip of the cone becomes longer and thicker with an increase in flow rate. Thus it increases the flow rate to ensure the constant volume of the cone for ‘high’ flow rate. The properties of liquid also affect the shape of the cone. In addition, a pulsating cone-jet is conducted and the effect of operating parameters and liquid properties is discussed. The dimensionless diameter as a function of the dimensionless flow rate is good accordance with scaling laws.