Understanding electrohydrodynamic (EHD) performance of corona discharge via particle image velocimetry (PIV)

Abstract

Electrohydrodynamic (EHD) pumping through corona discharge has found many interesting applications, as it does not require any mechanical moving parts. However, understanding the EHD performance of the corona discharge is crucial for a controllable manipulation of the fluids. This study investigates the pumping performance of an in-house built corona discharge setup for inducing circular motions in the fluids. Silicone oils of different kinematic viscosities are used as the EHD fluid. The EHD performance/fluid characteristics are studied experimentally using particle image velocimetry (PIV) under different DC corona voltages and their results are verified using the continuity equation. Additionally, an analytical model is derived using the Navier–Stokes equations. A clear scaling effect of the corona voltage is seen for the EHD fluid. The EHD fluid exhibits higher velocities at high corona voltages with low perturbation frequency ($$< 3$$ < 3 Hz) which is attributed to a sloshing motion in the fluid. This naturally occurring sloshing (out-of-plane) motion can be utilized when mixing is desired in the fluid. The results of this study can be used for contact-less and controllable manipulation of dielectric fluids (i.e., silicone oils) for potential applications in emulsion formation and separation. Graphical abstract

Impact of Processing Parameters on Contactless Emulsification via Corona Discharge

“…Under given corona operating parameters, an increase in oil viscosity leads to a decrease in the circulation velocity of the oil. In a separate study, we showed that Reynolds number vs corona voltage follows a power-law trend . In this study, it was found that in order to achieve different EHD-induced motions in the oil medium, different voltages as well as different oil viscosities should be utilized .…”

“…When a non-conductive medium (i.e., silicone oil) is placed between the corona generating and ground electrodes, a nonuniform electric field forms within the medium that can lead to its pumping and/or deformation depending on various processing parameters (i.e., h, L, V, and t). 36,45,53 For electroemulsification purposes via corona discharge, it is important to achieve efficient EHD pumping of silicone oil without its deformation, which is typically known as Taylor cone formation. 35,103 The deep deformations in the nonconductive silicone oil mostly occur due to extreme EHD forces that appear under certain processing conditions such as very low distance between the two electrodes (L and h), low depth of the silicone oil (t), very high corona voltages (V), etc.…”

“…In a separate study, we showed that Reynolds number vs corona voltage follows a power-law trend. 52 In this study, it was found that in order to achieve different EHD-induced motions in the oil medium, different voltages as well as different oil viscosities should be utilized. 53 Lower oil viscosities facilitate penetration and diffusion of the charged water droplets since they have nearly the same value for surface tension while showing less viscous resistance.…”

“…52 In this study, it was found that in order to achieve different EHD-induced motions in the oil medium, different voltages as well as different oil viscosities should be utilized. 53 Lower oil viscosities facilitate penetration and diffusion of the charged water droplets since they have nearly the same value for surface tension while showing less viscous resistance. 54−56 Figure 2A shows the size of the water droplets in W/O emulsions formed under DC corona discharge of V = +10 kV and processing conditions of h = 15 mm, L = 20 mm, and t = 8 mm for silicone oils with different viscosities.…”