Control of electrohydrodynamic (EHD) flow by secondary electric potential

Abstract

Non-thermal plasma (NTP) is generated around the surface of electrode where the electrons of gas molecules are excited by high external energy. Electrohydrodynamic (EHD) flow is produced by collision between electrically neutral molecules and positive ions emitted by ionization. Because of the characteristics of electrically driven flow, the NTP has been focused on for next generation application, and widely applied to industrial processes. However, most studies are limited to symmetric configuration to control the momentum of EHD flow. Hence, to better control that flow, secondary electric potential should be considered at the multi-electrode configuration, so that local enhancement of heat transfer can be observed. To date, EHD flow by asymmetric formation of the electric field has not been well researched or analyzed. In the present work, the symmetric configuration was firstly considered to obtain the reliability of EHD flow. Numerical simulation and experiments were carried out to validate the current, velocity profile, and Nusselt number. The particle image velocimetry (PIV) method was used to identify the velocity distribution of EHD flow. Also, the convective heat transfer induced by EHD flow could be analyzed. Secondly, the asymmetric configuration was considered by applying various magnitudes of secondary electric potential, which affected the momentum and direction of the EHD flow, which could be observed by the results of numerical simulation and the PIV method. To consider the application of heat transfer, it was verified that vertically controlled EHD flow could enhance local cooling performance, and showed increase of thermal efficiency. Through the visualization, it was noted that the ratio between main and secondary electric potential determined the extent of bias. Finally, the analytic model to predict the velocity profile could be proposed, and the regime map for the occurrence of reverse flow was presented.