Scaling Effect on Micro Electrohydrodynamic Conduction Pump with Flush Electrode

Electrohydrodynamic (EHD) pumping is a promising method of generating fluid flow and pressure in fluid machinery, thermal control systems, and actuators. So, far, researchers have investigated micro-sized EHD pumps. However, the design method of conduction pumps, including electrode configuration, has yet to be determined. This study investigated the effects of electrode scale on EHD pumps of a similar shape with different scales to contribute to the pump design on a small scale. The pump consists of a rectangular channel with asymmetric flush electrodes. Three different sizes of 5 to 500 $\mu$m electrode gaps were used in the pumps of a similar shape. Fully coupled EHD simulations were performed using HFE 7100 as a working fluid. In this process, generated pressures were measured and compared with the experimental results of the EHD conduction pump fabricated using MEMS technologies. According to the numerical results, opposite polar heterocharge layers on each electrode were formed in all pumps. As the scale decreased, heterocharge layer area relative to the electrode gap increased. Overlap of positive and negative heterocharge layers was observed in the pumps with 5 and 50 $\mu$m electrode gaps. As the scale decreased, the relative overlap area increased, and the asymmetricity of heterocharge layers, which yields pressure generation and net flow by the pump, decreased. Despite the electrode length ratio of 1:3, the ratio of two heterocharge layer lengths for a 5 $\mu\mathrm{m}$ gap was found to be 1:1.1. These two findings should be considered when designing appropriate pump characteristics, particularly on a small scale $(\lt \mu$m).