Numerical simulation of sessile droplet evaporation enhanced by corona wind

Abstract

Sessile droplet evaporation under an electric field has become a promising cooling solution for high-power electronics, and the complicated heat transfer enhancement mechanism attracts much research attention. This study numerically investigated the effects of corona wind on the evaporation of sessile droplets. A needle-to-plate electrode configuration was employed, where the needle electrode was applied with high potential while the plate electrode was grounded. The relationships between the discharge properties, corona wind characteristics, droplet morphology evolution, internal Marangoni flow, temperature distribution, and vapor concentration were discussed. The results demonstrate that the accelerated ionized particles would generate an airflow from the needle electrode to the plate electrode, of which the maximum velocity was approximately 6.81 m/s with a + 20 kV applied electric potential. As a result, the lifetime of the evaporating droplets was found to significantly decrease from 228 s to 55 s. The internal Marangoni flow was strengthened by corona wind due to the interfacial cooling effects, whereas the shearing effects were rather negligible. In addition, the evaporating droplets with corona wind were likely to show a lower temperature than the neutral conditions, and the temperature distribution was highly dependent on the Marangoni flow pattern. In contrast, the shearing effects of corona wind would significantly increase the vapor concentration gradient, resulting in an improved evaporation rate. Finally, the local heat flux from hot substrates to the evaporating droplets was reported to be enhanced by the corona wind but with a low energy conversion efficiency of about 4.4 %. This work delivers crucial perspectives on the enhancement of sessile droplet evaporation.