Interaction and Transport of Liquid Droplets in Atmospheric Pressure Plasmas (APPs)

Abstract

The transport of liquid droplets in atmospheric pressure plasma (APP) has been recognized as a two-phase flow. The liquid droplet introduces a perturbation in APP and under several constraints, the behavior of this perturbation is not clear during transport. As soon as the droplets interact with the APP, they become charged, which causes the droplets to evaporate. Using 1D normalized fluid model, we first describe how the liquid droplets charge and interact with helium APP. The impact of this droplet-plasma interaction is then discussed and described using 2D coupled fluid-droplet model. The numerical modeling outcomes suggested that the evaporation of droplets has emerged as a primary mechanism in plasma; however, the mutual interactions, such as grazing and coalescence between the droplets, are dominant at higher precursor flow rates (>100 μl min−1). To demonstrate the importance of different liquid precursors during droplet-plasma interaction, we analyzed the spatiotemporal patterns of discharge plasma while considering the effects of HMDSO, n-hexane, TEOS, and water. Variable gas and liquid precursor flow rates are used to further examine the features of discharge plasma. Comparing penning ionization to other ionization processes, it is found to be the prime activity along the pulse of droplets, demonstrating the significance of small nitrogen impurities. Using a laser diffraction particle size analysis approach as part of an APP jet deposition system, the validation of the numerical simulations is proven by comparison with experimental observations of droplet size distributions.