Modeling and Experimental Validation on The Ionic Strength and Charge Effect in Plasma-Induced Liquid Mobility

This study utilized a direct current-needle system for plasma generation and liquid flow inducement. The liquid flow was visualized and analyzed by Particle Image Velocimetry. The electrolyte solutions of Potassium chloride, Potassium bromide, Potassium iodide, Calcium chloride and Chromium(III) nitrate with concentrations ranging from 0.1 to 1.0 mM were studied. The results indicate that the plasma induces an upward liquid flow with an area mean velocity of up to 3.0 mm/s. The flow intensity decreases with increasing electrolyte concentration and shows a strong dependence on solution’s conductivity. A physical model is proposed for this particular finding. The plasma generates ions and electrons that shift the hydrogen bonds with water molecules, creating a surface tension gradient and the Marangoni effect. In contrast, the increase of solution’s conductivity shortens its Debye length which is the range of electric effect in liquid. Thus, the Marangoni stress and flow intensity decrease as the solution’s conductivity increases. Based on the regression analysis, the coefficient of determination is as high as 0.9365 showing that the flow intensity is significantly proportional to the square of the solution’s Debye length.