Droplet Breakup Mechanism and Deposition Size Control in Non‐Contact Pneumatic Dispensing of a High‐Viscosity Shear‐Thinning Adhesive

ABSTRACT Stable breakup and deposition‐size control are important in localized dispensing of high‐viscosity shear‐thinning adhesives. A glutinous rice adhesive was characterized using the Carreau model, and a two‐dimensional axisymmetric VOF‐CSF model was established to simulate droplet formation and breakup, with high‐speed imaging used for qualitative and quantitative validation. After inlet‐velocity reversal, the nozzle‐side residual liquid retracted upward while the main droplet continued moving downward. This relative motion stretched the connecting filament and promoted local neck thinning until breakup. The normalized minimum neck radius followed a power‐law relationship with the normalized remaining breakup time, with an exponent of 0.266 ( R 2 = 0.990). The forward extrusion velocity had the strongest effect on deposited base diameter, whereas suction velocity and deceleration time showed weaker individual effects but contributed through parameter interactions. Response‐surface optimization identified a preferred parameter combination within the investigated range. Independent CFD validation gave a deposited base diameter of 1.98 mm and a deposited volume of 1.40 mm 3 . The results clarify the different roles of extrusion and suction in breakup and deposition‐size control during millimeter‐scale pneumatic dispensing.