Experimental Investigation of Temperature Effects on Breakup Mechanisms of Supercritical-Assisted Atomization

Supercritical CO₂ is proved as an excellent choice in supercritical-assisted atomization (SAA) systems. The sensitivity of SAA to operational conditions and properties of injected mixture enables practical customization. Since the rheological properties of supercritical fluids strongly depend on temperature, the breakup mechanism is significantly affected by crossing the critical temperature. Here, we experimentally investigate the breakup mechanism of CO₂-assisted atomization (CO₂-A) at subcritical, critical, and supercritical states and compare it with cases where N₂ is utilized as the assisting fluid at the same conditions. High-speed imaging and laser diffraction are used to analyze the evolution of the liquid jet during the primary and secondary atomization processes. The primary breakup of CO₂-A is found to be the emergence, expansion, and burst of CO₂ bubbles and formation of ligaments that break up into small droplets, due to the high solubility of CO₂ in water and low interfacial tension of the CO₂-water mixture.