Characteristics of gel entrainment induced by gas recirculation in coaxial gas–liquid jets

Abstract

Jet entrainment has a significant impact on the performance and longevity of coaxial atomizers. This study aims to investigate the entrainment characteristics of fluids with different rheological properties under coaxial gas–liquid jets through rheological experiments and high-speed flow visualization techniques. As the airflow velocity increases, the liquid jet exhibits non-entrained, entrained, and over-entrained modes. We found that only in the over-entrained mode does the entrained fluid come into contact with the nozzle outlet. The transition conditions for each mode are determined and plotted in a dimensionless map of We-Oh. A “bulge” structure on the surface of the liquid column at the nozzle outlet was observed within a specific gas velocity range, and its formation mechanism and characteristics were investigated. Theoretical models for two critical gas velocities were obtained by analyzing “initial entrainment” and “full entrainment” states in recirculation zones using total pressure conservation theory. The proposed model demonstrates its applicability to three distinct fluid media, namely, guar gum gel, glycerol, and water, exhibiting excellent agreement with the corresponding experimental results.