Analysis of rising motion characteristics of microbubbles in a heated quiescent salt solution

Abstract

Microbubbles hold promising potential in applications across fields such as wastewater treatment, chemical reactions, and the nuclear industry. In this study, we analyzed the trend of microbubble rising velocity using a high-resolution high-speed camera in a sodium sulfate solution at 60 °C and found that the rising velocity trend is non-monotonic. The efficient mass transfer capability of microbubbles led to diameter reduction during ascent, which in turn influenced the rising velocity. The microbubble rising motion was divided into three stages: initial acceleration, deceleration, and secondary acceleration. Stokes' law and its modified formulas did not fully predict the rising velocity observed experimentally, showing accuracy only at the early stage of the secondary acceleration phase. This study interprets the velocity variation from the perspective of diameter fluctuation during microbubble ascent, elucidating the applicability of Stokes' law for microbubbles in 60 °C saline solution. By performing power correction on Stokes' law, the prediction accuracy was improved, and the velocity data of microbubbles during the secondary acceleration stage fell within the prediction interval with 90 % confidence. Additionally, microbubble collision and aggregation events were observed during the experiments; however, they were rare (less than 0.01 %) and had negligible effects on the statistical data of microbubble motion velocity.