2024/05/20 by Mizuki Kato, Kyoko Namura, Kato, Mizuki +9
Engineering · Environmental Science · #FOS: Physical sciences #Fluid Dynamics (physics.flu-dyn) #Fluid Dynamics and Mixing #Minerals Flotation and Separation Techniques
paper · doi:10.48550/arxiv.2405.11731
openalex publication_date 2024/05/20 · openalex created_date 2024/05/22 · openalex updated_date 2026/07/28
This study investigates the behavior of microbubbles generated by the local heating of an ethanol/water mixture and the surrounding flow. The mixture is photothermally heated by focusing a continuous-wave laser on a FeSi2 thin film. Although the liquid is not degassed, vapor-rich bubbles are stably generated in an ethanol concentration range of 1.5-50 wt% The vapor-rich bubbles absorb the air dissolved in the surrounding liquid and exhale it continuously as air-rich bubbles ∼ 1 μm in diameter. For the same ethanol concentration range, the solutal-Marangoni force becomes dominant relative to the thermal-Marangoni force, and the air-rich bubbles are pushed away from the high-temperature region in the fluid toward the low-temperature region. Further, it was experimentally demonstrated that Marangoni forces do not significantly affect the surface of vapor-rich bubbles generated in ethanol/water mixtures, and they produce a flow from the high-temperature to the low-temperature region on the vapor-rich bubbles, which moves the exhaled air-rich bubbles away from the vapor-rich bubbles near the heat source. These effects prevent the vapor-rich and exhaled air-rich bubbles from recombining, thereby resulting in the long-term stability of the former. Moreover, the flow produced by the vapor-rich bubbles in the non-degassed 0-20 wt% ethanol/water mixture was stronger than that in degassed water. The maximum flow speed is achieved for an ethanol concentration of 5 wt%, which is 6-11 times higher than that when degassed water is utilized. The ethanol/water mixture produces vapor-rich bubbles without a degassing liquid and enhances the flow speed generated by the vapor-rich bubbles. This flow is expected to apply to driving and mixing microfluids.