Mechanisms and applications of reducing microbubble size via oscillatory gas supply: A comprehensive review

Oscillatory gas supply (OGS) has emerged as an effective method to enhance gas-liquid mass transfer in industrial applications by minimizing bubble size at submerged orifices. Compared to traditional steady gas supply (SGS), OGS facilitates premature bubble detachment from microporous diffusers, thereby reducing coalescence and enhancing transport phenomena. This improvement leads to lower energy consumption across sectors such as environmental engineering and chemical processing. This review critically examines the feasibility and applications of OGS in multiphase flow systems, including wastewater treatment, flotation separation, algae cultivation, and gas stripping. We first elucidate the mechanisms that contribute to bubble size reduction via OGS, followed by a comparative assessment of three technologies for generating oscillating airflow: solenoid valve, loudspeaker, and fluidic oscillator. Key factors influencing OGS performance, particularly oscillation frequency and amplitude, are discussed for their momentous role in producing smaller bubbles. Our findings demonstrate that OGS-generated microbubbles not only boost reaction efficiency and lower energy consumption but also reduce chemical usage and the footprint of treatment facilities. We conclude with insights and potential directions for advancing OGS technology, emphasizing that while enhancing gas-liquid mass transfer through OGS presents a promising approach, the development of stable oscillation-generating equipment is crucial for optimizing process performance.