Purification Mechanism of Submicron Aerosol in Microbubbles

The development of nuclear power is a critical component of the national energy strategy. However, across various stages of the nuclear power industry chain, radioactive aerosols that can enter the human body and cause internal exposure are widespread. Studies have shown that the threat posed by these aerosols to human health is inversely proportional to their particle size, with submicron-sized radioactive aerosols being the most hazardous. Due to limitations in previous detection technologies, the research and attention paid to such aerosols have been insufficient. Currently, pool scrubbing filtration technology is widely used in nuclear facilities to retain radioactive aerosols. This technology primarily generates millimeter-sized bubbles, which are less effective in purifying submicron aerosols in certain ranges, with purification efficiency as low as 20%. This presents significant safety risks, necessitating urgent research and improvement in more efficient purification methods. Based on the literature research, the smaller the bubble size, the better its retention effect on aerosols. Analyzing the behavior of bubbles of various sizes in water, micro-nano bubbles have the characteristics of stability, slow rising speed, and high mass transfer efficiency, which can be used to optimize the purification effect of traditional bubble washing. With the purification of sub-micrometer-sized aerosols as the background, this article proposed an aerosol purification method based on the generation of microbubbles. Based on the principles of hydrodynamic cavitation and turbulent fragmentation, a Venturi micro-nano bubble generator was used to produce micro-nano bubbles and generate negative pressure to aerosols. Heterogeneous condensation technology and ultrasonic atomization methods were used to generate nano and micrometer-sized aerosols. An integrated aerosol purification device was constructed, including a cylindrical water tank, a micro-nano bubble generator, an aerosol generator, a dust particle counter, and an air purification chamber. The size of the bubbles was captured using a high-speed camera combined with a bubble capture program, and the aerosol concentration was measured using a fast condensation particle counter and a laser dust particle counter. Experimental results demonstrate that the experimental setup can produce micro-bubbles with diameters ranging from 22 μm to 220 μm under an 8% gas content condition, achieving a 100% purification efficiency on aerosols larger than 1 μm, and exceeding a 99.96% total purification rate for aerosols smaller than 1 μm. With the experiment result, the mechanism of the purification was concluded. Initially, larger particles detach due to inertia and gravity, while smaller particles are influenced more by Brownian motion. Nano aerosols show slower initial purification but eventually reach high efficiency similar to full-sized aerosols. Experiments with specific particle sizes reveal that purification efficiency is sensitive to bubble size, especially for sub-micrometer aerosols. The system maintains over 99% efficiency in continuous and long-term purification, demonstrating its effectiveness in enclosed spaces. Microbubble methods can significantly improve traditional pond washing by enhancing purification efficiency and effectiveness.