Numerical simulation on vortex flow and CO2 bubble aggregation behavior in a raceway pond with diaphragm aerators

• Published in: Biochemical engineering journal 2024-04, Vol.204, p.109243, Article 109243
• Main Authors: Zou, Xiangbo, Rao, Mumin, Ye, Ji, Kuang, Cao, Huang, Cong, Chen, Gongda, Qin, Shiwei, Song, Yanmei, Jia, Dongwei, Cheng, Jun
• Format: Article
• Language: English
• Subjects: Carbon neutrality; CFD simulation; CO2 fixation; Mass transfer; Microalgae
• ISSN: 1369-703X; 1873-295X
• DOI: 10.1016/j.bej.2024.109243

To optimize flow field in a raceway pond with diaphragm aerators to promote microalgal CO2 fixation, numerical simulation on three-phases (CO2 bubbles-culture medium-microalgae cells) with CFD (Computational Fluid Dynamics) - PBM (population balance model) was conducted to investigate effects of dynamic bubble aggregation/fragmentation on flow field distribution and mixing performance. The inhomogeneity of turbulent energy distribution increased with decreased bubble movement distance when inclination angle θ > 11º. When bubble generation diameter increased from 0.4 mm to 2.5 mm, average solution velocity and mixture turbulent kinetic energy first increased to peaks and then decreased, bubble aggregation height decreased and aggregation range became larger. When initial bubble velocity increased from 0.0314 m/s to 0.1257 m/s, microalgal flashlight frequency first increased to a peak of 0.47 Hz and then decreased, gas volume fraction and turbulent dissipation rate gradually increased. Finally, the growth rate of Chlorella increased by 22% to 0.71 g/L/d. [Display omitted] •Vortex pairs and trailing vortices appeared with an increased inclination angle θ.•Flow field and turbulent kinetic energy distribution are the most uniform at θ = 11°.•Average solution velocity increase first and then decrease with bubble diameter.•Flashlight frequency was the highest (0.47 Hz) when bubble velocity was 0.1 m/s.•Biomass growth rate increased by 22% to 0.71 g/L/d after optimization.