Alternatively permutated conic baffles generate vortex flow field to improve microalgal productivity in a raceway pond

- Alternatively permutated conic baffles were proposed to generate vortex flow field.
- Both clockwise vortexes were generated before and after baffles on vertical section.
- Horizontal self-rotary flow around baffles and vortex among baffles were generated.
- Bubble generation time and diameter decreased while bubble residence time increased.
- Biomass productivity of Spirulina increased 39.6% with baffles in a raceway pond.

Alternatively permutated conic (APC) baffles were proposed to generate vertical and horizontal vortex flow to intensify mixing and mass transfer in a raceway pond. Both clockwise vortexes were generated before and after conic baffles in the main stream to increase perpendicular velocity by 40.3% and vorticity magnitude by 1.7 times on vertical cross section. Self-rotary flow around conic baffles and vortex flow among conic baffles were generated to increase perpendicular velocity by 80.4% and vorticity magnitude by 4.2 times on horizontal cross section. The bubble generation time and diameter decreased by 25.5% and 38.7%, respectively, while bubble residence time increased by 84.3%. The solution mixing time decreased by 48.1% and mass transfer coefficient increased by 34.0% with optimized relative spacing (ε) and height (ω) of conic baffles. The biomass productivity of Spirulina increased by 39.6% under pure CO2 with APC baffles in a raceway pond.