Application of Computational Fluid Dynamics in Optimizing Flat Plate microalgal Photobioreactor

Behnam Amanna

The sustainable production of microalgae holds great promise in addressing global challenges related to food security, bioenergy, and bioproducts. Arthrospira platensis (commonly known as Spirulina), a high-protein microalga, has gained considerable attention due to its nutritional profile and industrial versatility. Flat plate photobioreactors (PBRs) offer advantages over traditional open ponds, such as reduced contamination and higher productivity, but their operational efficiency requires careful design and optimization, particularly concerning mixing and light distribution. This thesis focuses on the integration of experimental cultivation and Computational Fluid Dynamics (CFD) modelling to optimize the design and operation of inclined flat plate PBRs for outdoor Spirulina cultivation. Here infrared-reflective film (IRF) flat plate PBRs were used for experimentation. Initial experimental work was conducted to gather reliable data for validating subsequent CFD models. Spirulina was cultivated across different seasons, and the impact of varying air injection flow rates (0.17–0.23 vvm) on effective quantum yield (f’q/f’m) and biomass productivity was systematically examined. Results from this phase demonstrated that excessive aeration induced physiological stress, while sub-optimal mixing led to decreased productivity. An optimal mixing rate of 0.21 vvm was identified for optimizing biomass yield and photosynthetic efficiency. To simulate and optimize the internal hydrodynamics of the PBRs, a validated CFD model was also developed. The model accurately predicted biomass productivity and fluid flow patterns across 20 scenarios involving different sparger positions and aeration rates. The results showed that a rear-positioned sparger at 0.21 vvm achieved comparable mixing performance to the center sparger at 0.23 vvm, with lower energy input and reduced dead zones. This finding has strong implications for energy-efficient design in large-scale algal systems. Building on this, further CFD investigations were conducted to explore the combined effects of baffle geometry and sparger location on fluid dynamics and biomass. Eighteen configurations were tested, involving three baffle heights, three opening sizes, and two sparger positions. The center sparger setup with low baffles and large openings (designated as Case C9) was identified as optimal, offering superior radial velocity, minimal dead zones, and enhanced mixing. These configurations significantly improved simulated productivity, providing concrete design recommendations for scalable systems. Complementing the computational and experimental work, a literature review provided a comprehensive evaluation of CFD methodologies in microalgal photobioreactor research. It highlighted the evolution of multiphase CFD approaches and their applications in optimizing light, mixing, and reactor geometries, setting the theoretical foundation for the work presented in this thesis. Together, these studies offer a holistic framework for the design and operation of flat plate PBRs through validated CFD modelling supported by empirical data. By identifying optimal configurations for mixing, sparging, and baffling, this research contributes to the advancement of energy-efficient and productive microalgal cultivation systems. The findings have practical implications for the commercial deployment of photobioreactor technology in nutraceutical, aquaculture, and bioenergy sectors.

Application of Computational Fluid Dynamics in Optimizing Flat Plate microalgal Photobioreactor

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