Study On CFD Numerical Simulation Of Mixing Characteristics And Light Regime In Tubular Photobioreactors

As the most widely used form of photobioreactors in large scale cultivation of energy microalgae, tubular photobioreactors urgently need to be optimized on the structure to improve mixing characteristics and light regime of microalgae. A novel tubular photobioreactor was systematically studied in this paper. The PIV test, CFD simulation, the structure optimization of static mixers and light regime of algal cells were carried out.First of all, the particle image velocimetry technology (PIV) and the CFD method were adopted to investigate flow fields of tubular photobioreactors with and without novel static mixers. The results showed that the novel static mixers could effectively enhance mixing degree of fluid. Compared with the PIV results, CFD results can accurately reflect the real fluid flowing, which showed the numerical methods based on the standard κ-ε model can well applied in the flow field simulation of tubular photobioreactors. The applicability and reliability of CFD simulation were verified.Then different static mixers were simulated and computed to compare their mixing characteristics, which showed the novel static mixer had the best mixing effect. Average velocity magnitude along the light direction (Uy), turbulent kinetic energy (TKE), pressure loss and average shear stress were regarded as main parameters to optimize the structure of the novel static mixer. The configurations including the cross angle of two blades of the static mixer a=90°, the horizontal spacing of adjacent static mixers s=80 mm, the open porosity of 16% and the hole radius r0=2 mm were considered to be appropriate.Lastly particle trajectories were simulated by combining particle tracking model with light attenuation model to study light regime. With novel static mixers, the light/dark cycle frequency was improved to increase by 85.21% and 95.77% at fluid inlet velocity of 0.3 and 0.4 m/s, respectively. The results showed the novel static mixers can effectively increase the light/dark cycle frequency of algal cells in tubular photobioreactors.