Investigation On Fluid Hydrodynamic And Structure Optimization Of Open Raceway Pond

Photobioreactor (PBR) as the key devices for Microalgae photoautotrophic cultivation is essential for large-scale cultivation of microalgae. The open raceway pond (RWP) is the most widely used PBR for microalgae cultivation, and its structures are urgent to be optimized so as to improve the efficiency of microalgae cultivation and reduce the energy consumption.In this paper, fluid hydrodynamic characteristics and structures of the raceway pond were investigated and optimized using the Computational Fluid Dynamics (CFD) technology. And then simulation results were validated by the photoautotrophic and photoinduction cultivation of Chlorellapyrenoidosa. The main contents and results are as follows:(1) The RWPs with different configurations of bend (semicircular flow deflectors, deflectors of pier, island configuration, traditional bend), different structures of bottom (horizontal and inclined), different number of paddlewheels (one and two) and different ratio of length and width were simulated by CFD. It can be found that the RWPs with semicircular flow deflectors, horizontal bottom, two paddlewheels and the ratio of length and width of two are better than others by comparing the average fluid velocity, percentage of dead zones and velocity along the light direction at the condition of the same power.(2) In order to improve the fluid velocity along the direction of light which is the most critical parameter, a structure of sloping baffles were developed. Sloping baffles and flow deflectors fitted in the RWP can increase the average fluid velocity and reduce the dead zones, and more importantly, can obviously improve the fluid velocity along the direction of light and reduce the light/dark cycle. The sloping baffles were then optimized and applied to different area of RWPs which are80m2and20m2. And the fluid velocities along the direction of light in both of the two RWPs were apparently increased.(3) Some of the simulation results were verified by the experiment of photoinduction and photoautotrophic cultivation of Chlorella pyrenoidosa, including the RWPs with deflectors of pier, flow deflectors and sloping baffles. Cultivation results were consistent with the simulation results, which further illustrate the adaptability and reliability of the CFD simulation and the evaluation parameters.