(359d) Simulations of Mixing and Radiative Interactions in Large-Scale Raceway Ponds for Algae Cultivation.

Understanding algae cultivation in raceway ponds is important for scaling up the growth of algae for many applications [1]. Among all the relevant variables affecting biomass growth in ponds, the degree of mixing and light penetration place at the top in terms of relative importance [2].

In this work, we simulate a 500 m² raceway pond for algae cultivation taking into account the dynamic interaction of algal cells with fluid flow and sunlight radiance. The fluid dynamics of the flows is simulated using the volume of fluid method (VOF), where the interface between the air and liquid phase is tracked and a single momentum equation to obtain the phase averaged velocity is solved [3]. This multiphase system is simulated using the open-source CFD software OpenFOAM [4]. Pond mixing is provided by a paddlewheel rotating between 10 – 15 RPM, which is simulated using a multi-reference frame method that imposes non-inertial frame momentum source terms in the vicinity of the paddlewheel. We validate our simulations with velocity measurements taken at different locations in the pond. We also study light availability as a function of depth which is one of the decisive factors in the overall algae growth and productivity. A set of radiation transport simulations are run in order to determine light availability as a function of concentration and depth. The objective is to obtain reduced order models (surrogate models) for light penetration, that along with the fluid dynamics will be coupled with an algae growth model.

[1] C. Inostroza, A. Solimeno, J. García, J. M. Fernández-Sevilla, F. G. Acién. Improvement of real-scale raceway bioreactors for microalgae production using Computational Fluid Dynamics (CFD) Algal Research 54 (2021) 102207

[2] J. Huang, X. Qu, M. Wan, J. Ying, Y. Li, F. Zhu, J. Wang, G. Shen, J. Chen, W. Li. Investigation on the performance of raceway ponds with internal structures by the means of CFD simulations and experiments. Algal Research 10 (2015) 64–71

[3] J. A. Heyns, and O. F. Oxtoby. Modelling surface tension dominated multiphase flows using the VOF approach. 6th European Conference on Computational Fluid Dynamics. 2014.

[4] S. S. Deshpande, L. Anumolu, M. F. Trujillo. Evaluating the performance of the two-phase flow solver interFoam. Computational science & discovery, 5(1), (2012) 014016.