Numerical Simulation of Radiation Transport to Improve Microalgae Cultivation in an Air-Lift Photobioreactor

A comprehensive numerical model is developed to simulate the growth of microalgae under light/dark cycling conditions. The purpose of this study is to predict the growth rate of Chlorella vulgaris cultivated in photobioreactors (PBRs) in order to improve the light conditions for microalgae and enhance the photosynthetic efficiency. Computational fluid dynamics (CFD) is used to simulate its internal hydrodynamic behaviors. The Lagrangian method is employed to track the movement of microalgae cells. The radiative transfer equation (RTE) is used to obtain light intensity distribution. The combination of light radiation field and microalgae cell motions is used to construct the light history and they are integrated into the model of the photosynthetic units (PSU) to calculate the microalgae growth rate. The numerical results demonstrate that enhanced light/dark cycling frequency with ordered mixing can promote efficient microalgae cultivation. The effect of the vortex flow field generated by the baffles in an air-lift PBR is analyzed for increasing microalgae growth rate. When using the 1:1 baffle spacing, the biomass production of microalgae is increased by 41.8% compared to the original PBR.