Simulation Method Linking Dense Microalgal Culture Spectral Properties in the 400-750 nm Range to the Physiology of the Cells

Prediction of radiative properties of spherical microalgae considering internal heterogeneity and optical constants of various components

Most of the current predictions of the radiative properties of microalgae use the homogeneous sphere approximation based on the Mie scattering theory, and the refractive indices of the model were regarded as fixed values. Using the recently measured optical constants of various microalgae components, we propose a spherical heterogeneous model for spherical microalgae. The optical constants of the heterogeneous model were characterized by the measured optical constants of microalgae components for the first time. The radiative properties of the heterogeneous sphere were calculated using the T-matrix method and were well verified by measurements. It shows that the internal microstructure has a more significant effect on scattering cross-section and scattering phase function than absorption cross-section. Compared with the traditional homogeneous models selected with fixed values as refractive index, the calculation accuracy of scattering cross-section of the heterogeneous model improved by 15%-150%. The scattering phase function of the heterogeneous sphere approximation agreed better with measurements than the homogeneous models due to the more detailed description of the internal microstructure. It can be concluded that considering the internal microstructure of microalgae and characterizing the microstructure of the model by the optical constants of the microalgae components helps to reduce the error caused by the simplification of the actual cell.

Modeling and Simulation of Photobioreactors with Computational Fluid Dynamics—A Comprehensive Review

Computational Fluid Dynamics (CFD) have been frequently applied to model the growth conditions in photobioreactors, which are affected in a complex way by multiple, interacting physical processes. We review common photobioreactor types and discuss the processes occurring therein as well as how these processes have been considered in previous CFD models. The analysis reveals that CFD models of photobioreactors do often not consider state-of-the-art modeling approaches. As a comprehensive photobioreactor model consists of several sub-models, we review the most relevant models for the simulation of fluid flows, light propagation, heat and mass transfer and growth kinetics as well as state-of-the-art models for turbulence and interphase forces, revealing their strength and deficiencies. In addition, we review the population balance equation, breakage and coalescence models and discretization methods since the predicted bubble size distribution critically depends on them. This comprehensive overview of the available models provides a unique toolbox for generating CFD models of photobioreactors. Directions future research should take are also discussed, mainly consisting of an extensive experimental validation of the single models for specific photobioreactor geometries, as well as more complete and sophisticated integrated models by virtue of the constant increase of the computational capacity.