Simulated cell trajectories in a stratified gas-liquid flow tubular photobioreactor

The fluid dynamic environment within a photobioreactor is critical for performance as it controls mass transfer of photosynthetic gases (CO2 and O2) and the mixing environment of the algal culture. At a cellular level, light fluctuation will occur when cells move between the “light”, well-illuminated volume of the culture near the light source and the “dark”, self-shaded zone of the culture. Controlled light/dark frequency may increase the light to biomass yield and prevent photoinhibition. Knowledge of cell trajectories within the reactor is therefore important to optimize culture performance. This study examines the cell trajectories and light/dark frequencies in a stratified gas–liquid flow tubular photobioreactor. Commercially available computational fluid dynamics software, ANSYS Fluent, was used to investigate cell trajectories within the half-full solar receivers at different liquid velocities and reactor tube diameters. In the standard configuration 96-mm solar receiver tube, the light/dark cycle frequencies ranged from 0.104 to 0.612 Hz over the liquid velocity range of 0.1 to 1 m s−1. In comparison, the smaller diameter 48- and 24-mm tubes exhibit higher light/dark frequencies, 0.219 to 1.30 Hz and 0.486 to 2.67 Hz, respectively