CFD analysis of the flow dynamics of microorganisms in dilute cultures in stirred tank photobioreactors

The objective of the present work is to investigate the influence of the key factors such as the impeller speed in revolutions per minute and frequency of crossover of the particles between the light and the dark zones on the growth of microalgae in a stirred tank photobioreactor. To that end, the numerical simulations are performed for the culture in a stirred tank photobioreactor using computational fluid dynamics. The culture medium and the sparged air are considered to be two interpenetrating continua. Based on the light intensity profiles within, the reactor is divided into light and dark zones. Individual microorganisms are tracked. The fractional time spent by them in the dark zone, and the average frequency of crossover between the zones, are determined. The critical impeller speed for the maximum cell growth is compared against the experimental observation reported in literature and the maximum tolerable shear stress is identified.