Numerical simulations and validation of single- and two-phase flow in a stirred lab-scale photobioreactor

A particle image velocimetry (PIV) technique was used to measure velocity fields of single- and multi-phase fluid flow in a stirred, flat-panel photobioreactor and to validate the computational fluid dynamics (CFD) model. The paper presents the grid independence study, velocity profiles, and shear stresses that were studied under four different operating conditions, i.e. two different agitation speeds, 360 rpm, and 480 rpm, and with or without aeration of 200 ml min(-1). The single-phase numerical model showed a correlation in the improved accuracy, and the mesh refinement, even though using a very fine mesh, did not justify the increased computational costs, making a medium mesh more practical. Similarly, the two-phase flow analyses showed a good qualitative agreement with the PIV data. However, PIV measurement in bubbly flows is a challenging task, possibly having large uncertainties due to light effects at the gaseliquid interface. Nevertheless, the large vortex formed near the rotating magnetic stirrer was found to dominate the flow pattern in both, single- and multi-phase, simulations. The effect of the aeration on shear stresses was, naturally, more noticeable with lower agitation speeds. However, with both agitation speeds, the highest shear stresses around the stir bar were found to quickly decay. Thus, the environment in the photobioreactor can be considered appropriate for the cultivation of microalgae. (c) 2023 IAgrE. Published by Elsevier Ltd. All rights reserved.