Hydrodynamic and Heat Transfer Effects of Different Sparger Spacings Within a Column Photobioreactor Using Computational Fluid Dynamics

Abstract

An important factor in designing photobioreactors is appropriate selection of sparger geometry and placement. The sparger governs the bubble size distribution and gas hold-up. These factors in turn influence flow pattern, effective interfacial area, rates of mass transfer, heat transfer, and mixing. This project investigates the effects of sparger geometry and placement on bubble and fluid flow patterns and convective heat transfer within a column photobioreactor (PBR) using Computational Fluid Dynamics (CFD). Experimental and computational studies have been completed that focused on the hydrodynamics and heat transfer within a rectangular column photobioreactor (34.29 cm long × 15.25 cm wide × 34.29 cm tall) with a single sparger located at the center of its base (33.02 cm × 1.27 cm) running lengthwise. Similar studies have also been completed analyzing a full width sparger on the bottom of the PBR similar to a porous membrane sparger. This study extends previous work by investigating the flow patterns and heat transfer effects due to multiple rows of spargers at different spacings running perpendicular to the length of the PBR. Comparison of hydrodynamic and heat transfer parameters are made for the different types of spargers at different volumetric flow rates. The gas bubbles and the water-based media within the photobioreactor are modeled using the Lagrangian-Eulerian approach. A low Reynolds k-Epsilon turbulence model is used to predict near-wall flow patterns. The main interaction forces between the bubbles and the media, including drag forces, added mass forces, and lift forces, are considered. The overarching goal of this research is to improve PBR designs, thus enhancing microalgae production for biofuel and bioproducts production. It is hypothesized that changing the spacing of the PBR spargers will alter the bubble flow patterns. Despite its importance, optimizing the sparger geometry and placement in PBRs for microalgae production is still largely not understood. In this study, simulation results are presented for various sparger spacings, which can be helpful in designing sparger geometry and placement for maximized microalgae production.