Computational and Experimental Investigation of Bubble Circulation Patterns Within a Column Photobioreactor

Abstract

This research project investigates bubble and liquid circulation patterns in a vertical column photobioreactor (PBR) both experimentally as well as computationally using Computational Fluid Dynamics (CFD). Dispersed gas–liquid flow in the rectangular bubble column PBR are modeled using Eulerian–Lagrangian approach. A low Reynolds number k–ε CFD model is used to describe the flow pattern near the wall. Bubble size distribution measurements are carried out using a high-speed digital camera. A flat surface bubble column PBR is used to achieve sufficient light penetration into the system. Carbon dioxide, which is necessary for photosynthetic microalgae growth, is added to the sparged air. The results are validated with experimental data and from current literature. Design parameters, bubble flow pattern and internal hydrodynamics of a bubble column reactor were studied and the numerical simulations presented for the hydrodynamics in a bubble column PBR account for bubble phenomena that have not been sufficiently accounted for in previous research. Bubble size and shape affect the hydrodynamics as does bubble interaction with other bubbles (multiple bubbles in a flow versus single bubbles and wall effects on bubble(s) which are not symmetrical or bubbles not centered on the reactor cross-section). Understanding the bubble movement patterns will aid in predicting other design parameters like mass transfer (bubble to liquid and liquid to bubble), heat transfer (within the PBR and between the PBR and environment surrounding the PBR), and interaction forces inside the PBR.