(550g) Bubble Column Void Fraction and Bubble Size Distribution

Bubble columns are widely used in the chemical industry. They are also used in the fermentation industry where microorganisms act like individual biorefineries and produce a desired product. Bubble column bioreactors are used because they have no moving parts, provide good heat and mass transfer characteristics, and can provide low-shear operation. Scale-up, however, continues to be a challenge. This work is part of a larger project to validate computational fluid dynamic (CFD) tools to better understand the interplay between bubble column bioreactor hydrodynamics and cellular metabolism. This presentation will address the first step in this work: void fraction and bubble size distribution measurements in a 32.1 cm diameter bubble column fitted with an eight-arm spider sparger. Initially, water is used to provide baseline data for CFD model validation. For the given geometry and sparger, void fraction measurements reveal a pure heterogenous flow over a range of superficial gas velocities of 1‑20 cm/s. Using a borescope and image analysis, a bimodal bubble size distribution is recorded at low superficial gas velocities, and the size distribution varies little throughout the bubble column. The bimodal bubble size distribution remains as the superficial gas velocity is increased.