Session: 04-07-02: Interfacial Phenomena and Flows

Paper Number: 130358

130358 - Characterizing Air Entrainment at the Gas-Liquid Interface in Stirred Tank Reactors 

Air entrainment, also known as surface aeration, is common when the shear between a gas region and liquid region is significant. Air entrainment is found in wind-driven flows, at the gas-liquid interface of mixing systems and small and large scale fermentation tanks. This gas-liquid mixing forms a multiphase flow, and either promotes the separation of low-density components in a mixture or increases oxidation, both of which could disrupt the yield of a fermentation process. This study utilizes a standard stirred tank reactor (STR) equipped with a Rushton disc turbine impeller and baffles to examine air entrainment at the gas-liquid interface. High-speed backlit imaging is employed to visualize and characterize the air entrainment. The impeller speed and the distance between the impeller and the static liquid height significantly impact the amount of air drawn into the system. Substantial surface deformation is observed, which is a function of impeller speed and location, and leads to different surface aeration flow regimes. Flow regime identification is also influenced by how the surface fluctuations interact with the STR baffles. A flow regime map is[AP1]  proposed for various impeller speeds and locations. Methods to quantify void fraction due to surface aeration and relate it to the different flow regimes will be outlined and will be the focus of future work.

Presenting Author: Mohammed Y. Al-Subaey Iowa State University