Stirred tank reactors are widely used in industrial processes, including chemical processes like polymerization, biological processes such as cell culture and fermentation, pharmaceutical industry, and many other processes. Multiple impellers are usually preferred over single impeller for tall-thin configuration of industrial reactors for better gas utilization and maintenance of homogeneity in the reactor. In this work, the stirred tank reactor experimentally studied in Shewale and Pandit  is investigated numerically. The reactor is constituted by a cylindrical vessel with four baffles, and three impellers (one Rushton turbine, at the bottom of the tank, and two pitched blade turbines) mounted on the shaft and rotating synchronously.
A three-dimensional hexahedral mesh for the system is generated using a commercial mesh-generation software Pointwise®. CFD simulations are performed with the open-source CFD software OpenFOAM®. Steady state single-phase (liquid) simulations are performed with the realizable k-ε model, in order to describe the turbulence in the reactor. For gas-liquid system, a two-fluid model  with the mixture k-ε turbulence model  is used to solve the flow. The multiple reference frame approach  is applied for both systems to treat the rotation of impellers in the reactor. For both single phase and multiphase systems, the liquid phase is water at 300 K. And for multiphase system, air at 300 K is injected uniformly from the ring sparger located below the bottom Rushton turbine. Simulation results are compared to experiments reported in Shewale and Pandit , including flow patterns, unaerated and aerated power consumption, and overall gas holdup. The effects of different operating conditions such as impeller rotation speed at 3.75 rad/s and 5.08 rad/s are also studied.
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