Aeration and mass transfer


In industrial process engineering, aeration is a vital unit operation that involves the uniform dispersion of the gas phase into the liquid phase, maximizing mass transfer (absorption or desorption). Absorbing gas into a liquid to trigger a chemical reaction is often a critical responsibility. Occasionally, the gas simply provides energy via buoyancy for mixing the liquid. Aeration in reactors plays an essential role in many processes across the water treatment, chemical, pharmaceutical, and biotechnology industries.
By employing CFD simulations, we can analyze crucial process parameters, such as:

  • Gas distribution throughout the system
  • Total gas hold-up
  • Mass transfer rate
  • Mass transfer efficiency
  • Size distribution of bubbles

Fine bubble aeration is an optimal method for enhancing the contact surface between the gas and liquid phases, resulting in a higher mass transfer rate.
In some applications, fine bubble diffusers may be impractical to install or may demonstrate poor efficiency. In these cases, coarse bubble aerators are installed. Moreover, coarse bubble aeration systems are an effective solution for adding turbulence and mixing within the system.

Designing aerated tank reactors is by no means a simple task. THINK Fluid Dynamix® possesses the tools, the team, and the experience to assist our clients in achieving their goals

Aerated stirred tank reactor

Fermentation tanks are critical components in bioprocessing industries, such as pharmaceuticals, food, and biofuels, where they facilitate the controlled growth of microorganisms for the production of valuable metabolites, proteins, or enzymes. Computational Fluid Dynamics (CFD) analysis has emerged as a key tool for understanding and optimizing the performance of fermentation tanks.

CFD analysis provides insights into the hydrodynamics, mixing patterns, and mass transfer processes within fermentation tanks. By simulating the flow around impellers, spargers, and internal structures, engineers can identify areas of poor mixing, uneven nutrient distribution, or excessive shear stress, which can negatively impact cell growth and product yield.

Incorporating bioreactor-specific models, such as oxygen mass transfer, substrate consumption, and cell growth kinetics, into CFD simulations enables a comprehensive understanding of the complex interactions between fluid flow, mass transfer, and biological processes. This allows engineers to optimize operating conditions, such as agitation speed, aeration rate, and nutrient feeding strategy, to achieve desired growth rates and product yields.

Furthermore, CFD analysis can help in the evaluation and optimization of fermentation tank design parameters, such as impeller type, tank geometry, and sparger configuration. By exploring the effects of these parameters on the reactor performance, engineers can make informed decisions that enhance process efficiency and scalability.

CFD simulations can also be combined with experimental data to calibrate and validate models, improving their accuracy and predictive capabilities. This synergy between computational and experimental approaches contributes to the development of more efficient and robust fermentation processes.

In conclusion, CFD analysis has become an indispensable tool for understanding and optimizing fermentation tanks in bioprocessing industries. By providing detailed insights into the complex interplay of hydrodynamics, mass transfer, and biological processes, it enables engineers to make informed decisions that improve overall process efficiency, product yield, and scalability.

In our videos we introduce CFD solutions for aeration and mass transfer

CFD (Computational Fluid Dynamics) analysis of a Rushton Turbine by a time accurate simulation and LES (Large Eddy Simulation) turbulence model.

CFD in the water and wastewater industry: aeration tank

This multiphase simulation uses a Euler-Euler approach to analyse the gas-liquid system. Thanks to this kind of CFD simulation, not only the velocity and the pressure field can be analysed but also the total air hold-up and standard oxygen transfer rate can be calculated.

CFD Transient (time dependent) simulation of the coarse bubble aerator installed in a show and test tank used in the mixing and aeration laboratory.

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