Mixing and homogenization


In industrial process engineering, mixing is a crucial unit operation that involves manipulating a heterogeneous physical system to create a more homogeneous mixture. Homogenization refers to the minimization of concentration gradients of various compounds or temperature gradients within the entire system. This unit operation is vital for the treatment of wastewater and drinking water and for numerous chemical processes, ranging from food products in grocery stores, healthcare and pharmaceutical products, to polymers, minerals, paint and coatings, biofuels, and more.

To minimize investment and operating costs while maximizing the performance of stirred reactors, Computational Fluid Dynamics (CFD) provides a proven tool for designing optimal mixing solutions. The traditional approach of costly and time-consuming experimental trial and error is no longer necessary. Today, it is feasible to reliably simulate numerous designs in a short time, saving time, capital expenditure, and operating costs.

High-performance CFD enables the simulation of various problems and tasks in operations and the analysis and evaluation of critical process parameters, including:

  • Suspension of solid matter and analysis of the specific mixing power needed to achieve a defined height of suspension.
  • Blend time analysis for any reactor and mixing system.
  • Flow distribution analysis in multiple tanks.
  • Mixing patterns, flow velocities, and turbulent dissipation analysis for various types of liquids (Newtonian and non-Newtonian) across all Reynolds number ranges.
  • Retention Time Distribution (RTD) analysis for Complete Stirred Tank Reactors (CSTR) in a series.
  • Heat distribution and heat transfer analysis, among others.

Industrial and water engineers have always been motivated by the pursuit of achieving the highest mixing efficiency. THINK Fluid Dynamix® possesses the tools, personnel, and experience to assist our clients in reaching their objectives.

Activated sludge tanks

Activated sludge tanks are essential components of wastewater treatment plants, where microorganisms metabolize organic matter and transform it into a stable end product. A well-designed tank facilitates effective mixing, aeration, and settling, ensuring optimal conditions for biological degradation.

CFD simulation allows engineers to gain insights into the complex hydrodynamics, mixing patterns, and aeration efficiency within the activated sludge tanks. It provides a virtual environment to evaluate and optimize various design parameters, such as tank geometry, inlet and outlet locations, and the placement of aeration devices. This enables the identification of dead zones, short-circuiting, and uneven distribution of oxygen and nutrients, which may hinder the treatment process

Flocculation tanks

Flocculation tanks serve to aggregate small suspended particles into larger flocs, making it easier for subsequent sedimentation or filtration stages to remove them from the water.

CFD analysis provides valuable insights into the hydrodynamics, mixing patterns, and residence time distribution within flocculation tanks. By simulating the flow patterns, engineers can identify areas of poor mixing or short-circuiting, which may result in inefficient floc formation or floc breakup. CFD models also allow for the optimization of key design parameters, such as tank geometry, baffle configuration, and impeller type, to achieve desired performance objectives.

Moving Bed Biofilm Reactor (MBBR)

Moving Bed Biofilm Reactors (MBBR) are an innovative wastewater treatment technology that combines the advantages of both suspended and attached growth systems. In MBBR, microorganisms grow on the surface of carrier media that freely move within the reactor, providing a larger surface area for biofilm development and improved treatment efficiency. Computational Fluid Dynamics (CFD) simulations have become essential for understanding and optimizing MBBR performance.

In order to accurately simulate the carrier media movement within the MBBR, a Lagrangian multiphase approach is employed. This approach models the carrier particles as discrete entities, allowing for a two-way coupling interaction with the flow. The particles‘ motion is influenced by the flow, while their presence also affects the flow dynamics. By incorporating collision kinetics, the Lagrangian multiphase approach can represent the MBBR media’s behavior as realistically as possible.

Parameters such as density and drag coefficient of the carrier particles are critical for accurately predicting the motion and interaction within the MBBR system. These parameters can be calibrated using experimental results, enhancing the fidelity of the CFD model and its ability to replicate the actual reactor performance.

The CFD simulation, with its refined multiphase approach, can provide valuable insights into the hydrodynamics, biofilm growth, mass transfer, and pollutant removal within the MBBR. By examining the flow patterns and media interactions, engineers can optimize reactor design and operating conditions to ensure maximum treatment efficiency

Blend time in stirred tank reactor

Stirred tank reactors are widely used in various industries, including chemical, pharmaceutical, and bioprocessing, for carrying out mixing, reaction, and mass transfer operations. One critical parameter in the design and operation of stirred tank reactors is the blend time, which refers to the time required to achieve a specified degree of homogeneity within the reactor. Computational Fluid Dynamics (CFD) simulations have emerged as a valuable tool for predicting blend time and optimizing the performance of stirred tank reactors.

CFD simulations can provide detailed insights into the flow patterns, mixing dynamics, and velocity fields within the reactor, making it possible to accurately estimate the blend time. By simulating the flow around impellers, baffles, and other internal structures, engineers can identify areas of poor mixing or stagnant zones, which may contribute to longer blend times and reduced process efficiency.

In addition to analyzing the hydrodynamics within the reactor, CFD simulations can also incorporate mass transfer models, which help in predicting the mixing of different species and the consequent blend time. These models account for the diffusion and convection of solutes and can be coupled with reaction kinetics to simulate complex processes occurring within the stirred tank reactor.

Using CFD simulations, engineers can explore the effects of various design and operating parameters on blend time, such as impeller type, rotational speed, tank geometry, and baffle configuration. This enables them to make informed decisions on optimizing reactor design and operating conditions to achieve the desired blend time and overall process efficiency.

Industrial mixing

Industrial mixing is a critical operation in numerous industries, including chemical, pharmaceutical, food, and cosmetics, where homogenization, blending, and dispersion of various components are essential for achieving desired product quality. Computational Fluid Dynamics (CFD) simulations have emerged as a vital tool for understanding and optimizing mixing processes in industrial settings.

CFD simulations provide valuable insights into the complex flow patterns, velocity profiles, and turbulence characteristics within mixing vessels, enabling engineers to identify areas of poor mixing or stagnation zones. By simulating the flow around impellers, baffles, and other internal structures, CFD models help predict the mixing efficiency, blend time, and power consumption for different design and operating conditions.

Incorporating mass transfer and chemical reaction models into CFD simulations allows for a comprehensive understanding of the complex interactions between fluid flow, species distribution, and reaction kinetics. This enables engineers to optimize the mixing conditions for specific processes, such as solids suspension, gas-liquid dispersion, or emulsification, ensuring that the desired product quality is achieved.
By exploring the effects of various design parameters, such as impeller type, rotational speed, vessel geometry, and baffle configuration, engineers can make informed decisions on the optimal mixing equipment and operating conditions. This leads to improved process efficiency, reduced energy consumption, and minimized production costs.

Moreover, CFD simulations can be combined with experimental data to calibrate and validate models, enhancing their accuracy and predictive capabilities. This synergy between computational and experimental approaches helps engineers refine the design of mixing systems, reducing the need for costly trial-and-error processes.

Unsteady simulation of the blending of two liquids in a stirred tank by means of a Rushton Turbine.

The INVENT HYPERCLASSIC® Mixer shows remarkable features such as the uniformity of the flow generation, the energy input at the bottom and the creation of a „Virtual Wall“ between two mixers rotating in opposite directions.

This multiphase transient CFD Simulation shows the velocity field and the concentration of solids in a stirred tank reactor.

Transient CFD Simulation of the mixing time of a propeller in a reactor.

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