Enhancing Mixing Process Using Computational Fluid Dynamics

The mixing of two or more fluids is a process most commonly found in many industries, having a substantial importance in almost every production process as well as industrial and consumer products. Examples include mixing of dye into liquid, or food ingredients mixed together in food processing or mixing of gases diffusing into one another. The number of opportunities for mixing technology is unlimited, which is a reason why this technology is considered as a large area for research.

Some of the common applications of fluid mixing can be found in chemical, pharmaceutical, water-treatment, paper, bio-reactor and food industries. Of all these applications, studying the mixing behavior remains a prime factor to evaluate the mixing technology employed. Some common assessment questions from a mixing process shall include how these fluids will interact and how long will they take to reach a state of uniformity.

Mixing process is usually undertaken using mixing or agitating tanks utilizing impeller and baffles. However, the process may vary depending on how the substances are being mixed. The table below shows some of the common mixing processes according to physical and chemical applications.

Physical Processing

Application Class

Chemical Processing

Suspension

Liquid-Solid

Dissolving

Dispersion

Liquid-Gas

Absorption

Emulsification

Immiscible Liquids

Extraction

Blending

Miscible Liquids

Reactions

Pumping

Fluid Motion

Heat Transfer

The impellers on the other hand are usually axial or radial and are characterized by the direction of the fluid motion generated by blades. The mixing efficiency of the tank is also based on baffle configurations. A tank without baffles will produce no vertical currents and affect the mixing process. As such, locating and sizing the baffles is an important aspect to enhance the mixing process.

Annually, industries spend huge amount in improving the processes and technologies that helps in better mixing of fluids in order to avoid loosing millions due to non-efficient mixing, affecting product quality. As such, process engineers rely on computational fluid dynamics (CFD) in order to evaluate the mixing tanks more comprehensively. CFD simulations allow engineers to determine when and how enhanced mixing can be achieved. Additionally, these tools indirectly assist in improving the product development process and quality, reducing the waste and operational cost to a significant level.

The simulation process requires developing the tank geometry and defining the fluid properties with suitable turbulence models to capture the physics accurately. In case of a multiphase fluid mixing scenario, CFD helps in determining the process of dissolution or reaction more effectively, allowing engineers to optimize the feed uniformity.

A solid-liquid mixing simulation will also help in determining particle distribution and identify regions across the tank that is prone to erosion. Moreover, CFD studies assists in determining transient events such as the required mixing time for two fluids to achieve uniformity.

About Author:

Mehul Patel specializes in handling CFD projects for Automobile, Aerospace, Oil and Gas and building HVAC sectors. He works as a CFD consultant with Hi-Tech CFD for the past 5 years and has successfully executed numerous CFD projects of high complexities. He is an expert in turbo-machinery, gas dynamics, Combustion, Fluid Dynamics, multiphase flow analysis, computational fluid dynamics etc.

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