Imperial College experts claim fluid mixing breakthrough

London - Fluid mechanics experts at Imperial College London have developed a fluid mixing technology that, they claim offers significant economic benefits over current industrial mixers in the process industries. The technology is based on "Fractal Flow Control (FFC) Grids" - fractal-patterned meshes, which can be applied to any fluid flow for the controlled mixing of fluids.

According to ICL, FFC Grids are an alternative to current static in-line mixers for fluid mixing and can also be used for mixing a fluid and a gas to create homogenous end products. Target applications include the chemical and petrochemical industries for additive mixing, dilution of reagents, chlorination or oxidation; in waste and water treatment for aeration, sludge mixing and chemical addition as well as for generating powders in the pharmaceuticals industry.

Professor Christos Vassilicos from Imperial’s department of aeronautics pioneered the development following years of research into turbulence in mixing and flow control. His team carried out wind tunnel experiments to examine the turbulence generated by fractal grid structures, which showed that they could be used to subtly control and manage the transition from laminar to turbulent flow.

The research team also carried out tests in a water flume to investigate the scaling and decay of turbulence generated downstream of different two-dimensional fractal grids. These tests showed that slight alterations in the grid's dimensions - fractal parameters such as bar thickness and fractal dimension - related directly to the turbulence intensity generated by the fluid’s impact with the grid, as well as on the pressure drop across it.

Moreover, the tests showed that it was possible to independently set the levels of turbulence intensity and pressure drop and that the fractal grids could be designed to generate high turbulence intensities with low pressure drops - creating optimised energy-efficient mixers.

The research team went on to compare the mixing and drag performances of Imperial’s Fractal Flow Control (FFC) Grids with those of a commercially available top-performance industrial mixer. The findings suggested that the FFC Grids technology had several advantages in terms of improving mixer performance (see panel below) with many more potential opportunities for effective mixing engineering and design still to be explored.

According to Vassilicos, the most impressive results were obtained when a Fractal Flow Control Grid and current technology were combined in the pipeline. This combination, he said, “offers the very tangible possibility of setting an entirely new standard of high quality mixing with homogeneous concentration maps and profiles, as well as little action on the walls, and at a very short distance downstream from the mixing elements.”