Modelling of blending of Newtonian fluids using bespoke static mixer geometry

EPSRC: Thomas Robinson: EP/S023070/1



Static mixers are solid structures that can be inserted into process piping to homogenise a fluid flow as it passes through it. This means that at any point in the pipe, the fluid is the same as at any other point. Currently, multiple different designs of static mixer exist, and the two most eminent static mixers are the Chemineer KM mixer and the Sulzer SMX mixer. These came to prominence in the early 1980s and most sold static mixers are derivative of these two designs. As part of my Chemical Engineering Master's thesis at the University of Birmingham, I worked with CALGAVIN LTD on the design of a brand-new static mixer design and compared it against those current market leaders. To assess the capabilities of this design we employed the use of Planar Laser-Induced Fluorescence (PLIF).
Put simply, if a mixture of two separate fluids is pumped into the inlet of static mixer, at the outlet of the mixer, the two fluids will have become more mixed. If you add a dye that fluoresces under laser light to one of the initial fluids, you can shine a laser at the outlet of the static mixer to make the dye give off light. This light can be captured with a camera and generates an image that shows the distribution of the fluid in the pipe after mixing. By doing some post-processing and calibration, the exact concentration of each fluid can be calculated from this image as well as a value for how mixed it is. Different static mixers and different flow conditions (temperatures, viscosities, velocity, etc...) can be tested and compared to find which static mixer offers the best mixing. The PLIF research validated the new static mixer and showed it has promise against the KM-type and SMX-type mixers.
This PLIF technique can be used to rapidly iterate a new static mixer design but it has inherent downsides. Like when mixing squash and water, they cannot be unmixed. It is the same with the PLIF experiments, the test fluids are irreversibly mixed. When this test fluid is expensive, it adds significant costs to experimental testing. To mitigate this expense, this 12-week research project has been proposed.
The premise is to use Computational Fluid Dynamics (CFD) to run analogous testing in computer simulations. If the simulations can be accurately mapped to the experimental results that have already been taken, it will allow a computer to test multiple small design changes to the static mixer that could never all be tested experimentally. This proposal represents a significant benefit to both the UK and Canadian parties involved. The University of Birmingham and CALGAVIN will gain access to the expertise of the modelling team in the University of Alberta and in return, they will receive world-class experimental data that can be used to hone their simulations to match real work experimentation.
The output of this research will, therefore, be higher confidence in more accurate CFD simulation techniques as well as drastically lower development costs of the new static mixer with increased chances of it becoming a viable market product.