Predict Flow Field and Mixing Time for High-Shear Mixers Using CFD

Batch high-shear mixers are used in a variety of different processing industries,such as the pharmaceutical, chemical and food industries. One company that utilize this type of mixers is Tetra Pak. High-shear mixers can be used for many different mixing scenarios, but only liquid-liquid mixing is discussed in the thesis. The batch high-shear mixer is constructed with a rotor-stator at the bottom of the tank. The rotor stator structure is a rotor which rotates inside the stationary stator. The fluid effected by the rotor is pushed through small holes on the stator and out into the tank region. The flow field generated inside the vessel is both complex and highly turbulent. With the technology of today it is highly interesting to use Computational Fluid Dynamics, CFD, simulations to determine these performances, from both an economically and time-dependant perspective. One property that is interesting is the time the mixing tank needs to achievea homogene mixture, i.e. the mixing time. However, simulations regarding rotor-stator mixers are in general very computational demanding. It is therefore of interest to improve the methodology to decrease the simulation time while still giving realistic results. This thesis evaluates Tetra Paks current methodology and also suggests possible improvements. The methodology can be divided into two parts, predicting the flow field inside the tank and predicting the mixing time.To decrease the simulation time, Tetra Pak uses a time-scale separationmethod in the current methodology. The separation utilizes that the flow around the rotor-stator converges to a stable state quicker than the rest of the vessel.The stabilized flow is then approximated by boundary conditions. Different boundary conditions have been tested. Of all methods, a transient boundary condition which imitates the motions of the rotor-stator was deemed generate the most realistic flow field. The second best option was a time-averaged boundary condition, simulated wit
Food processing is a cornerstone of today's society. Almost all products on the store shelves are created from some sort of processing line. In these lines, high-shear mixers are often used for combining the different ingredients. To understand how this machinery works and make the process more efficient, the flow field inside the mixer is analyzed. Preferably, Computational Fluid Dynamics (CFD) is used to simulate the flow instead of costly physical experiments. However, due to the complex geometry of this mixer these simulations are very time-consuming. The goal of this thesis is therefore to create a CFD-methodology which is both time effective and yields realistic results.