Sulzer streamlines CFD
3 Jul 2006
While standard CFD solvers can calculate velocity and pressure fields it is much more challenging to simulate the laminar flow concentration distributions necessary for predicting homogeneity in static mixing.
CFD simulation is generally used in the optimisation and design of many mixing processes for describing the momentum exchange between the different phases and various complex flow processes.
While standard CFD solvers can calculate velocity and pressure fields it is much more challenging to simulate the laminar flow concentration distributions necessary for predicting homogeneity in static mixing.
With laminar flow, fluid moves along parallel streamlines without transverse movement, with molecular diffusion being the main mechanism for equalising concentration. Bars and walls are used in static mixers to achieve mixing by repeated division and recombination of liquid flowing around these elements.
Standard CFD schemes for predicting the concentration distributions within mixers intrinsically overestimate the mixing efficiency, as they suppress the effects of natural molecular diffusion, explains Sebastian Hirschberg, senior engineer, fluid technology, at Sulzer Innotec.
To tackle this issue, Sulzer Innotec developed a model that approximated the effect of the Brownian motions involved in diffusion by varying the end-points of the stream lines. This, said Hirschberg, has yielded a diffusion coefficient for the laminar flow mixing that allows accurate evaluation of concentration distributions.
From this work, Sulzer Innotec has developed a CFD code, which is now in use at sister company Sulzer Chemtech for accurate simulation of laminar mixing processes. The company, added Hirschberg, has gained an understanding of static mixing processes that would not have been possible with other methods.
