Data-driven transport modeling for tracer injection and mixing time screening in stirred tank reactors

Transient CFD of liquid mixing in stirred tanks is too expensive for systematic design studies, and mixing time predictions deviate from experiment even at scale-resolving resolution. Transport-based recurrence CFD (rCFD) decouples scalar transport from the flow solve, replaying a short pre-computed flow database through cell-to-cell displacement maps, so that transport level corrections can be applied without repeating the momentum solution. This is exploited here for the 95% mixing time in a 30 L dual-impeller stirred tank reactor, using a 4.5 s LB-LES flow database from M-Star as the sole input. The rCFD first results inherit the over-prediction of its input flow field (33.1  ±  1.4 s, against 30.1  ±  3.0 s for M-Star and 28.1  ±  2.7 s for Ansys Fluent at comparable spatial resolution, and 25.0  ±  3.0 s measured by conductivity probes in experiment part). Calibrating a single face-swap diffusion parameter in rCFD transport model against one probe measurement brings the prediction to 24.5  ±  1.0 s, recovering experimental agreement without re-running the flow simulation. The rCFD simulation requires approximately 3 s of wall-clock time per second of process time (423 ×  M-Star, 1200 ×  Ansys Fluent) and is almost insensitive to a fivefold increase in extrapolation time step. Ninety injection locations spanning radius, height, and azimuth are therefore screened from the single database in 2.25 h, against estimates of 40 and 113 days for the reference solvers, resolving a 3.6-fold spread in mixing time (13.6–48.8 s) in which injection height and baffle-relative azimuth dominate. The main objective of this work is a fast, spatially and temporally resolved description of scalar transport; the 95% mixing time is used as the quantitative metric for validating it against sparse experimental data.

Content

DDC Class

660.284: Chemical Reactors

530.42: Fluid Physics

Funding References

Funding(s)

SFB 1615 - SMARTe Reaktoren für die Verfahrenstechnik der Zukunft

SFB 1615 - Teilprojekt B05: Von Sensoren und Trajektorien zu Transport und Mischung

SFB 1615 - Teilprojekt C04: SMARTe kontinuierlich betriebene Wirbelschicht zur Sprühgranulation mit selbstregulierender Verweilzeitverteilung