Integrated CFD–PBE Modeling and Experimental Analysis of Glycine Crystallization in Slug Flow Systems

Understanding how hydrodynamics interact with crystallization kinetics in gas–liquid slug flow systems is essential for the rational design of slug flow crystallization (SFC) but remains incomplete. In this work, an integrated computational fluid dynamics population balance equation (CFD–PBE) approach was developed to examine the coupling among local mixing intensity, supersaturation, and crystal growth behavior during glycine crystallization in a slug flow reactor. The CFD simulations describe the velocity, temperature, energy dissipation, and supersaturation fields inside individual liquid slugs, while the PBE captures the kinetics of secondary nucleation and crystal growth based on independently measured parameters. Simulations show pronounced spatial variations in supersaturation and nucleation within each slug, mainly driven by internal circulation and mass transport across the thin liquid film separating the phases. The distributions of Nusselt number and secondary nucleation rate inside the liquid slug were found to be primarily governed by the mixing condition, whereas supersaturation and crystal growth rate closely followed the temperature profile. Experimental data obtained under matching operating conditions were used to validate the model, showing good agreement with predicted crystal size distributions, typically within 20% deviation. The results highlight the key role of slug-scale hydrodynamics in controlling local supersaturation and provide a quantitative framework that links crystal formation mechanisms to reactor-scale flow behavior, offering guidance for the design and scale-up of continuous crystallization processes with controllable crystal quality.