The project ″Modeling Porosity Development during Drying of Liquids and Slurries″ aims to build a mechanistic, three-dimensional model that predicts how internal morphology (e.g., porosity) evolves as gas-saturated slurries dry. Started in September 2023 and updated as of May 2025, the project combines pore-scale simulations and microfluidic experiments to elucidate bubble formation, transport, and interaction in slurries containing dissolved gas in the course of drying.
The model, at its core, captures the dominant physical mechanisms driving drying kinetics: bubble nucleation, growth, coalescence, collapse, gas diffusion, surface evaporation, and capillary effects. These processes were formulated as discrete rules and implemented within a three-dimensional pore-network model. To verify these rules, preliminary two-dimensional microfluidic experiments were performed to monitor bubble dynamics and interface evolution. The observations confirmed key model behaviors, including the transition from concave to convex interfaces and characteristic nucleation and coalescence patterns.
Simulation results showed that the presence of bubbles significantly accelerates drying. Compared to bubble-free systems, bubble networks experienced reduced total drying time, driven primarily by an extended constant rate period. Bubble growth induced internal liquid transport toward the drying surface, maintaining surface wetness and delaying the onset of the falling-rate period.
Spatially, simulations accounting for bubbles exhibited more uniform saturation profiles, whereas in simulations without bubbles pronounced gradients from the surface downward. These findings underscore the role of internal bubble dynamics in redistributing liquid and promoting homogeneous drying. Consistent results across cubic and spherical pore network geometries further demonstrate the robustness and generality of the model.
In the remaining time of the first funding period, the model will be extended to account for solid-particle displacement driven by capillary pressure, enabling full simulation of morphology evolution during drying of a single slurry droplet. Systematic simulations will then be performed across a range of material properties and process conditions. Once this extension is completed, the model will be able to generate the high-resolution datasets required to parameterize a continuum-scale single-droplet model. After model reduction, this continuum model will be integrated into a CFD framework to simulate foaming spray-drying behavior at the tower scale during the second funding period of the project.