Micro-scale fluid model for drying of highly porous particle aggregates

A discrete three-dimensional model for the fluid flow and phase transition at the microscopic scale during convective drying of highly porous particle aggregates has been developed. The phase distributions are described by time-dependent cell volume fractions on a stationary cubic mesh. The solid phase volume fractions are computed from an arbitrary collection of spherical primary particles generated by gravitational deposition using the discrete element method. The volume of fluid method is used to track the liquid–gas interface over time. Local evaporation rates are computed from a finite difference solution of a vapor diffusion problem in the gas phase, and the liquid–gas interface dynamics is described by volume-conserving mean curvature flow, with an additional equilibrium contact angle condition along the three-phase contact lines. The evolution of the liquid distribution over time for different wetting properties of the solid surface as well as binary liquid bridges between solid particles are presented.

► First steps toward explaining macroscopic behavior from micro-scale phenomena. ► Quasistatic approach by assuming scale separation in time (slow evaporation). ► Local evaporation rates from solution of vapor diffusion problem in the gas phase. ► Liquid–gas interface dynamics described by volume-conserving mean curvature flow. ► Illustration: evolution of liquid distribution for different solid wetting properties.