The structural randomness of porous media presents significant challenges to accurately simulating colloidal transport. The Boltzmann transport equation (BTE) provides a reliable way to simulate the microscopic dynamics of colloidal particles in random space.
By using the Chapman-Enskog (CE) method, a macroscopic advection-diffusion transport model is derived from the BTE. It includes a diffusion term depending on the particle velocity distribution, a velocity delay term, and a capture term reflecting the microscopic capture mechanism, which tends to preferentially capture high-speed moving particles. These terms account for the delay and capture effects in colloidal transport. Meanwhile, the explicit expressions of the three transport coefficients are presented to provide a quantitative basis for the application of the model.
The model is effective at small mixing filtration coefficients λl. By comparing outlet concentration profiles of different models (Fig. 14), we clarify the impact of this mechanism on the advective velocity delay and capture efficiency. The model resolves some of the paradoxes of traditional colloidal transport models. And it agrees with previous models under specific conditions.