Dissipative particle dynamics model for colloid transport in porous media

We use a dissipative particle dynamics (DPD) model to study colloid transport in porous media. Unlike many existing numerical models, the DPD model directly couples dynamics of the fluid and colloidal particles. In the model, fluid, colloids, and soil grains are all represented by DPD particles. The interaction between particles is modeled by central and non-central DPD forces, which conserve both linear and angular momentums exactly. Additional van der Waals forces are applied between colloids and collectors. Other transport processes, including gravitational sedimentation, interception of colloids by soil grains (acting as colloid collectors) due to a finite size of colloids, and the Brownian diffusion of colloids are also included in the DPD model. We use the DPD model to study the contact efficiency in colloid filtration in saturated porous media and compare our results with empirical models based on filtration theory. Results of the DPD model agree well with the empirical models for low-concentration suspensions and colloids being small relative to the collector size. For colloid suspensions with larger colloids (relative to the collector size) and/or higher concentration, the agreement between the DPD model and the empirical models deteriorates. In the transport of a concentrated suspension of large colloids, the fluid flow is strongly affected by the linear and angular motions of the colloids, which are mainly disregarded in filtration theory. On the other hand, the DPD model fully couples the fluid flow and colloid transport and, thus, is expected to be accurate for a wide range of colloid sizes and concentrations