Mesoscale Modelling of Multiphase Flow and Wetting

My project aimed at building a computational model to study ink penetration in paper, which is relevant to the ink-jet printing industry. Jetting ink is a complex formulation composed of a solvent like water, co-solvent such as glycerol, surfactants, dye molecules, nanoparticles and polymers. On the other hand, print paper is equally complex due to the disordered arrangement of the cellulosic fibres giving rise to complex pore shapes and a wide distribution of their sizes. Tackling these complexities at once deem the problem intractable. Thus, we started with the simplest model of a solid and fluid, and elevated complexities of the respective materials.

A mesoscale computational technique called Many-body Dissipative Particle Dynamics (MDPD) is chosen based on the length and time scales pertinent to imbibition in porous paper. Simulations are first bench marked against Lucas-Washburn theory describing pure fluid imbibition (simple fluid) into a cylindrical nanopore (simple solid). A second fluid component is added to the pure fluid to study binary mixture imbibition in a nanopore. Next, we investigate pure fluid flow through a complex solid achieved by positioning rigid micro pillars in irregular patterns. Simulation results agree excellently with experiments, thus proving the capability of MDPD to handle complex flow geometries. Finally, imbibition simulations of a dye like liquid into a stack of disordered fibres generate deposition patterns and penetration rates that qualitatively resemble experimental observations.