A Lattice Boltzmann Simulation of Contact Line Motion and Internal Fluid Flows in an Evaporating Droplet on Homogenous Substrates

概要

論文の詳細を見る
A two-dimensional lattice Boltzmann model is performed to simulate the evaporation of a single droplet on a homogeneous wetting substrate. An evaporation model is applied to the present simulation to describe the mass loss from the surface of an evaporating droplet. In addition, a partial wetting boundary condition is forced to the lattice site of a substrate surface to give the wettability of the substrate. Evaporation of a single droplet in ambient vapor illustrates a linear decrease in the droplet radius square, which agrees well with the d-square law for an evaporating droplet. In the evaporation of a droplet on a hydrophobic substrate, the wetting diameter decreases while the contact angle remains constant during the evaporation process. In the evaporation of a droplet on hydrophilic substrate, the wetting diameter decreases while the contact angle remains almost constant when a partial wetting boundary condition is forced. However, three stages of contact line motion are observed when the partial wetting boundary condition is modified to describe the dynamical change of the contact angle, which agrees well with the experiment of water droplet evaporation by Shanahan and Bourgès (1944). In addition, internal fluid flows towards the contact line of the droplet are discussed in the pinning stage of the evaporation.