Mechanism study on spreading dynamics of nanofluids droplet coupled with thermal evaporation

Abstract

Droplet-wall interactions occur in many advanced engineering technologies, such as 3D printing, spray coating, and even quantum light-emitting diode(QLED). Nanofluids (colloids of nanoparticles) are becoming increasingly important working fluids for more excellent performances. Computer modeling of fluid flows with the large deformation of free surface usually presents great challenges for conventional grid-based numerical methods. The smoothed particle hydrodynamics (SPH) method has been widely used in such droplet dynamics because of its meshless Lagrange methods, as well as the applicability to macro-scale simulation. In the paper, the numerical model based on the SPH method is presented to predict the detailed outcome of sessile and transient nanofluid droplets. The surface tension of droplets is taken into consideration by the inter-particle interaction force (IIF) model for its advantages in modeling the contact angle during wetting. The properties of nanofluids are obtained by averaging the properties of base fluids and nanoparticles, based on the assumption that nanofluids of low concentration are a homogeneous mixture and Newtonian fluid. The assumption is proposed based on the rheological measurement of nanofluids. Heat conduction is added into the SPH model when the impacted surfaces are heated, and the evaporation is modeled by “extinguishing” the SPH particles. The SPH model predicts the evolution of the droplet surface from spreading to receding, even rebounding on the wall. Moreover, the normalized droplet diameters predicted by the SPH model agree well with the experimental data from the high-speed camera. The proposed SPH models have been used to study the effects of heating temperatures and nanofluids concentration on droplet-wall interactions. The modified SPH models can handle the nanofluids droplet dynamics, along with large deformation, thermal transfer, and evaporation. The results demonstrate that the SPH model is a powerful tool to study the complex droplet dynamics and to predict the patterns of droplet deformation as well as the thermal distribution.