Numerical simulation on evaporation characteristics of nanofluid droplets

This study establishes a multiphysics numerical model to investigate the evaporation dynamics of nanofluid droplets on heated substrates by employing the Arbitrary Lagrangian-Eulerian (ALE) method. The model fully couples internal and external fluid flow, heat transfer, and mass transport, while tracking nanoparticle motion within the droplet through a particle-tracing approach. Particular attention is given to the evolution of temperature fields, vapor concentration distributions, interfacial mass fluxes, and the trajectories of suspended nanoparticles during different evaporation stages. The results show that substrate heating and surface evaporative cooling jointly establish a surface tension gradient that drives Marangoni circulation within the droplet. As the droplet gradually flattens, the internal flow evolves from a single vortex into a multiple-vortex structure, with four vortices forming at 70 s during late-stage evaporation. This multiple-vortex structure persists for approximately 12 s, causing local perturbations in interfacial temperature and evaporation flux. The evaporative mass flux at the liquid-gas interface is higher near the droplet edge than at the center. During early evaporation, the mass flux near the edge reaches approximately 0.03 kg/(m²·s). As evaporation proceeds, the convective mass flux gradually decreases, whereas the diffusive mass flux remains relatively stable at approximately 0.005 kg/(m²·s). Nanoparticles migrate and accumulate under the influence of the internal flow, becoming trapped at the liquid-gas interface or deposited on the substrate. These findings reveal the coupling among temperature, flow, and mass transport, as well as nanoparticle migration patterns during nanofluid droplet evaporation. They provide a theoretical reference for the application of nanofluid working fluids in loop heat pipes for space applications.