Spreading, Solidification And Remelting Behavior Of Liquid Metal Droplets Sequentially Impinging Onto A Metal Substrate

Abstract

The fluid dynamics and simultaneous solidification of two successive molten metal droplets impacting a flat substrate is investigated numerically. The primary objective is to investigate the effects of initial droplet and substrate temperature, and the latent heat of substrate material, on the spreading, solidification and remelting of molten tin droplets impacting a substrate of the same material. A robust fluid-flow solver that is capable of modeling rapidly deforming free surfaces involving a moving phase-change boundary is employed in the study. The Navier-Stokes equations are solved using a finite volume formulation. A two-step projection method is used to solve for incompressible flow. The free surfaces of the droplets are tracked by the volume-of-fluid method with a second order accurate piecewise linear scheme. The surface tension force is modeled by the continuum surface flow model. The energy equation is modeled using an enthalpy-based formulation. The predictive model used in this study enables the optimization of operating parameters to reveal impinging droplet temperatures and initial substrate temperatures that promote substrate remelting, possess good flow characteristics and yet, minimize thermally induced stresses and excessive remelting of previously deposited material. The results of this investigation are relevant to droplet deposition technologies involving large diameter droplets at low velocities.