2D LATTICE BOLTZMANN SIMULATION OF A MICRO MOLTEN DROPLET’S DYNAMICS AND SOLIDIFICATION ON A COLD SURFACE
In this paper, a newly developed multi-component/multi-phase (MCMP) phase-change lattice Boltzmann model (LBM) is applied to study the dynamics and heat transfer of an impinging molten solder (Sn-Pb alloy) droplet on a horizontal cold surface. Effects of surface wettability and wall temperature on droplet dynamics and solidification are investigated numerically. It is found that after impacting with a cold surface, the droplet undergoes an oscillatory motion on a wetting surface while it undergoes a bouncing motion on a non-wetting surface. The former motion is owing to the generation of vortex inside the droplet. Solidification inside the impinging molten droplet begins as soon as heat is transferred from the cold surface. The solidification effect is weak in its initial spreading period, and the solidified portion grows larger in the subsequent recoiling period. The local solidification at the contact line formed during recoiling motion can hamper the bouncing behavior on a non-wetting surface. The droplet keeps on oscillating and cooled by the cold surface until it completely solidifies into a bump. Finally, a map in terms of Stefan (Ste) number versus contact angle is obtained for predicting droplet oscillation or bouncing motion, providing a guide for selection of parameters to avoid occurrence of bouncing behavior of the droplet.