Oscillatory convective structures and solutal jets originated from discrete distributions of droplets in organic alloys with a miscibility gap

The pattern formation process driven by N droplets out of thermodynamic equilibrium, uniformly distributed on the bottom of a container filled with a partially miscible organic liquid, is investigated for different values of N by means of multiprocessor solution of the Navier-Stokes equations. The considered system is intended to model the typical phenomena occurring during the thermal processing of liquid-liquid systems exhibiting a miscibility gap (the so-called "immiscible alloys"). These alloys undergo sedimentation of the separated heavier phase to the bottom of the container under normal gravity conditions. Droplets in non-equilibrium conditions, are responsible for the occurrence of still poorly-known fluid-dynamic instabilities. The present analysis provides a clear and quite exhaustive picture of the different stages of evolution of fluid motion inside the container. The distribution of solute is found to depend on the complex multicellular structure of the convective field and on associated ‘pluming phenomena’. Significant adjustments in the pattern take place as time passes. The structure of the velocity field and the number of rising solutal plumes exhibit sensitivity to the number of droplets and to the possible presence of surface Marangoni effects. New classes of possible instability mechanisms (pulsating, traveling, erratic) are identified and described. The investigation provides "local" details as well as general rules and trends about the macroscopic evolution (i.e. "ensemble behaviors") of the system.