Molecular dynamics simulation of evaporation and explosive boiling over nanostructured surfaces
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[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] Evaporation and boiling is important for many processes including removal of CO2 from the anode of methanol fuel cells, electronic cooling and various microfluidic applications. Phase change over nanostructured surface is difficult to understand and control for several reasons, including the complexity of geometry, complicated formation of bubble generation between nanostructures, the multiple time and length scales involved. This thesis was concerned with evaporation and boiling over nanostructured surface on nanosecond time scales. The focus was on the effects of nanostructures shape and material. The main tool for these studies was non-equilibrium molecular dynamics simulation under NVT and NVE ensembels. The thesis consist of two main parts: a) A Molecular Dynamics (MD) simulation is carried out to investigate the normal and explosive boiling of thin film adsorbed on a metal substrate whose surface is structured by an array of nanoscale spherical particles. The molecular system was comprised of the liquid and vapor argon as well as a copper wall. The nanostructures have spherical shape with uniform diameters while the thickness of liquid film is constant; hence the effects of transvers and longitudinal distances as well as the diameter of nanoparticles are analyzed. The simulation was started from an initial configuration for three phases (liquid argon, vapor argon and solid wall); after equilibrating the system at 90 K, the wall is heated suddenly to a higher temperature that is well beyond the critical temperature of Argon. Two different superheat degrees was selected: a moderately high temperature of 170 K for normal evaporation and much higher temperature 290 K for explosive boiling. By monitoring the space and time dependence of temperature and density as well as net evaporation rate, we obtained the detailed microscopic pictures of the normal and explosive boiling process on a flat surface with and without nanostructures. The results show that the nanostructure has significant effect on evaporation /bo
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