Insight to the Liquid Vapor Phase Change Processes Using Molecular Dynamics Method.

PhD Theses.In this thesis, condensation process has been first addressed. The dependences of formation and transition of condensation mode on surface wettability ( ) and temperature difference T ) is explored . F ive formation mechanisms and two transition mechanisms are revealed. Meanwhile, the dependence of nano confined surface condensation on tangentially external force field ( f e ) is considered. The dynamic behaviours of nano confined surface condensation are analysed. The heat transfer analysis shows that f e indirectly influences the interfacial thermal resistance by direct influence on condensation. Results also show that as f e increases or decreases, the dissipated heats increase and gradually take over the total transferred heat, which finally reduces or suppresses the occurrence of condensation. Furthermore, the growth and self jumping of single droplet on the nanostructured surfaces are systematically investigated. The MD simulation has proved the effectiveness of self jumping of single nanodroplet driven by Laplace pressure. The results show tha t increasing the surface wettability and size of the pinning site promotes the droplet growth but blocks the droplet self jumping. Secondly, this thesis has focused on the liquid to vapor process . How to maintain and enhance nanofilm evaporation on nanopi llar surfaces are systematically investigated. The results show that the smaller pitch between nanopillars and larger diameter of nanopillars can enhance evaporation but also raise the possibility of boiling, whereas the smaller height of nanopillars can e nhance evaporation and suppress boiling. T he nanofilm thickness should be maintained beyond a threshold to avoid the suppression effect of disjoining pressure on evaporation. Additionally, the generation and evolution of nanobubbles on nanoparticles ( are studied. The results demonstrates that the superhydrophobic GNP is favourable Abstract V for fast and energy for fast and energy--saving nanobubble generation. saving nanobubble generation. Increasing Increasing heating intensity (Q) can can promote the generation and growth of nanobubbles for a given promote the generation and growth of nanobubbles for a given . . The maximum radius of The maximum radius of the nanobubble is found to be dependent on the nanobubble is found to be dependent on and not Q