Molecular dynamic simulation of platinum heater and associated nano-scale liquid argon film evaporation and colloidal adsorption characteristics

A novel 'fluid-wall thermal equilibrium model' for the wall-fluid heat transfer boundary condition has been developed in this paper to capture the nano-scale physics of transient phase transition of a thin liquid argon film on a heated platinum surface and the eventual colloidal adsorption phenomenon as the evaporation is diminishing using molecular dynamics. The objective of this work is to provide microscopic characterizations of the dynamic thermal energy transport mechanisms during the liquid film evaporation and also the resulting non-evaporable colloidal adsorbed liquid layer at the end of the evaporation process. A nanochannel is constructed of platinum (Pt) wall atoms with argon as the working fluid. The proposed model is validated by heating liquid argon between two Pt walls and comparing the thermal conductivity and change in internal energy to thermodynamic properties of argon. Later on, phase change process is studied by simulating evaporation of a thin liquid argon film on a Pt wall using the proposed model. Gradual evaporation of the liquid film occurs although the film does not vaporize completely. An ultra-thin layer of liquid argon is noticed to have "adsorbed" on the platinum surface. An analysis similar to the theoretical study by Hamaker (1937) is performed for the non-evaporating film and the value of the Hamaker-type constant falls in the typical range. This analysis is done to quantify the non-evaporating film with an attempt to use molecular dynamics simulation results in continuum mechanics. (C) 2008 Elsevier Inc. All rights reserved.