Molecular dynamics calculations of the enthalpy of vaporization for different water models

Abstract

Phase-change heat transfer processes involving water play a key role in numerous societal applications, such as electrical power generation, microelectronics cooling, or water desalination. Advanced computational tools, such as molecular dynamics (MD), are increasingly being used to simulate these processes, especially on nanostructured surfaces and in nanoparticle suspensions, to gain insight into the unique nanoscale physics at play. In these studies, it is critical to use models of the water molecule that yield accurate predictions of water’s thermophysical properties, particularly its enthalpy of vaporization. Here, we use MD to determine the enthalpy of vaporization (hfg) for six common water models and four different values of the cutoff radius (i.e., the intermolecular distance beyond which interactions are simplified or ignored). The most accurate prediction of hfg (within 2 % of the value tabulated by ASHRAE) comes from the TIP3P water model with a cutoff radius of 14 Å. We also conducted a preliminary study of the variation of hfg with pressure and found reasonable agreement between simulations and tabulated ASHRAE data (<7% error). This work provides physical insights into the sensitivity of the predicted macroscopic thermophysical properties of water to minute changes in the atomic-level properties and is expected to inform future MD-based studies of phase change processes of water, especially as they occur at elevated pressures and on nanostructured surfaces and in nanoconfined geometries.