Molecular dynamics study of nanoscale boiling characteristics: Effects of wall temperature and system pressure

Most molecular dynamics (MD) boiling studies focus on atmospheric or low pressures, leaving the wetting and boiling behavior of water on zirconium at reactor-relevant pressures insufficiently understood. The solid–liquid interaction strength was first varied, and the parameter for subsequent simulations was selected by comparison with the experimental contact-angle range of zirconium alloys. Wettability was examined at 15.5 MPa and 300–538.15 K, followed by boiling simulations at wall temperatures of 650–950 K and pressures of 0.1–15.5 MPa. The contact angle decreased with temperature, more sharply at higher temperatures. Increasing wall temperature advanced nucleation, whereas increasing pressure delayed it. An empirical correlation relating incipient nucleation time to wall temperature and pressure reproduced the simulation results within ±15%. Before nucleation, the near-wall water layer heated faster than the bulk. Higher wall temperature increased the near-wall-to-bulk temperature difference and the initial heat flux, whereas pressure had comparatively little direct effect on near-wall heating, heat flux, or effective interfacial thermal resistance and mainly prolonged sensible-heat accumulation by delaying nucleation. After nucleation, heat-transfer deterioration resulted from reduced effective solid–liquid contact: higher wall temperature accelerated vaporization, whereas higher pressure helped maintain the near-wall liquid film. Energy analysis indicated that increasing wall temperature enhanced the energy-supply rate, while increasing pressure slowed the growth of the near-wall average potential energy, thereby extending the time required to reach nucleation conditions. These findings provide molecular-scale insight into nanoscale boiling under high-superheat conditions on zirconium surfaces at reactor-relevant pressures.