Critical Threshold for Bubble-like Nucleation during Pseudoboiling at Supercritical Pressures

Area of Science:

• Thermodynamics and Fluid Mechanics
• Materials Science and Nanotechnology

Background:

• Supercritical pseudoboiling, observed macroscopically, involves evaporation-like and boiling-like heat transfer.
• Previous studies have experimentally quantified its contribution to heat transfer rates.

Purpose of the Study:

• To explore the atomic-scale critical threshold for generating bubble-like nuclei at supercritical pressure.
• To characterize this threshold using total energy (kinetic + potential) and molecular dynamics simulations.

Main Methods:

• Molecular dynamics simulations of argon fluid heated by a solid wall above fluid temperature.
• Controlled fluid pressure via a movable piston wall.
• Investigation of pressure, nonuniform heating, and surface wettability effects.

Main Results:

• Established a new criterion for supercritical pseudoboiling: Total Energy (Te) > 0.012 eV at 8 MPa for argon.
• The critical threshold increases with pressure.
• Nonuniform heating and surface wettability influence nucleation site and heat transfer mode (pseudofilm or pseudonucleate) but not the critical threshold.

Conclusions:

• Pseudoboiling at supercritical pressure lacks surface tension, leading to irregular bubble-like structures.
• The study links subcritical and supercritical boiling by explaining pseudoboiling through kinetic and potential energy competition.
• Provides a fundamental understanding of phase transition phenomena across different pressure regimes.