Droplet evaporation: A molecular dynamics investigation

Molecular dynamics simulations are used to model the evaporation of a Lennard-Jones argon nanodroplet into its own vapor for a wide range of ambient temperatures and ambient pressures. The transitions from (i) high to low Knudsen number evaporation and (ii) subcritical to supercritical evaporation are observed. At a low ambient pressure of 0.4 MPa, the initial droplet Knudsen number is 1 and the droplet diameter decreases linearly with time, consistent with kinetic theory predictions. For a moderate ambient pressure of 3.0 MPa, the initial droplet Knudsen number is 0.1 and the square of the droplet diameter decreases linearly with time. For a high ambient pressure of 6.1 MPa, the evaporation is supercritical and the number of atoms in the droplet decreases linearly for the majority of the droplet lifetime. A technique is introduced to maintain a constant ambient pressure over the droplet lifetime, allowing for the observation of the influence of the ambient conditions on the droplet surface temperature. When the ambient pressure is greater than or equal to 1.4 times the critical pressure, the droplet surface temperature reaches the critical temperature and the evaporation is supercritical. Below this ambient pressure, the droplet surface temperature reaches a pseudowet-bulb condition.