Evaporating jets and phase transition in rarefied conditions

Abstract

This work examines the evaporation and condensation phenomena at small scales, focusing on how surface deformations affect mass and heat transfer under temperature-driven and pressure-driven conditions. The rarefaction effects arising at these scales cannot be accurately captured by the classical continuum theories such as Navier-Stokes-Fourier equations. To address this limitation, the coupled constitutive relations (CCR) are employed to describe the process. The thermodynamically admissible boundary conditions for both partial and complete evaporation and condensation are presented by determining the reciprocity coefficients for the CCR model. The problem is solved using the method of fundamental solutions (MFS), which is a meshless numerical scheme. Numerical results from the MFS are validated with an analytic solution for a circular cross section of an evaporating jet. Furthermore, the effect of cross-sectional deformations on evaporation and condensation is demonstrated by evaluating mass and heat transfer characteristics wherein spherical harmonics are used to generate deformed shapes. An error analysis is performed to showcase the accuracy and convergence of the MFS. The results provide an understanding of the modeling of phase-change phenomena in micro- and nanoscale systems. © 2025 Author(s).