Numerical investigation on droplet lateral movement in post-dryout region

• Smaller droplets exhibit higher average radial velocities, with deposition velocity decreasing as approaching the wall. • Statistical analysis shows that evaporation halts low-velocity droplets from reaching the wall. • Quantitative analysis reveals that evaporation inhibits droplet deposition while promoting entrainment. • Existing deposition correlations for unheated walls are unsuitable for post-dryout conditions. This paper presents a numerical study of droplet lateral movement and droplet deposition behaviors in the post-dryout region using the Discrete Particle Model (DPM) in ANSYS FLUENT. The investigation focuses on the analysis of droplet lateral movement, including single droplet trajectory, the statistic distribution and average value of droplets radial velocity, and droplet transverse between central and near wall regions. The single droplet trajectory shows the droplet dynamic behavior in the near wall region vividly. The droplet radial velocities are plotted as histogram to display the droplets statistic characteristics. The average value of droplets radial velocities toward the wall are plotted along the radial distance. In addition, to quantitatively display the size and evaporation effect on droplet deposition, three new parameters presenting overall movement behavior, i.e. droplet deposition mass flux, droplet deposition velocity as well as droplet entrainment velocity are introduced and derived from the CFD results. The comparison of results with varying initial droplet size indicates that droplets with smaller sizes exhibit higher average velocities toward the wall. A smaller initial droplet size leads to a higher deposition velocity, lower entrainment velocity, and thus a higher droplet deposition mass flux. The histogram of droplet radial velocities reveals that the droplet evaporation significantly reduces the number of droplets with small radial velocities toward the wall, resulting in a decrease in overall droplet deposition mass flux. Furthermore, through the comparison of overall movement behavior parameters, evaporation not only inhibits droplet motion toward the wall but also noticeably enhances droplet movement away from the wall. This inhibition effect on droplet deposition and enhancement effect on droplet entrainment become more pronounced with increasing evaporation intensity.