Evolution of transient cluster/droplet size distribution in a heterogeneous nucleation process

Abstract

The transient nucleation size distribution model was introduced into a water vapor condensation system to investigate the kinetics of the initial condensation stage. It was proven that the growth/decay of clusters was significantly affected by cluster size and contact angles of the condensation surface. As the cluster size increased, the cluster surface area exposed to vapor was also increased, and the attachment/detachment frequencies increased accordingly. As the contact angle decreased to a certain value, the attachment frequency became larger than the detachment frequency, which is beneficial for the growth of clusters. The evolution of cluster/droplet size distribution was also investigated. The results indicated that the transient cluster size distribution of the heterogeneous process translates from a monotonic decreasing to a unimodal distribution with time. Peak value of cluster/droplet population can be observed for a sufficiently long time, and the size distribution curve is found to be close to a lognormal distribution, which is distinctly different from the homogeneous equilibrium distribution. The peak value in the size distribution curve shifts to larger cluster sizes with time, and the absolute value decreases accordingly. It is very similar to the reported experimental results of micron scale droplets, revealing that the subsequent experimental phenomenon at macroscopic scale was the direct result of the further development of the initial cluster/droplet size distribution. The present study investigated the effect of contact angle on the growth/decay of clusters and analyzed the mechanism of the evolution of the cluster/droplet size distribution from the viewpoint of kinetics.