The growth of condensed nanodroplets in electric fields: A molecular dynamics study

Abstract

Electric fields (E-Fields) can promote droplet detachment and improve dropwise condensation. Since droplet growth is dominant in the dropwise condensation cycle, the influence of the applied electric field on the growth of condensed droplets is worth exploring. In this work, the effect of molecule orientation polarization in the electric field on the growth of condensed nanodroplets is studied via molecular dynamics simulation. The results show that when the size of a growing cluster reaches a critical size Rc, the orientation polarization of water molecules within the cluster significantly increases. The orientation polarization is shown to reduce the interaction between water molecules, and the condensed molecules are easier to escape. Thus, the reduced interaction between water molecules hindered the growth of condensed clusters. Especially when the cluster size exceeds Rc, the increased orientation polarization makes this hindrance more pronounced. However, the morphology of the cluster simultaneously transforms from ellipsoidal to needle-like at the critical size, and the shape deformation of the cluster can also affect the growth rate. When the cluster size is larger than Rc, a vertical E-Field stretches the condensed cluster perpendicular to the substrate, which decreases the solid-liquid interfacial area of the cluster. The reduction of solid-liquid interfacial area and the reduced interaction between water molecules jointly hinder the growth of condensed clusters. On the contrary, needle-shaped deformation induced by parallel electric fields can increase the contact area between the cluster and the substrate. Therefore, the increased solid-liquid interface area can compensate for the negative effect of orientation polarization on the growth. Besides, when the cluster size is smaller than Rc, the growth rate is mainly related to the polarization-induced weakened interactions between molecules. Thus, in stage R < Rc, both vertical and parallel electric fields hinder the growth.