A thermokinetic model for dropwise condensation on a planar substrate with conical pores

Abstract

Within the framework of the classical theory of heterogeneous condensation, a thermokinetic model has been developed for dropwise condensation on a planar substrate with conical pits. The development or the dissolution of the nucleated droplet is accounted due to both interfacial and peripheral mass transfer and by considering various geometric configurations, i.e. formed droplet within the conical pore, at the pore edge, and outside the pore respectively. Along with the principle of exergy maximization, detailed-balance-based kinetic approach has been employed to investigate the influence of the pore size and the substrate wettability on the thermokinetics of droplet nucleation of water vapor. The available energy for droplet formation and the time rate of nucleation are obtained. The twice-nucleation phenomenon is supposed to take place for some particular pore sizes and its thermokinetic trait is different from that obtained from the classical condensation theory. For a given conicity, there is an appreciable amount of reduction in the free energy barrier with increase in the contact angle. The slant height of the conical pit is found to have a great influence in the condensation enhancement or suppression. The barrier reduces considerably when the slant height reduces. These outcomes indicate a physical insight into the context of surface engineering for the promotion or the hindrance of dropwise condensation on real or engineered surfaces.