Vapor-phase transport, surface evolution

The droplet current / calculated by nucleation models represents a limit of initial new phase production. The initiation of condensed phase takes place rapidly once a critical supersaturation is achieved in a vapor. The phase change occurs in seconds or less, normally limited only by vapor diffusion to the surface. In many circumstances, we are concerned with the evolution of the particle size distribution well after the formation of new particles or the addition of new condensate to nuclei. When the growth or evaporation of particles is limited by vapor diffusion or molecular transport, the growth law is expressed in terms of vapor flux equation, given by Maxwell s theory, or... 

There has been considerable attention given to the development of 2 and 3-D numerical models to approximate the coupled two-phase mass and heat transport within unit cells, see [5, 7, 8, 15, 17, 22, 25, 29, 30, 38, 39, 37]. However, these approaches have either not fully resolved the multiphase flow, advecting the liquid as suspended droplets in the gas flow, or used isothermal models in which the vapor and liquid are treated as a combined mixture, or have experienced convergence difficulties for physically reasonable values of the parameters. The majority of the treatments are at steady-state, and none has treated the transient evolution of the free surface separating the two-phase and dry regions in the hydrophobic GDL. 

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