Evaporation, droplet multicomponent

A multicomponent gas flow contains a uniform distribution of small droplets of an organic solvent called A. The droplets have a diameter d and a number density Q [m-3]. The solvent evaporation rate m"k (kg/s-m2) depends on the gas-phase concentration of A. It may be assumed that the volume occupied by the droplets is negligible. 

The General Discussion of the previous section is equally applicable here, except now proper multicomponent descriptions of the gas-phase transport and the interfacial phase change should be used (50,51, 52). By assuming the gas-phase reactions are again confined to a flame-sheet where the reactants are consumed in a species-weighted stoichiometric proportion, explicit expressions can be derived (50) for y, Tf, H, and the fractional mass evaporation rate of the i species, as functions of the temperature and vapor concentration at the droplet surface. 

Recently it was experimentally proven that the highest yield of nanoparticles of different substances, including semiconductor and magnetic ones, is obtained in low pressure spray pyrolysis of special multicomponent solutions [1], During this pyrolysis micron size droplets of the multicomponent aqueous solution evaporate in a low pressure aerosol reactor. Additionally these droplets often have solid precursors of nanometer size, so we can consider every droplet as a colloidal solution. 

For free molecular regime the mathematical model of evaporative cooling of multicomponent droplet with two volatile components has been described in [3]. We use this mathematical model as the background. Additionally, the equation describing the change of a nanoparticle radius R due to diffusion transfer of a soluble impurity is ... 

In contrast to sublimation in freeze-drying, evaporation of a solvent is straightforward but may lead to less homogeneity for example, if a multicomponent solution is slowly evaporated, the various constituents crystallize nonuniformly. Thus, the goal of evaporative techniques is to break the solution into small droplets to minimize the volume over which segregation can take place as well as to maximize the surface area for evaporation and then evaporate the solvent as rapidly as possible to quench in the homogeneity of the solution. 

Given T, the expression for is closed, thereby fixing the mass-transfer rate. The discussion above is applicable to single-component droplets. In many applications, the liquid/gas phase will contain multiple chemical species, for which additional internal coordinates will be necessary in order to describe the physics of evaporation (Sazhin, 2006). In the context of a single-particle model for a multicomponent droplet, the simplest mesoscale model must include the particle mass Mp, the component mass fractions Yp and Yf, and the temperatures Tp and Tf. 

A. M. Lippert and R. D. Reitz. Modeling of multicomponent fuels using continuous distributions with applications to droplet evaporation and sprays. SAE Paper 972882, 1997. 

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