Mesoscale model droplets

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. 

The mesoscale models for momentum transfer between phases differ quite substantially depending on the multiphase system under investigation, and different semi-empirical relationships have been developed for different systems. Since the nature of the disperse phase is particularly important, the available mesoscale models are generally divided into those valid for fluid-fluid and those valid for fluid-solid systems. The main difference is that in fluid-fluid systems the elements of the disperse phase are deformable particles (i.e. bubbles or droplets), whereas in fluid-solid systems the disperse phase is constituted by particles of constant shape. Typical fluid-fluid systems for which the mesoscale models reported below apply are gas-liquid, liquid-liquid, and liquid-gas systems. The mesoscale models reported for fluid-solid systems are valid both for gas-solid and for liquid-solid systems. As a general rule, the mesoscale model for Afp should be derived starting from a single-particle momentum balance ... 

Figure 4 Calculation algorithm of mesoscale model with discrete droplets.

The spontaneous emergence of avalanches, droplets and rivulets is very difficult to simulate with classical fluid dynamical models, due to the critical nature (self-organized criticality) and threshold character of these nonlinear phenomena. Therefore, the role of statistical fluctuations in thin-film dynamics cannot be underestimated, especially in the mesoscale. Unlike the classical approaches, we need not introduce any external and artificial perturbations. All phenomena occur spontaneously due to thermal noise inherent in the nonlinearly interacting particle dynamics. 

Multiscale descriptions of particle-droplet interactions in spray processing of composite particles are realized based on Multiphase Computational Fluid Dynamics (M-CFD) models, in which processes such as liquid atomization and particle-droplet mixing spray (macro-scale), particle-droplet collision (mesoscale), and particle penetration into droplet (micro-scale) are taken into account as shown in Fig. 18.52. Thereby, the incorporation efficiency and sticking efficiency of solid particles in matrix particles are correlated with the operatiOTi conditions and material properties. 

Due to the high-computational effort, these calculations are performed only for a relatively short period of real time (in order of seconds). The particle trajectories and the fluid profile obtained by this modeling are transferred to the mesoscale, where the simulations of particle wetting and drying are performed. On the mesoscale two different models are employed. The first model describes droplets as separate objects solving Newtonian equations of motion for each droplet and analyzing coUisions between particles and droplets. These calculations allow to predict the overspray rate The second model is used to calculate the drying of the Uquid from particle... 

On the mesoscale, not only particles have been treated as separate objects, but also the liquid droplets have been represented as discrete elements and their translational and rotational motion in the fluid field has been calculated. To perform modeling of the nozzle zone, following a set of simplifications and assumptions have been carried out ... 

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