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Gewählte Doctoral Thesis:

Siswo Sumardiono (2005): Molecular Simulations of Droplet Evaporation Processes.
Doctoral Thesis, BOKU-Universität für Bodenkultur. UB BOKU obvsg

Data Source: ZID Abstracts
Abstract:
Evaporation processes of droplets are studied by molecular dynamics simulations of pure and mixed Lennard-Jones fluids. Two basically different evaporation mechanisms are considered. a) The evaporation is driven by adiabatic pressure jump without heat transfer to the system. Two physically different initial conditions are used. In the one case a droplet which is in equilibrium with its vapour - a wrapped droplet - is brought into a larger empty box. In the second case a droplet cut out from a liquid - a bare droplet -is brought into vacuum. b) The evaporation is driven by continuous heat transfer. Again, two different cases are treated - evaporation of a droplet surrounded initially by its vapor in equilibrium and evaporation of a bare cold droplet surrounded initially by warm vapor. In both cases heat is transferred from a heat bath surrounding the droplet in some distance from its surface. In the case of evaporation of the bare cold mixture droplet, a third component is taken as warm pure vapour. First, we had to prepare well-defined initial condition states, including definitions of the droplet and vapour particles and the droplet centre. During the evaporation process, calculations of the time dependent number of droplet particles and of several space and time dependent hydrodynamic quantities as the density, the drift velocity as well as the radial, tangential, and total temperature were performed. In case of mixtures, also the composition of the liquid and the vapour and the hydrodynamic quantities for each component were calculated. In the case of pressure drop evaporation starts and after a transition state a new droplet-vapour equilibrium is reached at some lower temperature (temperature at the wet bulb). In case of pressure jump evaporation of the mixture only the more volatile component evaporates. In the case of continuous heat transfer, the density profiles show mostly a transition from a well defined droplet with liquid-vapor interface to a cluster being of interfacial type and finally to a homogeneous gas state. The temperature profiles at a given time show a nearly constant value within the droplets or clusters but strong temperature gradients in the gas. In case of evaporation of a bare cold droplet surrounded by warm vapor we observed cooling down of the droplet at the beginning corresponding to pressure jump evaporation. In the case of mixtures the more volatile particles are evaporated much faster than the solvent particles. In case of a low heat bath temperature the final equilibrium can be again a droplet surrounded by vapour.


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