No abstract

No abstract

We study the role of solid-liquid interface thermal resistance (Kapitza resistance) on the evaporation rate of droplets on a heated surface by using a multiscale combination of molecular dynamics (MD) simulations and analytical continuum theory. We parametrize the nonbonded interaction potential between perfluorohexane (CF) and a face-centered-cubic solid surface to reproduce the experimental wetting behavior of CF on black chromium through the solid-liquid work of adhesion (quantity directly related to the wetting angle). The thermal conductances between CF and (100) and (111) solid substrates are evaluated by a nonequilibrium molecular dynamics approach for a liquid pressure lower than 2 MPa. Finally, we examine the influence of the Kapitza resistance on evaporation of droplets in the vicinity of a three-phase contact line with continuum theory, where the thermal resistance of liquid layer is comparable with the Kapitza resistance. We determine the thermodynamic conditions under which the Kapitza resistance plays an important role in correctly predicting the evaporation heat flux.

Electrocoalescence of aqueous droplets in oil emulsions is commonly contemplated for enhancing separation. High voltage electric fields can induce charges to drops evoking merging of adjacent droplets. The newly formed larger drops then sink faster in gravitational common settlers. Therefore, separation performance of an electrostatic coalescer is strictly linked to characteristics of the electric field and properties of the liquid–liquid system. In this work, the coalescence performance of water droplets sinking in dodecane at a pulsed DC electric field is investigated. An experimental setup allowing the simultaneous injection of similar sized drops, setting of voltage and pulsation frequency, and particle tracking at high frame rate and resolution is designed. The generated data are used to check the validity of modeling approaches for drag, dipole–dipole forces, and film-thinning. Furthermore, CFD simulations are carried out using a volume of fluid method tracking the interfaces between the two phases

3D Kinetic Monte Carlo (KMC) simulations have been carried out on the epitaxial growth of the silicon (100)2×1 surface as a function of surface temperature (570‐870 °C). The KMC model explicitly takes into account the anisotropy of the silicon (100)2×1 surface and the interaction of neighboring sites as a reaction event at a given surface site not only depends on the chemical nature of the site itself but also on steric factors and the local environment. Thus the model includes data about the local structure of the surface, the nature of the surface adatoms and their neighbors, the kinetic reaction parameters, and the incident precursor atoms. Reaction probabilities are calculated with the Arrhenius equation, kinetic parameters are taken from experimental and calculated data from the literature. First estimations are given for missing values. Silane is assumed to be the only gas‐phase reactant on the surface, coupling with the gas phase is carried out by silane partial pressure. For the first time a really complex algorithm comprehending 12 different surface sites and more than 100 reactions such as silane adsorption, SiHx decomposition and diffusion of adsorbed species is presented. The model provides a good fit to experimental observations and theoretical knowledge. Experimental data of growth rate and hydrogen coverage can be reproduced (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)