The Interaction between Drops and Solidification Front in Presence of Marangoni Effect
- Paper number
IAC-05-A2.2.04
- Author
Ph.D. Fabrizio Nota, University of Naples "Federico II", Italy
- Coauthor
Prof. Raffaele Savino, University of Naples "Federico II", Italy
- Coauthor
PhD Stefano Fico, University of Naples "Federico II", Italy
- Year
2005
- Abstract
The behaviour of drops in non isothermal liquids with solidification front has been experimentally investigated using transparent model fluids and optical diagnostic techniques. The experiments have been performed using Cyclohexane (melting point equal to 6.5°C) as external matrix and Fluorinert drops. In presence of a temperature gradient, the Marangoni effect at the drop liquid interface affects the drop/solidification front interaction. Preliminary experiments have been carried out to measure the interfacial tension of the liquid-liquid system at different temperatures and to study the fundamental behaviour of a single drop close to the melting front, in presence of a temperature gradient. Heating the system from above and cooling from below, the melting front exhibits a relevant shape deformation as a consequence of the surface tension-driven convection around the drop. A systematic analysis has been carried out to investigate the phenomenon, measuring the solidification front deformation and the convective velocities around droplets of different sizes. The convective motions have been visualised using particle tracers with average size of 30 mum and a background illumination system. Simulations have been developed at the experimental conditions, obtaining a good experimental/numerical correlation. The second part of the study has been focused on the investigation of the interaction between free Fluorinert droplets and a liquid-solid interface, translating a horizontal cuvette between a fixed temperature gradient, with relative speed in the range 0.5-5 mum/s. The experiments pointed out that, under particular conditions, when the relative distance between the droplets and the melting front is of the order of the drop radius, a stable layer of liquid Cyclohexane, of the order of magnitude of hundreds of microns, is formed between the drops and the solidification front, thus preventing their engulfment in the solid. This experimental evidence supports the assumption, made by the authors in previous works, that a “pushing force” is induced by Marangoni effect when the droplets approach the solidification front. Numerical simulations are performed to provide further explanation and correlations with the experimental results.
- Abstract document
- Manuscript document
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