ARTICLE:

• SPREADING AND SOLIDIFICATION OF DROPLETS IMPACTING ON A COLD SUBSTRATE  download article

F. Loghmari
FAST − CNRS, Campus Universitaire, Orsay, France

N. Ferguen
SPCTS − ENSIL, 16 rue Atlantis, Limoges, France

Armelle Vardelle
University of Limoges, Laboratoire Sciences des Procédés Céramiques et de Traitements de Surface, ENSIL,16 rue d'Atlantis, 87068 LIMOGES Cedex, France

Dominique Gobin
Universite Pierre et Marie Curie-Paris 6, Universite Paris-Sud, CNRS, F-91405, Lab FAST, Orsay F-91405, France

ABSTRACT

The dynamics of droplet spreading on a substrate determines the morphology of the resulting splat. Isothermal spreading has been widely studied under this aspect, and the modelling of the flattening mechanism is well understood. Still the full simulation of the process depends on the a priori knowledge of interface properties, such as wettability, or the dynamic contact angles. In a number of processes where the dynamic problem is coupled to heat transfer and solidification, other phenomena may be implied. In the absence of phase change first, the quality of the contact (the "contact resistance") is essential for describing the heat flux at the splat/substrate interface and the spreading process itself depends on the temperature variation of transport properties such as viscosity. If solidification is involved, the full coupling between thermal resistance to heat extraction, phase change and interface characteristics is still challenging problem.
This paper presents a numerical study of splat formation using a model that makes it possible to investigate the cooling and solidification of millimeter-size metallic droplets on steel substrates, implemented in the Simulent Drop^® research code. The numerical model solves the governing equations for conservation of mass, momentum and energy and the free surface of the spreading material is tracked using a volume-of-fluid approach, and it accounts for heat transfer to the substrate and equilibrium solidification of the liquid droplet during spreading. The effect of the substrate and particle parameters at impact on splat shape and cooling rate is investigated in the paper, and needs for further experiments and model developments are identified.

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