Coupling the High Resolution of Laser Measurements and Finite-Element Simulations to Understand Transport Phenomena during Microdroplet Deposition

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Ink-Jet technology allows the controlled generation and deposition of microdroplets of a wide range of fluids, e.g., organic liquids, polymers, dielectric coolants and liquid metals. Applications include materials processing, microelectronics manufacturing and cooling, as well as surface coatings. A typical droplet diameter of 100 mm implies a very large surface to volume ratio, which drastically enhances transport phenomena between the droplet and its surroundings. However, the temporal and spatial resolutions of current temperature measurement techniques, which are on the order of 1 ms and 1 mm, respectively, are not sufficient to capture the transient transport phenomena occurring during the early stages of the deposition of a microdroplet on a solid surface at a different temperature. The first objective of the proposed research is to develop a laser-based temperature measurement method with temporal and spatial resolutions on the order of 1 ms and 10 mm, respectively. The second objective is to apply this novel measurement together with an existing finite-element model built particularly for microdroplet impact and an existing high-speed visualization setup: this combined experimental and numerical technique will provide in-depth knowledge on the coupling of the heat flow, fluid flow and phase change during microdroplet deposition. The rapid solidification of a microdroplet on a colder surface and the initiation of boiling of a microdroplet on a hot surface will be investigated, with consideration of the influence of engineered surface roughness and coatings. Predictive and quantitative models for the transient behavior of the interfacial thermal conductance and phase change will be formulated.