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

喷墨技术允许控制各种流体的微滴的产生和沉积，有机液体、聚合物、介电冷却剂和液态金属。应用包括材料加工、微电子制造和冷却以及表面涂层。100 mm的典型液滴直径意味着非常大的表面体积比，这大大增强了液滴与其周围环境之间的传输现象。然而，目前的温度测量技术的时间和空间分辨率，这是在1毫秒和1毫米的顺序，分别是不足以捕获的瞬态传输现象发生在沉积的早期阶段的微滴在固体表面上在不同的温度。提出的研究的第一个目标是开发一种基于激光的温度测量方法，其时间和空间分辨率分别为1 ms和10 mm。第二个目标是将这种新的测量方法与现有的有限元模型一起应用，该模型是专门为微滴冲击和现有的高速可视化设置而建立的：这种结合的实验和数值技术将提供关于微滴沉积过程中热流、流体流动和相变耦合的深入知识。将研究在较冷表面上的微滴的快速凝固和在热表面上的微滴的沸腾的起始，考虑工程表面粗糙度和涂层的影响。预测和定量模型的界面热导和相变的瞬态行为将制定。

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.