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

喷墨技术允许受控地产生和沉积各种流体的微滴，例如有机液体、聚合物、介质冷却剂和液态金属。应用包括材料加工、微电子制造和冷却以及表面涂层。典型的液滴直径为100毫米，意味着非常大的表面积与体积比，这极大地加强了液滴与其周围环境之间的传输现象。然而，当前温度测量技术的时间和空间分辨率分别为1ms和1 mm，不足以捕捉到在不同温度下微滴在固体表面沉积的早期阶段发生的瞬时输运现象。该研究的第一个目标是开发一种基于激光的温度测量方法，其时间分辨率和空间分辨率分别为1ms和10 mm。第二个目标是将这种新的测量方法与专门为微滴碰撞建立的现有有限元模型和现有的高速可视化装置一起应用：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、流体流动和相变的耦合的深入知识。考虑到工程表面粗糙度和涂层的影响，我们将研究微滴在较冷表面上的快速凝固和微滴在热表面上的沸腾。将建立界面热导和相变的暂态行为的预测和定量模型。

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.