STTR Phase II: Condensation on Gradient Surfaces

这个小型企业技术转移研究(STTR)第二阶段项目提出了创新的热传递研究，涉及润湿性梯度上的滴状冷凝。仅滴状冷凝就显示出比垂直热虹吸管的典型的气膜冷凝提高冷凝换热系数一个数量级的能力。在梯度表面上凝结的液滴会经历不同的接触角，导致液滴在润湿性增加的方向上加速到高速。凝聚液滴相对两侧接触角的差异是由于凝聚表面的局部性质不同，受低表面能分子表面浓度的不同控制。与典型的滴状冷凝相比，梯度表面冷凝引起的较高的液滴速度进一步增加了换热系数。此外，梯度表面不需要重力来从冷凝表面除去液体，从而在水平表面和微重力应用中实现滴状冷凝换热。在这份提案中，第一阶段展示的技术将被集成到适用于电子冷却的蒸汽室热传递设备中。该项目将在热管理行业感受到更广泛的影响/商业潜力。具体地说，采用这一创新将显著提高蒸汽室的热性能，从而节省成本，并在许多行业提高性能。在计算行业中，笔记本电脑和服务器的解决方案越来越受到散热问题的限制。在微重力环境中，这些新的梯度表面将取代或增强目前用于通信卫星应用的热管设备中的毛细作用力，例如轴向开槽热管和环状热管。在核工业中，更高效的冷凝直接提高了电转换效率。对更高容量的散热解决方案的需求已经存在，随着商业实体和政府机构扩大其能力并要求更大的散热，这种需求只会增加。这项开发工作还将加强对由于表面梯度和类似的Marangoni流动引起的液体运动的基本了解，这将对各个领域产生影响，包括与微流体应用中的流体泵送有关的研究。

This Small Business Technology Transfer Research (STTR) Phase II project proposes innovative heat transfer research involving dropwise condensation on a wettability gradient. Dropwise condensation alone has shown the ability to increase condensation heat transfer coefficients by an order of magnitude over film condensation, typical of vertical thermosyphons. Droplets condensing on a gradient surface experience different contact angles, causing the droplets to accelerate to high velocities in the direction of increased wettability. The difference in contact angle on opposite sides of the condensing droplets is due to locally varying properties of the condensing surface, controlled by varying surface concentrations of molecules with low surface energy. The higher droplet velocities caused by condensing on the gradient surface further increases the heat transfer coefficient over typical dropwise condensation. Furthermore, the gradient surface does not require gravity to remove liquid from the condensing surface, enabling dropwise condensation heat transfer on horizontal surfaces and in microgravity applications. In this proposal, the technology demonstrated in Phase I will be integrated into a vapor chamber heat transfer device suitable for electronics cooling.The broader impact/commercial potential of this project will be felt in the thermal management industry. Specifically, incorporating this innovation will enable significantly improved thermal performance in vapor chambers, leading to cost savings and allowing improved performance in a number of industries. In the computing industry, solutions for notebook computers and servers are becoming increasingly limited by thermal issues. In micro-gravity environments, these new gradient surfaces will replace or enhance the capillary forces currently used in heat pipe devices, such as axially grooved heat pipes and loop heat pipes, for communication satellite applications. In the nuclear industry, more efficient condensation directly increases electrical conversion efficiency. There is already a demand for higher capacity thermal solutions, and this demand will only increase as commercial entities and government agencies expand their capabilities and demand greater thermal dissipation. This development effort will also enhance the fundamental understanding of liquid movements due to surface gradients and similar Marangoni flows, which will have an impact in various fields, including research related to fluid pumping in micro-fluidic applications.