STTR Phase I: Condensation on Gradient Surfaces

这个小型企业技术转移第一阶段项目将进行创新的换热研究，包括润湿梯度上的滴状冷凝。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系数值。该项目更广泛的影响/商业潜力是，该技术将能够影响各种商业应用中的热传输解决方案，在这些应用中，散热能力与更好的性能是平行的。在计算机处理行业中，用于笔记本计算机和服务器的解决方案越来越受到散热解决方案的限制。在微重力环境中，梯度表面将取代或增强目前在热管设备中使用的毛细作用力，例如用于航天器应用的轴向凹槽热管和环路加热器。对更高容量的散热解决方案的需求已经存在，随着商业公司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。这项研究将进一步加深对由于表面梯度和类似的Marangoni流引起的液体运动的基本了解。类似Marangoni流的应用，如温度梯度诱导流，目前是许多关于微流体应用中流体泵送的研究重点。

This Small Business Technology Transfer Phase I project will undertake 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 coefficient values on horizontal surfaces and in microgravity applications. The broader impact/commercial potential from this project is that the technology will have the ability to impact heat transfer solutions in various commercial applications where the ability to dissipate more power is parallel to better performance. In the computer processing industry, solutions for notebook computers and servers are becoming increasingly limited by the thermal solution. In micro-gravity environments a gradient surface will replace or enhance the capillary forces currently used in heat pipe devices, such as axially grooved heat pipes and loop heats for spacecraft applications. There is already a demand for higher capacity thermal solutions, and this demand will only increase as commercial companies and government agencies expand their capabilities and demand greater thermal dissipation. This research will further the fundamental understanding of liquid movements due to surface gradients and similar Marangoni flows. Uses of similar Marangoni flows, such as temperature gradient induced flows, are currently the focus of many studies regarding fluid pumping in microfluidic applications.