STTR Phase I: Condensation on Gradient Surfaces

这个小型企业技术转移一期项目将进行创新的传热研究，涉及润湿性梯度上的滴状冷凝。单是滴状冷凝就显示出比典型的垂直热虹吸管的膜状冷凝增加一个数量级的冷凝传热系数的能力。在梯度表面上凝结的液滴经历不同的接触角，导致液滴在增加润湿性的方向上加速到高速。冷凝液滴两侧接触角的差异是由于冷凝表面局部性质的变化，由低表面能分子的不同表面浓度控制。在梯度表面上冷凝引起的高液滴速度进一步增加了典型液滴冷凝的换热系数。此外，梯度表面不需要重力来从冷凝表面去除液体，从而在水平表面和微重力应用中实现液滴冷凝传热系数值。该项目更广泛的影响/商业潜力在于，该技术将有能力影响各种商业应用中的传热解决方案，在这些应用中，耗电更多的能力与更好的性能并行。在计算机处理行业，笔记本电脑和服务器的解决方案越来越受到散热解决方案的限制。在微重力环境下，梯度表面将取代或增强热管装置中目前使用的毛细力，如轴向沟槽热管和航天器应用的环路加热。目前已经出现了对更高容量热解决方案的需求，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马兰戈尼流引起的液体运动的基本理解。类似的马兰戈尼流的使用，如温度梯度诱导流，是目前微流体应用中流体泵送的许多研究的焦点。

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.