STTR Phase II: Condensation on Gradient Surfaces

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.