Manipulation of Solid-Liquid-Vapor Phase Change for Energy Applications
Phase change phenomena (evaporation and condensation, melting and freezing) play a dominant role in a myriad of energy technologies such as thermal energy storage, solar-thermal energy generation, fossil power plants, microelectronics thermal management systems, and thermal energy-based water desalination. In spite of enormous progress, the thermal conductance of phase change heat transfer technologies is still at least two orders of magnitude lower than the theoretical limit given by kinetic theory. We are conducting fundamental investigations to close the gap between this ideal and reality.
Dropwise condensation has been significantly researched since its discovery in the 1930s due to its superior heat transfer performance over conventional filmwise condensation. However, recent studies have shown that a combination of high surface roughness and hydrophobic surface chemistry can result in jumping droplet condensation. This decrease in the droplet size on a surface results in order-of-magnitude increases in heat transfer coefficients during vacuum steam conditions. We are working in collaboration with Nelumbo on DOE's Office of Fossil Energy-funded project to improve the steam-side heat transfer coefficient of steam condensers using Nelumbo’ inorganic coatings by 400%, resulting in a 26% increase in the overall conductance (U value) of the condenser.
These efficiency gains could be used to reduce the cooling water flow by up to 39%, resulting in savings of over 78,000 gallons of water per minute for a 500 MW steam turbine and over $6M savings annually in a coal fired power plant. Unlike other coatings, these surface modifications are durable inorganic materials that are chemically bound to the surface of the tubes with improved performance over dropwise coatings. Nelumbo currently apply coatings through a dip coating procedure that can be scaled and integrated with the installed steam condenser to coat the shell-side components. The objective of the project is to build upon the capabilities of the current Nelumbo coatings for commercial heat exchangers as well as grasp a better understanding of the wettability and the presence of liquid-phase change phenomena in condensing droplets.
With global populations increasing, expanding urbanization and climate change impacts leading to more frequent heatwaves and seasonal temperatures rises, the world will demand far more cooling and produced cold in the decades ahead. Among all the cold energy utilizations, water freezing is necessary for numerous important human activities including food reserving, medical treatment, and building cooling. However, two common phenomena during freezing, i.e. supercooling and ice adhesion, limit its operating efficiency. To address the issue, we put forward a novel scheme combining of electro-freezing and passive de-icing and do an optimization of the freezing curve. By doing the experimental designing and mechanism exploring, we are trying to extend the freezing process into broader applications including high-efficiency thermal storage and water treatment.