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EE15.1.03 - Steam Condensation Rate Improvement Using Metal Matrix-Hydrophobic Nanoparticle Composites for Sustainable Thermal Power Plant Efficiency Enhancement 
March 29, 2016   2:30pm - 2:45pm

Renewable energy sources are unlikely to completely displace traditional thermal energy generating methods in the foreseeable future. Furthermore, renewables such as solar and wind power require traditional backup systems for windless and/or cloudy days. Consequently, finding routes to increase efficiency of traditional power generating approaches should be considered an integral part of sustainable development. This is not a simple task, since thermal power plants that operate on a steam cycle have been around and continually improved for over a hundred years. Finding routes to passively enhance steam condensation rate, which governs the back-pressure for the steam turbines, is one of the remaining materials-development opportunities in this area. Steam condensers are fundamental components of about 85% of electricity generation plants and 50% of desalination plants installed globally.1 Consequently finding routes to even moderately improve efficiency of the condensation process could have substantial impact on sustainable development.
In this talk we will provide a brief overview of steam condensation fundamentals and how novel materials can be used to enhance efficiency of this phase change process. Since the 1930s, hydrophobization of metal surfaces has been known to increase heat transfer during water condensation by up to an order of magnitude,2 whereby this surface modification switches the condensation mode from filmwise (FWC) to dropwise (DWC). However, use of hydrophobic coatings required to promote DWC introduces an additional resistance to heat flow. Thus, in simplified terms, to increase the total heat transfer rate, thermal resistance introduced by the hydrophobic coating must be significantly smaller than that posed by the water film during FWC. Unfortunately, most hydrophobic coatings suffer from longevity issues. We will review recent material developments in this area (rare earth oxides, grafted polymers, grapheme, and lubricant impregnated surfaces etc.) and durability challenges stemming from thin film nature of these hydrophobic coatings. We will also discuss our recent alternative to these thin film modifiers: metal matrix hydrophobic nanoparticle composites.3 We have recently demonstrated that with properly sized and distributed nanoparticles, such materials can sustainably promote DWC. Furthermore, due to the high thermal conductivity of the matrix, the composites have a potential to be used in bulk-like manner. This could dramatically enhance their longevity as compared to thin film hydrophobic promoters and thus provide a viable route of sustainably enhancing condenser, and with that power plant, efficiency.

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