Thursday, March 14, 2013
Mechanical and Civil Engineering Seminar
Nanoengineered Surfaces for Efficiency Enhancements in Energy and Water
Kripa Varanasi, Professor, Mechanical Engineering, Massachusetts Institute of Technology
Thermal-fluid-surface interactions are ubiquitous in multiple industries including Energy, Water, Agriculture, Transportation, Electronics Cooling, Buildings, etc. Over the years, these systems have been designed for increasingly higher efficiency using incremental engineering approaches that utilize system-level design trade-offs. These system-level approaches are, however, bound by the fundamental constraint of the nature of the thermal-fluid-surface interactions, where the largest inefficiencies occur. In this talk, we show how surface/interface morphology and chemistry can be engineered to fundamentally alter these interactions in a wide range of thermal-fluid processes including, droplet impact, condensation, boiling, and freezing. We study the wetting energetics and wetting hysteresis of droplets in an Environmental SEM (ESEM) as a function of surface texture and surface energy and establish various wetting regimes and conditions for wetting transitions. We extend these concepts to dynamic wetting and establish optimal design space for droplet shedding, impact resistance, and contact time. We then present the behavior of surfaces under phase change, such as condensation, and freezing at both macroscale and microscale (using ESEM) and find their non-wetting properties can be compromised due to nucleation of water or frost within texture features. Based on these insights we introduce lubricant-impregnated surfaces that can result in two to three orders of magnitude reductions in ice adhesion and promote dropwise condensation. We discuss unconventional contact line morphology, thermodynamics and dynamics of droplet shedding on these surfaces and show how even complex fluids like ketchup, mayonnaise, and jelly slide off the surface easily. Finally, we discuss the influence of electronic structure on interfacial wetting interactions and use these insights to develop new class of ceramic materials that are intrinsically hydrophobic. Manufacturing approaches, robust materials, and applications of nanoengineered surfaces in various energy, water, and transportation systems including oil & gas (flow assurance and energy efficiency), turbines, power and desalination plants, and electronics cooling will be highlighted.