Friday, October 13, 2023
2:00pm-3:00pm
Mechanical Engineering Building, MC102
5 King's College Road
Interested members of the U of T community who would like to attend the seminars can email Kendra Hunter at hunter@mie.utoronto.ca
Professor Gang Chen
Massachusetts Institute of Technology (Department of Mechanical Engineering)
Photomolecular And Thermal Evaporation at Water-Air Interface
Abstract
Bulk water does not absorb well visible light: green light at 0.5 mm can propagate 40 m in bulk water. We believe, however, that photons in the visible spectrum can cleave off water molecular clusters directly from the water-vapor interfaces, in analogy to the photoelectric effect discovered by Hertz and explained by Einstein. We call this process the photomolecular effect. The cleaved clusters can recondense back, leading to absorption and heating, or escape the surface, leading to evaporation rate exceeding the limit of thermal evaporation. We first show experimental evidence supporting such photomolecular effect: partially wet hydrogels become absorbing despite neither the polymers nor water absorb in the visible spectrum, solar-interfacial evaporation from even pure hydrogels without black absorbers can exceed the thermal eaporation limit, wavelength dependence of evaporation rates, and peculiar vapor temperature distributions. We then characterize the photomolecular effect at pure water-air interface by probing water and vapor using a variety of techniques. Temperature measurements in the vapor phase also lead us to study temperature discontinuity at water-vapor interface, and reformulate pure thermal evaporation problem, leading to new insights on this ubiquitous phenomenon.
Biography
Gang Chen is the Carl Richard Soderberg Professor of Power Engineering at Massachusetts Institute of Technology (MIT). He served as the Department Head of the Department of Mechanical Engineering at MIT from 2013 to 2018. He obtained his PhD degree from the Mechanical Engineering Department at UC Berkeley. He was a faculty member at Duke University and UCLA, before joining MIT in 2001. He received an NSF Young Investigator Award, an R&D 100 award, an ASME Heat Transfer Memorial Award, an ASME Frank Kreith Award in Energy, a Nukiyama Memorial Award by the Japan Heat Transfer Society, a World Technology Network Award in Energy, an Eringen medal from the Society of Engineering Science, and the Capers and Marion McDonald Award for Excellences in Mentoring and Advising from MIT. He is a fellow of American Association for the Advancement of Science, the American Physical Society, The American Society of Mechanical Engineers, and the Guggenheim Foundation. He serves on the board of the Asian American Scholar Forum (aasforum.org). He is an academician of Academy Sinica, a fellow of the American Academy of Arts and Sciences, a member of the US National Academy of Engineering and US National Academy of Sciences.
MIE’s Distinguished Seminar Series features top international researchers and leading experts across major areas of Mechanical Engineering and Industrial Engineering. The speakers present about their latest research and offer their perspectives on the current state of their field. The seminars are part of the program requirements for MIE Master of Applied Science and PhD students. The Distinguished Seminar Series is coordinated for 2023-2024 by Associate Professor Eric Diller.
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