Soo Distinguished Lecture features MIT's Chen

Professor Gang Chen was the honored speaker at the Spring 2025 Yunchuan Aisinjioro-Soo Distinguished Lecture, held March 24 in the National Center for Supercomputing Applications (NCSA) Auditorium.

Chen is the Carl Richard Soderberg Professor of Power Engineering in the Department of Mechanical Engineering at Massachusetts Institute of Technology (MIT). His lecture was titled “Evaporation Peculiarities: Photomolecular Effect and Evaporative Refrigeration Effect.”

Abstract: This talk will discuss two peculiar effects we recently discovered: the photomolecular effect and the evaporative refrigeration effect. To explain super-thermal solar-interfacial evaporation from hydrogels and other porous materials, we hypothesize that photons can directly cleave off water clusters at the liquid-vapor interface in a way similar to the photoelectric effect, which we call the photomolecular effect. We carried out over 20 different experiments on both hydrogel and a water-air interface to prove the existence of this effect. The photomolecular effect could resolve an over 70-year puzzle in atmospheric science: some experiments reported more cloud absorption than theory could predicts. We believe that the photomolecular effect should happen widely in nature, from clouds to fogs, ocean to soil surfaces, and plant transpiration, and can also lead to new applications in energy and clear water. Our studies on photomolecular evaporation also led us to investigate peculiarities in thermal evaporation. At an evaporating interface, a temperature discontinuity exists between the liquid and the vapor sides, which was predicted by theories and observed in some experiments. However, the existing theories cannot explain experiments. We develop a new interfacial condition that can be used to couple transport on both sides of the interface, leading to agreements between theory and experiments. Our modeling reveals the existence of a new refrigeration effect: the vapor temperature can drop below that of the liquid film and in fact, lower than even the condensing surface temperature. This effect has yet to be confirmed experimentally and may find applications in air-conditioning and refrigeration.

From 2013 to 2018, Chen served as head of the Department of Mechanical Engineering at MIT, where he has been on the faculty since 2001. He is a fellow of the American Association for the Advancement of Science, the American Physical Society, The American Society of Mechanical Engineers, and the Guggenheim Foundation. He is an academician of Academy Sinica, a fellow of the American Academy of Arts and Sciences, and a member of the U.S. National Academy of Engineering and the U.S. National Academy of Science. 

The Yunchuan Aisinjioro-Soo Distinguished Lecture was established in 1992 by Professor Shao Lee Soo and his wife, Hermia. Professor and Mrs. Soo sought to perpetuate the memory of his mother, Yunchuan Aisinjioro-Soo (1899-1991). Born Princess Shansji of Aisinjioro, the last Royal House of China, she took the pen name Yunchuan and became an accomplished poet and artist. Throughout the turmoil of revolution and war, she steadfastly believed that the way for the family to serve the people is through the education of its children.

Two of the Soos’ three children – Lydia Soo and Shirley Soo – attended the lecture, along with other special guests, including Y.K. Wen, a professor emeritus of civil and environmental engineering at Illinois and friend of the Soo family.