Pushing Boundaries of Thermal Transport and Sustainable Energy: From First Principles Predictions to Scalable Applications

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Abstract: This talk will overview our recent innovations in thermal transport and sustainable energy, by pushing the boundaries ranging from fundamental first principles predictions to scalably manufactured systems. The first part of the talk will cover predictive first principles and molecular dynamics simulations of thermal conductivity and optical (or thermal radiative) properties. In particular, we establish four-phonon scattering as an unexpected significant mechanism affecting thermal conductivity of nearly all materials at high temperature, and 2D materials, low thermal conductivity materials, and certain high-thermal conductivity materials even at room temperature.1 In addition, four-phonon scattering can have significant or leading role in determining infrared optical properties of dielectrics.2 For complex crystals, the conventional phonon mean free path concept is insufficient, and we propose a two-phonon transport theory to better describe their thermal transport.3 We further show that machine learning can be used to dramatically accelerate the predictive design of energy nanomaterials.4 The second part of the talk will cover our development of the first commercial-like particle-matrix radiative cooling paint that can cool below the ambient temperature under direct sunlight.5 It is achieved via several approaches distinct from commercial paints: the use of the wide bandgap CaCO3 fillers, a high particle volume concentration of 60%, and a broad size distribution. Radiative cooling paints can have broad implications from saving energy to combatting climate change.6 The talk will close by exploring future directions and collaboration opportunities.

1. Feng et al., Phys. Rev. B 96, 161201(R) (2017).  2. Yang et al., Phys. Rev. B 101, 161202(R) (2020).  3. Luo et al., Nat. Commun. 11, 2554 (2020).  4. Chowdhury et al., Nano Energy 69, 104428 (2020).  5. Li et al, Cell Rep. Phys. Sci. 1, 100221 (2020). 6. BBC NEWS

Short bio: Dr. Xiulin Ruan is a professor in the School of Mechanical Engineering and Birck Nanotechnology Center at Purdue University.  He received his B.S. and M.S. from the Department of Engineering Mechanics at Tsinghua University, in 2000 and 2002 respectively. He then received an M.S. in electrical engineering in 2006 and Ph.D. in mechanical engineering in 2007 from the University of Michigan at Ann Arbor, before joining Purdue. His research and teaching interests are in predictive simulations, scalable manufacturing, and multiscale characterizations of thermal transport materials and systems. He received the NSF CAREER Award, Air Force Summer Faculty Fellowship, ASME Heat Transfer Division Best Paper Award, the inaugural School of Mechanical Engineering Outstanding Graduate Student Mentor Award, and was named a University Faculty Scholar of Purdue University and an ASME Fellow, among his honors. He currently serves as an associate editor for ASME Journal of Heat Transfer.