Presenter Information

Yi Zheng, University of Rhode Island

Location

Cherry Auditorium, Kirk Hall

Start Date

2-5-2015 1:00 PM

Description

The ability to control the radiative properties of objects is of great interest in diverse areas like solar and thermophotovoltaic energy conversion, selective thermal emission and absorption, and camouflage in military applications. Thermal radiation at the nanometer scale is significantly different from classical or macroscopic radiative energy transport since near-field effects such as interference, diffraction, and tunneling of surface waves play a significant role.

My talk will focus mainly on small-scale energy, entropy and momentum transfer via electromagnetic waves, especially due to thermal and quantum fluctuations. A dyadic Green’s function formalism has been developed to determine near-field radiative energy and momentum transfer between objects of arbitrary shapes and sizes. Momentum transfer due to electromagnetic fluctuations is responsible for van der Waals and Casimir forces, which are important in many different fields such as adhesion and stiction of materials, bioengineering, and phase change heat transfer. I will talk about how we model van der Waals forces, and show how my work provides a new interpretation, and a better understanding, of this historical problem. In addition, entropy associated with near-field radiative transfer has been studied for the first time. It can be used to determine the maximum work that can be extracted and a thermodynamic limit of energy conversion efficiency that can be obtained in near-field thermal radiation. Experimental investigation will focus on the thermal and optical properties of 2D or 3D nanostructured materials, and it leads to new types of thermophotovoltaic solar cells and selective thermal emitters using metamaterials and nanoparticles. Small-scale thermal transport has shown great potential and applications for use in manipulating macroscale energy systems and energy harvesting.

Speaker Bio

Dr. Yi Zheng is an assistant professor of mechanical engineering at the University of Rhode Island. He leads the Micro and Nanoscale Energy Laboratory, which emphasizes the study of nanoscale thermal transport phenomena, van der Waals/Casimir interactions, thermal, optical and mechanical properties of nanostructured materials (e.g. nanoparticle-nanofiber composites, metallic or dielectric thin films, 2D/3D periodic grating structures), and their applications in thermal energy conversion and energy harvesting systems, thermophotovoltaic solar cell, highly thermal conductive nanowires, and wavelength selective thermal emitters/absorbers.

Dr. Zheng received his Ph.D. and M.S. in mechanical engineering from Columbia University in 2014 and 2011, and B.S. in mechanical engineering from Tsinghua University in 2009. He serves as reviewer for peer-reviewed journals, such as Physical Review A & B, Applied Physics Letters, Journal of Heat Transfer, and as topic/session chair at conferences, such as ASME 2013 Summer Heat Transfer Conference and ASME 2014 IMECE Conference.

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Feb 5th, 1:00 PM

Near-field Radiative Energy, Entropy and Momentum Transfer in Fluctuational Electrodynamics

Cherry Auditorium, Kirk Hall

The ability to control the radiative properties of objects is of great interest in diverse areas like solar and thermophotovoltaic energy conversion, selective thermal emission and absorption, and camouflage in military applications. Thermal radiation at the nanometer scale is significantly different from classical or macroscopic radiative energy transport since near-field effects such as interference, diffraction, and tunneling of surface waves play a significant role.

My talk will focus mainly on small-scale energy, entropy and momentum transfer via electromagnetic waves, especially due to thermal and quantum fluctuations. A dyadic Green’s function formalism has been developed to determine near-field radiative energy and momentum transfer between objects of arbitrary shapes and sizes. Momentum transfer due to electromagnetic fluctuations is responsible for van der Waals and Casimir forces, which are important in many different fields such as adhesion and stiction of materials, bioengineering, and phase change heat transfer. I will talk about how we model van der Waals forces, and show how my work provides a new interpretation, and a better understanding, of this historical problem. In addition, entropy associated with near-field radiative transfer has been studied for the first time. It can be used to determine the maximum work that can be extracted and a thermodynamic limit of energy conversion efficiency that can be obtained in near-field thermal radiation. Experimental investigation will focus on the thermal and optical properties of 2D or 3D nanostructured materials, and it leads to new types of thermophotovoltaic solar cells and selective thermal emitters using metamaterials and nanoparticles. Small-scale thermal transport has shown great potential and applications for use in manipulating macroscale energy systems and energy harvesting.