Abstract
Thermal radiation plays an important role in many energy conversion processes. The capability to tailor thermal radiation using nanomaterials and photonic structures can represent important opportunities for energy and information applications. In this seminar I will talk about my recent studies on controlling thermal radiation for energy harvesting, active refrigeration, and thermal supercurrents.
First, I will discuss experiments on energy conversion based on nanoscale radiative heat transfer [1-2], which point to new opportunities for thermal energy harvesting. Specifically, I will describe an experiment on nanogap near-field thermophotovoltaics [2], where I demonstrated that the power generation rate can be greatly enhanced (40-fold) by reducing the distance between a hot thermal emitter and a photovoltaic cell to the nanoscale.
Second, I will discuss my recent studies on radiative heat transfer that illustrate how conventional constraints on radiative heat transfer where the direction of heat flow is set by the relative temperature difference can be overcome [1, 3]. In particular, I will describe a first experimental demonstration of active photonic refrigeration using incoherent light – thermal radiation, through control of the chemical potential of photons [1]. I will illustrate how net cooling on a surface can be obtained, by placing it in close proximity of a reverse-biased light emitting diode. The cooling arises due to a combination of suppressed thermal radiation from the reverse-biased diode, and enhanced photon emission from the surface across nanoscale gaps. This points to a promising way for solid state refrigeration by combining nanophotonics and optoelectronic devices.
Third, I will introduce a theoretical discovery of thermal supercurrents that exist even without any temperature bias [3]. I will discuss in detail how my investigations reveal that such persistent radiative heat currents can be accomplished in many-body non-reciprocal systems. This work points to a new regime of heat transfer – one that does not involve entropy generation. Finally, I will give an overview of my future research directions.
About the Speaker
Dr. Linxiao Zhu received his Ph.D. in applied physics and M.S. in electrical engineering, both from Stanford University, and a B.S. degree in physics from the University of Science and Technology of China. His doctoral research is on controlling electromagnetic heat transfer using photonic structures, supervised by Prof. Shanhui Fan. Dr. Zhu is currently a postdoctoral research fellow with Prof. Pramod Reddy and Prof. Edgar Meyhofer in Department of Mechanical Engineering at the University of Michigan, working on the experiments of near-field based energy conversion and refrigeration. Dr. Zhu is interested in controlling light and heat for energy and information applications. Dr. Zhu has been honored in MIT Technology Review 35 Innovators Under 35 (China region). His research has received media coverage such as in Discover, Scientific American etc.
