
Research
The objective of this project is to provide a framework for performing largescale computation of nearfield thermal radiation in threedimensional (3D) complex geometries. Specifically, we proposed and implemented a novel method called the thermal discrete dipole approximation (TDDA) for simulating nearfield radiative heat transfer between 3D arbitrarilyshaped objects. The TDDA is inspired by the discrete dipole approximation (DDA), sometimes referred to as the Coupled Dipole Method (CDM), extensively used for predicting electromagnetic scattering and absorption by particles. In the TDDA, objects are discretized into cubical subvolumes behaving as electric point dipoles. The fluctuating electric dipoles are related to the local temperature of the emitter via the fluctuationdissipation theorem. The figure below shows a 500nm sphere discretized into 552 subvolumes (left panel). The thermal conductance obtained with the TDDA is compared against the exact results for two 500nm silica spheres separated by a 500nmthick gap (right panel).
A simulation of nearfield radiative heat transfer between two 8um spheres separated a vacuum gap having a thickness of 100 nm is shown below. The refractive index of both spheres is 3+0.01i, and the color scale shows the normalized volumetric power absorbed.
S. Edalatpour, M. Cuma, T. Trueax, R. Backman, and M. Francoeur, "Convergence analysis of the thermal discrete dipole approximation," Physical Review E, under review/in revision, 2015 (arXiv). S. Edalatpour and M. Francoeur, "The Thermal Discrete Dipole Approximation (TDDA) for nearfield radiative heat transfer simulations in threedimensional arbitrary geometries," Journal of Quantitative Spectroscopy and Radiative Transfer 133, 364373, 2014 (pdf). This work is sponsored by the Army Research Office (Grant No. W911NF1410210, 20142017). We also acknowledge the computational resources provided by the Center for High Performance Computing (CHPC) at the University of Utah.
NanoscaleGap Thermophotovoltaic Power Generation The objective of this project is to demonstrate experimentally that power generation in a nanoscalegap thermophotovoltaic (nanoTPV) device can be enhanced by an order of magnitude, compared to conventional TPV systems, due to radiation heat transfer exceeding the blackbody limit. We are currently in the process of measuring nearfield radiative heat transfer between two millimetersize silicon surfaces separated by vacuum gap thicknesses ranging from 2 um down to 100 nm. The experiments are performed within a vacuum chamber, in order to avoid parasitic heat conduction, that is located under a clean room tent.
We are also interested in quantifying the impacts of radiative, electrical and thermal losses on the performances of nanoTPV power generators. In the figure shown below, the power enhancement of nanoTPV devices with a tungsten and a radiativelyoptimized quasimonochromatic (Drude) radiator is compared. The results suggest that the design of optimal nanoTPV devices must account for all loss mechanisms, radiative, electrical and thermal.
M.P. Bernardi, O. Dupré, E. Blandre, P.O. Chapuis, R. Vaillon, and M. Francoeur, "Impacts of propagating, frustrated and surface modes on radiative, electrical and thermal losses in nanoscalegap thermophotovoltaic power generators," Scientific Reports, under review, 2015 (arXiv). M. Francoeur, "Chapter 4: Thermal Fundamentals," In: Micro Energy Harvesting, Edited by D. Briand, E. Yeatman and S. Roundy, WileyVCH, 2015 (link). M. Francoeur, R. Vaillon, and M.P. Mengüç, "Thermal impacts on the performance of nanoscalegap thermophotovoltaic energy conversion devices," IEEE Transactions on Energy Conversion, 26(2), 686698, 2011 (pdf). This work is sponsored by the National Science Foundation (Grant No. CBET1253577, 20132018).
Thermal Radiative Property Control via Metamaterials and Nanostructures
Evanescent Wave Scattering by Particles
