12 research outputs found
Enhancement and tunability of near-field radiative heat transfer mediated by surface plasmon polaritons in thin plasmonic films
The properties of thermal radiation exchange between hot and cold objects can
be strongly modified if they interact in the near field where electromagnetic
coupling occurs across gaps narrower than the dominant wavelength of thermal
radiation. Using a rigorous fluctuational electrodynamics approach, we predict
that ultra-thin films of plasmonic materials can be used to dramatically
enhance near-field heat transfer. The total spectrally integrated film-to-film
heat transfer is over an order of magnitude larger than between the same
materials in bulk form and also exceeds the levels achievable with polar
dielectrics such as SiC. We attribute this enhancement to the significant
spectral broadening of radiative heat transfer due to coupling between surface
plasmon polaritons (SPPs) on both sides of each thin film. We show that the
radiative heat flux spectrum can be further shaped by the choice of the
substrate onto which the thin film is deposited. In particular, substrates
supporting surface phonon polaritons (SPhP) strongly modify the heat flux
spectrum owing to the interactions between SPPs on thin films and SPhPs of the
substrate. The use of thin film phase change materials on polar dielectric
substrates allows for dynamic switching of the heat flux spectrum between
SPP-mediated and SPhP-mediated peaks.Comment: 25 pages, 11 figure
Heat meets light on the nanoscale
We discuss the state-of-the-art and remaining challenges in the fundamental
understanding and technology development for controlling light-matter
interactions in nanophotonic environments in and away from thermal equilibrium.
The topics covered range from the basics of the thermodynamics of light
emission and absorption, to applications in solar-thermal energy generation,
thermophotovoltaics, optical refrigeration, personalized cooling technologies,
development of coherent incandescent light sources, and spinoptics.Comment: 46 pages, 11 figures; to appear in the special issue of Nanophotonics
on 'Smart nanophotonics for renewable energy and sustainability' 201
Heat meets light on the nanoscale
We discuss the state-of-the-art and remaining challenges in the fundamental understanding and technology development for controlling light-matter interactions in nanophotonic environments in and away from thermal equilibrium. The topics covered range from the basics of the thermodynamics of light emission and absorption to applications in solar thermal energy generation, thermophotovoltaics, optical refrigeration, personalized cooling technologies, development of coherent incandescent light sources, and spinoptics
Diverging polygon-based modeling (DPBM) of concentrated solar flux distributions
This paper presents an efficient and robust methodology for modeling concentrated solar flux distributions. Compared to ray tracing methods, which provide high accuracy but can be computationally intensive, this approach makes a number of simplifying assumptions in order to reduce complexity by modeling incident and reflected flux as a series of simple geometric diverging polygons, then applying shading and blocking effects. A reduction in processing time (as compared to ray tracing) allows for evaluating and visualizing numerous combinations of engineering and operational variables (easily exceeding 106 unique iterations) to ascertain instantaneous, transient, and annual system performance. The method is demonstrated on a linear Fresnel reflector array and a number of variable iteration examples presented. While some precision is sacrificed for computational speed, flux distributions were compared to ray tracing (SolTrace) and average concentration ratio generally found to agree within ∼3%. This method presents a quick and very flexible coarse adjust method for concentrated solar power (CSP) field design, and can be used to both rapidly gain an understanding of system performance as well as to narrow variable constraint windows for follow-on high accuracy system optimization.United States. Defense Advanced Research Projects Agency (Award DE-AR0000471
Diverging polygon-based modeling (DPBM) of concentrated solar flux distributions
This paper presents an efficient and robust methodology for modeling concentrated solar flux distributions. Compared to ray tracing methods, which provide high accuracy but can be computationally intensive, this approach makes a number of simplifying assumptions in order to reduce complexity by modeling incident and reflected flux as a series of simple geometric diverging polygons, then applying shading and blocking effects. A reduction in processing time (as compared to ray tracing) allows for evaluating and visualizing numerous combinations of engineering and operational variables (easily exceeding 106 unique iterations) to ascertain instantaneous, transient, and annual system performance. The method is demonstrated on a linear Fresnel reflector array and a number of variable iteration examples presented. While some precision is sacrificed for computational speed, flux distributions were compared to ray tracing (SolTrace) and average concentration ratio generally found to agree within ∼3%. This method presents a quick and very flexible coarse adjust method for concentrated solar power (CSP) field design, and can be used to both rapidly gain an understanding of system performance as well as to narrow variable constraint windows for follow-on high accuracy system optimization.United States. Defense Advanced Research Projects Agency (Award DE-AR0000471
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Giant heat transfer in the crossover regime between conduction and radiation
Heat is transferred by radiation between two well-separated bodies at temperatures of finite difference in vacuum. At large distances the heat transfer can be described by black body radiation, at shorter distances evanescent modes start to contribute, and at separations comparable to inter-atomic spacing the transition to heat conduction should take place. We report on quantitative measurements of the near-field mediated heat flux between a gold coated near-field scanning thermal microscope tip and a planar gold sample at nanometre distances of 0.2–7 nm. We find an extraordinary large heat flux which is more than five orders of magnitude larger than black body radiation and four orders of magnitude larger than the values predicted by conventional theory of fluctuational electrodynamics. Different theories of phonon tunnelling are not able to describe the observations in a satisfactory way. The findings demand modified or even new models of heat transfer across vacuum gaps at nanometre distances