Broadband directional control of thermal emission

Controlling the directionality of emitted far-field thermal radiation is a fundamental challenge. Photonic strategies enable angular selectivity of thermal emission over narrow bandwidths, but thermal radiation is a broadband phenomenon. The ability to constrain emitted thermal radiation to fixed narrow angular ranges over broad bandwidths is an important, but lacking, capability. We introduce gradient epsilon-near-zero (ENZ) materials that enable broad-spectrum directional control of thermal emission. We demonstrate two emitters consisting of multiple oxides that exhibit high (>0.7, >0.6) directional emissivity (60° to 75°, 70° to 85°) in the p-polarization for a range of wavelengths (10.0 to 14.3 micrometers, 7.7 to 11.5 micrometers). This broadband directional emission enables meaningful radiative heat transfer primarily in the high emissivity directions. Decoupling the conventional limitations on angular and spectral response improves performance for applications such as thermal camouflaging, solar heating, radiative cooling, and waste heat recovery.

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Experimental investigation of a radiative heat pipe for waste heat recovery in a ceramics kiln

Energy ◽

10.1016/j.energy.2018.12.133 ◽

2019 ◽

Vol 170 ◽

pp. 636-651 ◽

Cited By ~ 21

Author(s):

Bertrand Delpech ◽

Brian Axcell ◽

Hussam Jouhara

Keyword(s):

Experimental Investigation ◽

Heat Pipe ◽

Heat Recovery ◽

Waste Heat Recovery ◽

Radiative Heat ◽

Waste Heat

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Experimental Investigation of Thermoelectric Power Generation Using Radiative Heat Exchange

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.1025-1026.1125 ◽

2014 ◽

Vol 1025-1026 ◽

pp. 1125-1133

Author(s):

Niran Watcharodom ◽

Withaya Puangsombut ◽

Joseph Khedari ◽

Narong Vatcharasatien ◽

Jongjit Hirunlabh

Keyword(s):

Power Generation ◽

Experimental Investigation ◽

Heat Exchange ◽

Waste Heat Recovery ◽

Radiative Heat ◽

Waste Heat ◽

Electrical Power ◽

Air Gap ◽

Radiative Heat Exchange ◽

Thermoelectric Modules

This paper reports experimental investigation of a new concept of waste heat recovery for Thermoelectric Power Generation using Radiative heat exchange principle (TERX). To this end a small scale experimental setup was considered; it was composed of a heated plate, an absorber plate, thermoelectric modules and water cooled heat sink. The dimensions of absorber and heated plates were 0.2 m width and 0.3 m length. The air gap space between the two plates could be adjusted. Ten thermoelectric modules were connected in series parallel (5x2). Tests were made for different air gap spaces and fixed water flow rate (2L/min). A constant electric current (200W) was supplied to the heater of hot plate. Data collected included temperature at various positions and the electrical power generated. Experimental investigation confirmed that using radiative heat exchange principle could be considered for TE waste heat power generation. Increasing air gap decreased the electrical power generated as less radiative heat is absorbed by the thermoelectric modules. Under test conditions, the maximum measured electrical power is 0.3132 W at 0.5 cm of air gap, the corresponding temperature difference between the hot and cool sides of thermoelectric modules was about 35oC. Due to its simplicity of installation as no there is no need for direct contact between the thermoelectric generation set and the source of heat, the proposed concept offers a new alternative for waste heat recovery.

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Thermal Radiative Heat Transfer Between Closely Spaced Nanostructures

Design, Synthesis, and Applications ◽

10.1115/nano2005-87066 ◽

2005 ◽

Author(s):

L. Hu ◽

G. Chen

Keyword(s):

Heat Transfer ◽

Emission Spectrum ◽

Radiative Heat ◽

Thermal Emission ◽

Narrow Band ◽

Waste Heat ◽

Emission Control ◽

Photovoltaic Cell ◽

Potential Applications ◽

Thermal Emission Spectrum

Thermal emission control with nanostructures has attracted considerable attention because of its potential applications in thermophotovoltaic (TPV) devices [1–3]. The optical-to-electrical conversion in a TPV system is driven by photons with energy higher than the electronic bandgap of the photovoltaic cell. A narrow-band emitter with emission spectrum slightly above the bandgap is ideal, which maximizes the conversion efficiency as well as minimizes the waste heat that deteriorates the performance of the cell. Specially designed nanostructures alters the band structure of photons in much the same way as the crystal lattice does on electrons inside semiconductors, thus changing the thermal emission spectrum. By employing nanostructure-enabled emission control, Lin, et al, projected an efficiency of 34% for TPV systems [2].

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Spectral and Directional Control of Thermal Radiation With Periodic Structured Materials

ASME 2012 Third International Conference on Micro/Nanoscale Heat and Mass Transfer ◽

10.1115/mnhmt2012-75139 ◽

2012 ◽

Cited By ~ 1

Author(s):

Weijie Wang ◽

Ceji Fu ◽

Wenchang Tan

Keyword(s):

Photonic Crystals ◽

Thermal Radiation ◽

Thermal Emission ◽

Emission Angle ◽

Angular Frequency ◽

Radiative Properties ◽

Structured Materials ◽

Thermal Radiative Properties ◽

Directional Control ◽

Periodic Microstructures

Spectral and directional control of thermal emission holds substantial importance in different kinds of applications, where heat transfer is predominantly by thermal radiation. Several configurations have previously been proposed, like using gratings, photonic crystals, and resonant cavities. In the present work, we theoretically investigate the influence of periodic microstructures such as micro-scale gratings and photonic crystals on the thermal radiative properties of a structure constituted with these periodic microstructures. The enhanced thermal emission is found to be due to different excitation modes and the coupling between them. In order to offer insight into the mechanisms, we calculate and visualize the electromagnetic field profile at specified emission peaks. Furthermore, the emissivity pattern is calculated as a function of the emission angle and the angular frequency. The results reveal detailed spectral and directional dependence, and omnidirectional feature of thermal emission from the proposed structure. We show that it is possible to flexibly control the emission behavior by adjusting the structure dimensional parameters properly.

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Harvesting Nanoscale Thermal Radiation Using Pyroelectric Materials

Journal of Heat Transfer ◽

10.1115/1.4001634 ◽

2010 ◽

Vol 132 (9) ◽

Cited By ~ 36

Author(s):

Jin Fang ◽

Hugo Frederich ◽

Laurent Pilon

Keyword(s):

Heat Transfer ◽

Thermal Radiation ◽

Energy Conversion ◽

Power Output ◽

Radiative Heat ◽

Vinylidene Fluoride ◽

Waste Heat ◽

Heat Fluxes ◽

Working Fluid ◽

New Device

Pyroelectric energy conversion offers a way to convert waste heat directly into electricity. It makes use of the pyroelectric effect to create a flow of charge to or from the surface of a material as a result of heating or cooling. However, an existing pyroelectric energy converter can only operate at low frequencies due to a relatively small convective heat transfer rate between the pyroelectric materials and the working fluid. On the other hand, energy transfer by thermal radiation between two semi-infinite solids is nearly instantaneous and can be enhanced by several orders of magnitude from the conventional Stefan–Boltzmann law as the gap separating them becomes smaller than Wien’s displacement wavelength. This paper explores a novel way to harvest waste heat by combining pyroelectric energy conversion and nanoscale thermal radiation. A new device was investigated numerically by accurately modeling nanoscale radiative heat transfer between a pyroelectric element and hot and cold plates. Silica absorbing layers on top of every surface were used to further increase the net radiative heat fluxes. Temperature oscillations with time and performances of the pyroelectric converter were predicted at various frequencies. The device using 60/40 porous poly(vinylidene fluoride–trifluoroethylene) achieved a 0.2% efficiency and a 0.84 mW/cm2 electrical power output for the cold and hot sources at 273 K and 388 K, respectively. Better performances could be achieved with 0.9Pb(Mg1/3Nb2/3)–0.1PbTiO3 (0.9PMN-PT), namely, an efficiency of 1.3% and a power output of 6.5 mW/cm2 between the cold and hot sources at 283 K and 383 K, respectively. These results are compared with alternative technologies, and suggestions are made to further improve the device.

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