An international research team has used a “thermal metamaterial” to control the emission of radiation at high temperatures, an advance that could bring devices able to efficiently harvest waste heat from power plants and factories.
Roughly 50 to 60 percent of the energy generated in coal and oil-based power plants is wasted as heat. However, thermophotovoltaic devices that generate electricity from thermal radiation might be adapted to industrial pipes in factories and power plants, as well as on car engines and automotive exhaust systems, to recapture much of the wasted energy.
In new findings, researchers demonstrated how to restrict emission of thermal radiation to a portion of the spectrum most needed for thermophotovoltaic technology.
“These devices require spectrally tailored thermal emission at high temperatures, and our research shows that intrinsic material properties can be controlled so that a very hot object glows only in certain colors,” said Zubin Jacob, an assistant professor of electrical and computer engineering at Purdue University. “The main idea is to start controlling thermal emission at record high temperatures in ways that haven’t been done before.”
The thermal metamaterial – nanoscale layers of tungsten and hafnium oxide – was used to suppress the emission of one portion of the spectrum while enhancing emission in another. (An animation is available at https://youtu.be/dbePERsPh-g)
Metamaterials are composite media that contain features, patterns or elements such as tiny nanoantennas that enable an unprecedented control of light. Under development for about 15 years, the metamaterials owe their unusual abilities to precision design and manufacture on the scale of nanometers.
“They have been used mainly to manipulate coherent light, as in a laser, but the ability to manipulate infrared thermal radiation at 1,000 C opens up new areas of research,” Jacob said. “The technique we used to achieve this thermal suppression and enhancement is fundamentally different from existing thermal engineering approaches and harnesses a phenomenon called topological transitions.”
Findings were detailed in a research paper published earlier this year in the journal Nature Communications. The work was performed by researchers at Purdue, the Hamburg University of Technology in Germany; University of Alberta in Canada; and Helmholtz-Zentrum Geesthacht Centre for Materials and Coastal Research in Germany. The co-lead authors were Hamburg University of Technology postdoctoral researcher Pavel Dyachenko and University of Alberta doctoral student Sean Molesky.
The research represents the first time the approach was used for thermal emission in high-temperature metamaterials, also called refractory metamaterials.
“My student, Sean Molesky, theoretically predicted it in 2012, and it has taken about four years and some exceptional materials engineering from our collaborators to perform the high-temperature experiments and demonstrate the thermal metamaterial,” Jacob said.
The basic operating principle of a photovoltaic cell is that a semiconducting material is illuminated with light, causing electrons to move from one energy level to another. Electrons in the semiconductor occupy a region of energy called the valence band while the material is in the dark. But shining light on the material causes the electrons to absorb energy, elevating them into a region of higher energy called the conduction band. As the electrons move to the conduction band, they leave behind “holes” in the valance band. The region between both bands, where no electrons exist, is called the band gap.
“If you have energy below the band gap, that is generally wasted,” Jacob said. “So what you want to do for high-efficiency thermal energy conversion is suppress the thermal emission below the band gap and enhance it above the band gap, and this is what we have done. We have used the topological transition in a way that was not done before for thermal enhancement and suppression, enhancing the high-energy part of the emission spectrum and suppressing the low-energy thermal photons. This allows us to emit light only within the energy spectrum above the band gap.”
The paper’s other authors were Jacob; Hamburg University of Technology researchers Alexander Yu Petrov, Slawa Lang, Manfred Eich, T. Krekeler and M. Ritter; and senior research scientist Michael Störmer from the Helmholtz-Zentrum Geesthacht Centre for Materials and Coastal Research.
Future research will include work to convert heat radiation from a thermal metamaterial to electron-hole pairs in a semiconducting material, a critical step in developing the technology. The thermophotovoltaic technology might be ready for commercialization within seven years, Jacob said.
A graphic depicting the high-temperature thermal metamaterial is available athttps://news.uns.purdue.edu/images/2016/jacob-topological.jpg
The graphic depicts how the thermal radiation is controlled using the shape of the surfaces: the metamaterial enhances thermal radiation in the “ellipsoidal regime” at left, but suppresses it in the “hyperboloidal regime” at right.
The Latest on: Thermal metamaterial
via Google News
The Latest on: Thermal metamaterial
- 3D-Printed Metamaterial Shrinks Under High Heaton April 8, 2021 at 5:00 pm
Although it is made of two thermally expanding materials, star-shaped unit cells of the metamaterial have a mechanical design that promotes negative thermal expansion (NTE) when heat is applied.
- Heat conduction tuning by wave nature of phononson April 4, 2021 at 5:01 pm
We show a possibility to use the wave nature of heat for thermal conductivity tuning via spatial short-range order in phononic crystal nanostructures. Our experimental and theoretical results suggest ...
- Temperature-responsive biometamaterials for gastrointestinal applicationson April 4, 2021 at 5:01 pm
For the extra-esophageal compartment, we developed a highly flexible macrostructure (mechanical metamaterial) that deforms into a ... a large animal model that define anatomical, temporal, and thermal ...
- An insight into the estimation of frost thermal conductivity on parallel surface channels using kernel based GPR strategyon March 30, 2021 at 2:15 am
Thus, the study on the frost thermal conductivity has a significant and vital place for the engineers and researchers dealing with the heat exchangers. In the literature, there is a lack of ...
- Graphene Descriptionon August 14, 2020 at 7:56 pm
Thermal interface materials (TIMs ... The concept of plasmonic cloaking is based on the use of a thin metamaterial cover to suppress the scattering from a passive object. Research shows that even a ...
- Extended projects 2018 cohorton June 1, 2020 at 5:21 am
Moreover, hydrogels inserted in the fractal cavities were used to create a composite metamaterial structure to further improve ... A component made from thermoplastics can be repaired in service using ...
- Emerging Theories and Technologies in Metamaterialson July 5, 2019 at 8:03 pm
Elements cover the theory, characterisation, design and fabrication of metamaterials in areas such as electromagnetics and optics, plasmonics, acoustics and thermal science ... which extend the ...
- Manufacturing Bits: April 8on April 8, 2019 at 12:11 am
We could say: ‘Here is the behavior I want. Now tell me what the metamaterial looks like. ’” With metamaterials, researchers have developed an ultra-narrowband wavelength-selective thermal emitter.
- Beyond Invisibility: Engineering Light With Metamaterialson March 26, 2016 at 12:09 pm
An early metamaterial using repeating elements of ... A group in Germany has successfully created a thermal cloak, preventing an area from heating by bending the heat flow around it – just ...
via Bing News