Illustration of nanopillars used in a new design to efficiently convert heat energy into electricity.
Researchers at the National Institute of Standards and Technology (NIST) have fabricated a novel device that could dramatically boost the conversion of heat into electricity. If perfected, the technology could help recoup some of the heat energy that is wasted in the U.S. at a rate of about $100 billion each year.
The new fabrication technique — developed by NIST researcher Kris Bertness and her collaborators — involves depositing hundreds of thousands of microscopic columns of gallium nitride atop a silicon wafer. Layers of silicon are then removed from the underside of the wafer until only a thin sheet of the material remains. The interaction between the pillars and the silicon sheet slows the transport of heat in the silicon, enabling more of the heat to convert to electric current. Bertness and her collaborators at the University of Colorado Boulder reported the findings online March 23 in Advanced Materials.
Once the fabrication method is perfected, the silicon sheets could be wrapped around steam or exhaust pipes to convert heat emissions into electricity that could power nearby devices or be delivered to a power grid. Another potential application would be cooling computer chips.
By growing nanopillars above a silicon membrane, NIST scientists and their colleagues have reduced heat conduction by 21% without reducing electrical conductivity, a result that could dramatically boost the conversion of heat energy into electrical energy. In solids, heat energy is carried by phonons, periodic vibrations of atoms in a crystal lattice. Certain vibrations of the phonons in the membrane resonate with those in the nanopillars, acting to slow the transfer of heat. Crucially, the nanopillars do not slow the movement of electrons, so that electrical conductivity remains high, creating a superior thermoelectric material. Credit: S. Kelley/NIST
The NIST-University of Colorado study is based on a curious phenomenon first discovered by German physicist Thomas Seebeck. In the early 1820s, Seebeck was studying two metal wires, each made of a different material, that were joined at both ends to form a loop. He observed that when the two junctions connecting the wires were kept at different temperatures, a nearby compass needle deflected. Other scientists soon realized that the deflection occurred because the temperature difference induced a voltage between the two regions, causing current to flow from the hotter region to the colder one. The current created a magnetic field that deflected the compass needle.
In theory, the so-called Seebeck effect could be an ideal way to recycle heat energy that would otherwise be lost. But there’s been a major obstacle. A material must conduct heat poorly in order to maintain a temperature difference between two regions yet conduct electricity extremely well to convert the heat to a substantial amount of electrical energy. For most substances, however, heat conductivity and electrical conductivity go hand in hand; a poor heat conductor makes for a poor electrical conductor and vice versa.
In studying the physics of thermoelectric conversion, theorist Mahmoud Hussein of the University of Colorado discovered that these properties could be decoupled in a thin membrane covered with nanopillars — standing columns of material no more than a few millionths of a meter in length, or about one-tenth the thickness of a human hair. His finding led to the collaboration with Bertness.
Using the nanopillars, Bertness, Hussein and their colleagues succeeded in uncoupling the heat conductivity from electrical conductivity in the silicon sheet — a first for any material and a milestone for enabling efficient conversion of heat to electrical energy. The researchers reduced the heat conductivity of the silicon sheet by 21% without lowering its electrical conductivity or changing the Seebeck effect.
In silicon and other solids, atoms are constrained by bonds and cannot move freely to transmit heat. As a consequence, the transport of heat energy takes the form of phonons — moving collective vibrations of the atoms. Both the gallium nitride nanopillars and the silicon sheet carry phonons, but those within the nanopillars are standing waves, pinned down by the walls of the tiny columns much the way a vibrating guitar string is held fixed at both ends.
The interaction between the phonons traveling in the silicon sheet and the vibrations in the nanopillars slow the traveling phonons, making it harder for heat to pass through the material. This reduces the thermal conductivity, thus increasing the temperature difference from one end to the other. Just as importantly, the phonon interaction accomplishes this feat while leaving the electrical conductivity of the silicon sheet unchanged.
The team is now working on structures fabricated entirely of silicon and with a better geometry for thermoelectric heat recovery. The researchers expect to demonstrate a heat-to-electricity conversion rate high enough to make their technique economically viable for industry.
Original Article: NIST Team Demonstrates Novel Way to Convert Heat to Electricity
The Latest Updates from Bing News
Go deeper with Bing News on:
Thermoelectric heat recovery
- Thermoelectric Generator (TEG) Market Sets New Record, Projected At USD 1443.3 Billion By 2030 At 11.8% CAGR: AMR
End-use Industry of thermoelectric generators includes automotive, aerospace, industrial, consumer and healthcare. The aerospace segment accounted for the largest share of the thermoelectric ...
- Thermoelectric Generator Converts Waste Heat into Energy
A miniature, thin-film thermoelectric generator (TEG) converts heat directly into electricity and is suited for waste-heat conversion applications. Developed by Nextreme, the TEG can be integrated ...
- Complex thermoelectric materials
Thermoelectric materials, which can generate electricity from waste heat or be used as solid-state Peltier coolers, could play an important role in a global sustainable energy solution.
- Heat Recovery Ventilation stock illustrations
Air handler with heating, cooling unit, recuperator and conditioner vector illustration. Technical image. heat recovery ventilation stock illustrations Air handler with heating, cooling unit, ...
- What are the challenges and benefits of implementing waste heat recovery systems in plant design?
selecting a waste heat recovery technology that is suitable for recovery, such as heat exchangers or thermoelectric generators. After that, optimizing the system by designing and sizing its ...
Go deeper with Bing News on:
Heat to electricity
- Dreading your winter heating bills? Here's how to save on gas, electricity
City Utilities suggested customers combine efficiency with a $75 rebate by purchasing an ENERGY STAR-rated smart thermostat ... setting them higher at 140 degrees can result not only in heat and ...
- Heat pumps vs. AC: Report notes progress, challenges in reaching climate goals
The IEA report found the momentum behind energy efficiency continued to increase in part due to the global energy crisis resulting from Russia's invasion of Ukraine.
- Google taps on geothermal heat to power its energy-hungry data centers
Traditional geothermal technologies can only be deployed economically in areas where underground heat is easily accessible. Enhanced geothermal power can tap into the potential of geothermal energy in ...
- Tips on how to save energy at home and help the planet
One of the most effective ways of cutting your home's emissions is by reducing heat loss through the insulation of walls, roofs and floors. In an uninsulated home, about a third of heat is lost ...
- Interest in solar energy continues to grow in Nova Scotia, non-profit group says
Recent discussion on home-heating efficiency has focused attention on heat pumps and green energy. Information Morning Cape Breton spoke to Dave Brushett with Solar NS to hear about what that's meant ...