>> Emerging Technologies that May Help Power the Future:-
¤ Next-gen Power Plants-
Researchers in Georgia Tech’s School of Mechanical Engineering are working on major makeovers for power plants, introducing innovations that range from revamped power cycles to new infrastructure materials.
In one project, steam is being replaced with supercritical carbon dioxide (SCCO2) as the working fluid to operate turbines and produce electricity.
SCCO2 results when carbon dioxide is subjected to pressure above 7.4 megapascals and temperatures above 31 degrees Celsius. This magical state, somewhere between a liquid and a gas, provides high fluid density, thermal conductivity, and heat capacity.
SCCO2 is currently used in environmentally friendly dry cleaning and coffee decaffeination. In energy applications, its high density and compressibility would enable generators to extract more power from turbines, explained Devesh Ranjan, an associate professor of fluid mechanics. “Equipment could be made from top-notch materials, yet dramatically smaller, which would reduce production costs.”
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Another plus: the unique cooling properties of SCCO2. “Most power plants are near a lake or river because they need lots of water to cool them,” Ranjan said. “Because the heat transfer coefficient is very high with SCCO2, you can do dry cooling in an arid environment such as the desert, which is best for solar collection.”
Using SCCO2 in concentrated solar plants could push thermal efficiencies from 45 to 60 percent, enough to be competitive with fossil fuel, said Asegun Henry, an assistant professor of heat transfer, combustion, and energy systems. “Yet this requires higher operating temperatures — 800 degrees Celsius compared to current temperatures below 600 degrees — and current heat exchangers literally can’t take the pressure.”
To resolve this, Henry and Ranjan are working with Purdue University researchers to develop a new breed of heat exchanger that can withstand extremely high temperatures and pressures, a project supported by DOE SunShot funding.
Ken Sandhage, a former Georgia Tech professor now at Purdue’s School of Material Engineering, has developed a process for inexpensively fabricating a high-temperature composite material into complicated 3-D shapes.
In addition to making solar power more competitive, the heat exchangers could also be used with SCCO2 to boost efficiency in fossil fuel power plants. “More efficiency means less carbon dioxide emissions per kilowatt produced,” Henry said.
¤ Monolithic Microscale Heat Pumps-
Proving that good things come in small packages, researchers led by Srinivas Garimella have developed a novel textbook-sized cooling system that operates on waste heat rather than electricity.
The underlying technology has been used in very large-scale installations, such as hospitals and university campuses, explained Garimella, a professor in Georgia Tech’s School of Mechanical Engineering.
Yet his team takes the science to a new level by working at the micro scale and creating a self-contained unit.
How it works: Extremely small passages are etched into thin sheets of metal with different areas representing different components. Working fluids flow in the same order as they would in a larger system, albeit in one space.
The minimization of plumbing inlets and outlets translates into greater compactness — and lower price tags.
Other advantages:
- No synthetic refrigerants are used, and less fluid is required, which further lowers costs and increases safety.
- No compressor is needed and there are few moving parts, decreasing noise and increasing reliability.
- Modular design allows units to be configured to generate anywhere from a few watts to tens of kilowatts of cooling or heating.
Since unveiling a proof-of-concept unit in 2009, the researchers have developed heat pumps with cooling capacities of one and two refrigerant tons. (Capacity of current residential units ranges from one to four refrigerant tons.)
Efficiency has been substantially improved, and fabrication techniques have also been improved to enable mass production.
Efficiency has been substantially improved, and fabrication techniques have also been improved to enable mass production.
Block diagram-Monolithic Absorption heat pump
“Although initial cost to consumers might be higher than traditional heat pumps, lifecycle costs should be comparable because of lower operating costs,”
Garimella said, noting that field tests are slated for late this year, and the technology might be ready for commercialization by 2017.
The researchers have also adapted the technology to provide cooling using waste heat from diesel-driven generators at military bases, where ambient temperatures are extremely high.
“Not only is diesel fuel very expensive to transport, there are also risks to humans in delivering the fuel,” Garimella said. “Using the energy in the diesel fuel to the fullest extent by providing power as well as cooling through these units, without consuming additional prime energy, will lower overall costs and increase personnel safety.”
The research has been supported by ARPA-E, Department of Energy, U.S. Army, Naval Facilities Engineering Command, Georgia Research Alliance, and Atlanta Gas Light.
¤ Recycling Radio Waves-
Researchers led by Manos Tentzeris have developed an electromagnetic energy harvester that can collect enough ambient energy from the radio frequency (RF) spectrum to operate devices for the Internet of Things (IoT), smart skin and smart city sensors, and wearable electronics.
Harvesting radio waves is not brand new, but previous efforts have been limited to short-range systems located within meters of the energy source, explained Tentzeris, a professor in Georgia Tech’s School of Electrical and Computer Engineering.
His team is the first to demonstrate long-range energy harvesting as far as seven miles from a source.
Pic-Recycles airborne radio Waves
The researchers unveiled their technology in 2012, harvesting tens of microwatts from a single UHF television channel.
Since then, they’ve dramatically increased capabilities to collect energy from multiple TV channels, Wi-Fi, cellular, and handheld electronic devices, enabling the system to harvest power in the order of milliwatts. Hallmarks of the technology include:
- Ultra-wideband antennas that can receive a variety of signals in different frequency ranges.
- Unique charge pumps that optimize charging for arbitrary loads and ambient RF power levels.
- Antennas and circuitry, 3-D inkjet-printed on paper, plastic, fabric, or organic materials, that are flexible enough to wrap around any surface. (The technology uses principles from origami paper-folding to create “smart” shape-changing complex structures that reconfigure themselves in response to incoming electromagnetic signals.)
The researchers have recently adapted the harvester to work with other energy-harvesting devices, creating an intelligent system that probes the environment and chooses the best source of ambient energy to collect. What’s more, it combines different forms of energy, such as kinetic and solar, or electromagnetic and vibration.
Although some work remains to scale the printing process, commercialization of the National Science Foundation-supported research could happen within two years.
¤ Flexible Generators-
Yee’s group is also pioneering the use of polymers in thermoelectric generators (TEGs).
Solid-state devices that directly convert heat to electricity without moving parts, TEGs are typically made from inorganic semiconductors.
Yet polymers are attractive materials due to their flexibility and low thermal conductivity. These qualities enable clever designs for high-performance devices that can operate without active cooling, which would dramatically reduce production costs.
The researchers have developed P- and N-type semiconducting polymers with high performing ZT values (an efficiency metric for thermoelectric materials). “We’d like to get to ZT values of 0.5, and we’re currently around 0.1, so we’re not far off,” Yee said.
Pic- Flexible thermoelectirc Generator module
Pic- Flexible generator harness energy from movement
In one project funded by the Air Force Office of Scientific Research, the team has developed a radial TEG that can be wrapped around any hot water pipe to generate electricity from waste heat.
Such generators could be used to power light sources or wireless sensor networks that monitor environmental or physical conditions, including temperature and air quality.
“Thermoelectrics are still limited to niche applications, but they could displace batteries in some situations,” Yee said. “And the great thing about polymers, we can literally paint or spray material that will generate electricity.”
This opens opportunities in wearable devices, including clothing or jewelry that could act as a personal thermostat and send a hot or cold pulse to your body.
Granted, this can be done now with inorganic thermoelectrics, but this technology results in bulky ceramic shapes, Yee said. “Plastics and polymers would enable more comfortable, stylish options.”
Although not suitable for grid-scale application, such devices could provide significant savings, he added.
Granted, this can be done now with inorganic thermoelectrics, but this technology results in bulky ceramic shapes, Yee said. “Plastics and polymers would enable more comfortable, stylish options.”
Although not suitable for grid-scale application, such devices could provide significant savings, he added.
¤ New Breed of Betavoltaics-
In another project, Yee’s group is using nuclear waste to produce electricity — minus the reactor and sans moving parts.
Funded by the Defense Advanced Research Projects Agency (DARPA) and working in collaboration with Stanford University, the researchers have developed a technology that is similar to photovoltaic devices with one big exception: Instead of using photons from the sun, it uses high-energy electrons emitted from nuclear byproducts.
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Betavoltaic technology has been around since the 1950s, but researchers have focused on tritium or nickel-63 as beta emitters. “Our idea was to revisit the technology from a radiation transport perspective and use strontium-90, a prevalent isotope in nuclear waste,” Yee said.
Strontium-90 is unique because it emits two high-energy electrons during its decay process. What’s more, strontium-90’s energy spectrum aligns well with design architecture already used in crystalline silicon solar cells, so it could yield highly efficient conversion devices.
In lab-scale tests with electron beam sources, the researchers have been achieving power conversion efficiencies of between 4 and 18 percent.
With continued improvements, Yee believes the betavoltaic devices could ultimately generate about one watt of power continuously for 30 years — which would be 40,000 times more energy dense than current lithium ion batteries.
Initial applications include military equipment that requires low-power energy for long periods of time or powering devices in remote locations where changing batteries is problematic.
With continued improvements, Yee believes the betavoltaic devices could ultimately generate about one watt of power continuously for 30 years — which would be 40,000 times more energy dense than current lithium ion batteries.
Initial applications include military equipment that requires low-power energy for long periods of time or powering devices in remote locations where changing batteries is problematic.
