Over 2.5 billion people do not have access to safe and effective sanitation. Without a sanitary sewer infrastructure, self-contained modular systems can provide solutions for these people in the developing world and remote areas. Our team is building a better toilet that processes human waste into burnable fuel and disinfects the liquid waste. The toilet employs energy harvesting to produce electricity and does not require external electrical power or consumable materials. RTI has partnered with Colorado State University, Duke University, and Roca Sanitario under a Bill and Melinda Gates Foundation Reinvent the Toilet Challenge (RTTC) grant to develop an advanced stand-alone, self-sufficient toilet to effectively process solid and liquid waste. The system operates through the following steps: 1) Solid-liquid separation, 2) Solid waste drying and sizing, 3) Solid waste combustion, and 4) Liquid waste disinfection. Thermoelectric energy harvesting is a key component to the system and provides the electric power for autonomous operation. A portion of the exhaust heat is captured through finned heat-sinks and converted to electricity by thermoelectric (TE) devices to provide power for the electrochemical treatment of the liquid waste, pumps, blowers, combustion ignition, and controls.
Recent development efforts on thermoelectric (TE) power converters comprised of low-to-mid-temperature (25-400°C),
and high-temperature (400-750°C) materials have achieved >60 Watts electrical power with a thermal-to-electric
conversion efficiency of ~8%. This paper will focus on thermoelectric devices fabricated from these materials, and also
on cascaded power converters that enable the high power and efficiency to be obtained. In addition, work is underway
to explore the use of more advanced low- to mid-temperature TE materials that have achieved over 10% efficiency in a
single junction converter.
KEYWORDS: Thermoelectric materials, Prototyping, Computer aided design, Resistance, Fluctuations and noise, Gas lasers, Sensors, Energy harvesting, Temperature metrology, Energy efficiency
The addition of advanced sensors, targeting systems and electronic countermeasures to military vehicles has created a
strategic need for additional electric power. By incorporating a thermoelectric (TE) waste heat recovery system to
convert available exhaust heat to electricity, increased electric power needs can be met without reducing the energy
efficiency of the vehicle. This approach allows existing vehicles to be upgraded without requiring a complete re-design
of the engine and powertrain to support the integration of advanced electronic sensors and systems that keep the
performance at the state of the art level.
RTI has partnered with General Dynamics Land Systems and Creare, Inc. under an Army Research Lab program to
develop a thermoelectric exhaust waste heat recovery system for the M1 Abrams tank. We have designed a reduced-scale
system that was retrofitted to the tank and generated 80W of electric power on the vehicle operating on a test track
by capturing a portion of the exhaust heat from the Honeywell/Lycoming AGT-1500 gas turbine engine.
KEYWORDS: Thin film devices, Superlattices, Thermoelectric materials, Energy harvesting, Thin films, Stereolithography, Heat flux, Current controlled current source, Electronics, Bismuth
Thin film superlattice (SL) based thermoelectric (TE) devices offer the potential for improved efficiency and high heat flux cooling over conventional bulk materials. We have demonstrated external cooling of 55K and heat pumping capacity of 128 W/cm2 in single couples and temperature differences as high as 102K in three stage cascade structures. The high heat flux pumping capacity of these in thin film devices are also attractive for hot-spot cooling in electronics. These same materials have also been successfully employed in power generation and energy harvesting applications. In this presentation, we will discuss recent RTI advances in Bi2Te3-based thin-film SL (TFSL) devices for cooling and energy harvesting applications.
There is increasing need for self-sufficient power sources for wireless sensors and electronics that can extend device
performance beyond what is available from conventional batteries. Thermoelectric approaches for developing such
power sources using geothermal and body heat are attractive. RTI has developed a prototype "thermal ground stake"
wireless sensor node powered by thermoelectric (TE) energy harvesting that lends itself to unattended ground sensors for
covert military and intelligence operations where TE powered sensors are concealed in the ground. In another
application, RTI International and QUASAR are jointly developing an integrated body-worn biosensor system powered
by body heat thermoelectric energy harvesting.
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