Friday, November 27, 2009

URI Nanocomposite Cermet Thermocouple Provides Heat Protection and Wireless Sensor Power in Aviation Applications

University of Rhode Island Professor of Chemical Engineering Otto J. Gregory; (Wakefield, RI), Gustave C. Fralick and John D. Wrbanek have created a nano-composite material with a high electrical conductivity and a high Seebeck coefficient and low thermal conductivity. The nano-composite material is capable of withstanding high temperatures and harsh conditions. These properties make it suitable for use as both a thermal barrier coating for turbine blades and vanes and a thermoelectric generator to power high temperature electronics, high temperature wireless transmitters, and high temperature sensors. Unique to these applications is that the thermal barrier coatings can act as a temperature sensor and/or a source of power for other sensors or high temperature electronics and wireless transmitters, according to U.S. Patent Application 20090290614.

They developed a nanocomposite cermet thermocouple material having a high voltage output and ultra low thermal conductivity, and is stable in hot oxidizing atmospheres, that allow it to be used as both thermoelectric generator and thermal barrier coating in the hot section of a turbine engine.

The Rhode Island nanocomposite cermet thermocouple replaces the presently used thermal barrier coating material (Yttria stabilized Zirconia) with nano-composite ceramic material on one side of the blade and indium-tin oxide on the other Convective heat transfer from the hot combustion gas to the blade and conductive heat transfer from the outer blade surface to the blade root creates a temperature gradient from the tip of the blade to the root that can be as large as C. Improved thermoelectric materials exploit this temperature difference to produce useable electric power

In a recent Department of Energy/Oak Ridge National Laboratory report, the needs for sensors and controls for advance turbine systems were assessed and the highest priority need identified was the accurate measurement of combustion gas temperature and flame detection up to C. to enable closed loop control of emissions. Also identified in this report was the need for the development of durable sensors to control combustion instabilities caused by lean fuel mixtures.

In order to meet the long-term instrumentation needs associated with NASA's Aircraft Aging and Durability (AAD) Project and its associated set of challenge problems (CP-07) related to Durability in Engine Hot Section (AAD-1), semi-conductive oxides and cermets (nanocomposites) will be used as the active sensor elements in temperature, strain and heat flux sensors. Indium tin oxide (ITO) thin films will serve as the sensor platform. ITO films were combined with nanocermets, to produce thin film thermocouples with very large thermoelectric powers. The large thermoelectric responses anticipated will be exploited in thermocouples, heat flux sensors and energy harvesting devices to power active wireless strain gages.

Ultimately, the implementation of the thin film sensors will be placed into the turbine section of gas turbine engines. These sensors will lead to improved reliability and extended performance. For example, the monitoring of temperature distribution and pattern factor in the combustion chamber of a gas turbine engine is critical since the lack of proper fuel burning can severely damage engine components and affect overall performance. The sensors advance the knowledge in the fundamental disciplines of aeronautics and are used to develop technologies for safer aircraft and higher capacity airspace systems. Specifically, advanced thin film instrumentation and associated fabrication methodologies will be developed for improving overall safety of new vehicles operating in the next generation air transportation system.

As the number of sensors is increased on modern gas turbine engines, it is increasingly desirable that the data be transmitted wirelessly. However, the sensors that provide the data and the radios that transmit the data need a source of power. Batteries are impractical because they are difficult to replace and cannot operate at high temperatures, so a local power source is necessary. At the same time, it is desirable to protect engine hot section blades and vanes from the hot combustion gases through use of low thermal conductivity ceramic coatings. The objective of this invention is to provide this thermal protection while at the same time providing power for wireless sensors and high temperature electronics.

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