Figure 8: The inside and outside of the EHTEG.
Converting to usable electricity
The thermal environment of each thermoelectric module was slightly different because of its location on the EHTEG, so each module’s output was also different from its neighbors. The input interface modules received the output from a pair of modules and converted the input voltage to 12 V. The input module also automatically adjusted its input impedance to match the source impedance, thus operating at the maximum power transfer point.
The outputs of the input modules were combined and fed to a single 12-V bus regulator that provided a regulated 12-V output to external loads. An electronic load was included in the power conditioning electronics for testing purposes. The electronic load automatically adjusts its resistance to extract the maximum power available from the EHTEG system. The data I/O board provided voltage levels proportional to selected voltage and current levels for input to the onboard data-logging system. For example, the total power delivered by EHTEG system could be computed by monitoring the output voltage and current flowing into the electronic regulator.
The engineer team used FloTHERM to create virtual models of the exhaust system, analyzing various design configurations quickly before building any physical prototypes. And the results of the CFD models correlated well with those obtained on the engineering test bed.
Because the TEGs are actually thermoelectric coolers run in reverse, their efficiency is only around 5 percent; that is, 5 percent of the heat energy flowing through is turned into electricity. If this efficiency rate can be doubled, the technology could be used in many practical and profitable applications. New commercial opportunities are spurring interest in thermoelectric power generation. The design techniques described here could be used to develop much higher power output thermal energy harvesting power systems.
Credit: Ambient Micro
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2. J. Langley, M. Taylor, G. Wagner, and S. Morris, “Thermoelectric Energy Harvesting from Small Aircraft Engines,” SAE International, 2009.
3. Marco Nuti, Emissions from Two-Stroke Engines, Society of Automotive Engineers, Inc., Chapters 7 and 9.
4. Combustion Products Applet:
Allan T. Kirkpatrick, Colorado State University, Fort Collins.
About the authors
has more than 39 years of experience in the electronics industry. His experience includes: IC and system cooling and packaging technology, disk drive design, computer system design, and design of telephone switching systems. Wagner, an expert in cooling of electronics systems and high-power ICs, has authored 17 papers at international conferences on this subject and has 26 patents. He has been doing thermal consulting since 2001. Before joining Electronic Cooling Solutions, he held positions as a Director of Engineering at Cornice Inc.; member of technical staff at Storage Genetics; Chief Scientist for the HP/Agilent Technologies PolarLogic business unit; and member of technical staff at AT&T Bell Laboratories. Wagner has a Master of Science degree in Mechanical Engineering from Iowa State University.
has a Master of Science degree in Aerospace Engineering from Carleton University, with a research focus on rotorcraft aerodynamics and aeroelasticity. Mikjaniec has spent the past five years working for Mentor Graphics Corporation, Mechanical Analysis Division (formerly Flomerics Ltd.), specializing in the application of CFD to the design of electronics equipment.
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