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Research Papers: Heat Energy Generation/Storage/Transfer

# Design to Maximize Performance of a Thermoelectric Power Generator With a Dynamic Thermal Power Source

[+] Author and Article Information
Douglas T. Crane

BSST LLC, 5462 Irwindale Avenue, Irwindale, CA 91706dcrane@bsst.com

Lon E. Bell

BSST LLC, 5462 Irwindale Avenue, Irwindale, CA 91706

J. Energy Resour. Technol 131(1), 012401 (Feb 05, 2009) (8 pages) doi:10.1115/1.3066392 History: Received December 06, 2007; Revised September 23, 2008; Published February 05, 2009

## Abstract

It is a difficult technical challenge to design thermoelectric power generation systems that work optimally over a broad dynamic range of thermal input power. Conventional systems are designed to work optimally for a nominal operating condition, while maintaining the ability to operate at off nominal and extreme operating conditions without damage to the system. For systems that operate in a narrow range of thermal power conditions, thermoelectric waste heat recovery system design is simplified. However, for applications that do have a wide range of operating conditions, designs typically exhibit overall average efficiencies that are reduced by approximately 20% or more compared with that achievable for the thermoelectric material operating at peak efficiency. Both cars and trucks consume significant fuel at low mass flow rates. Since the ultimate goal of waste heat recovery systems is to minimize fuel consumption, it is critical that the recovery system be designed to operate near peak efficiency over the range of mass flow rates that make a significant contribution to overall power recovery. Such performance capability is especially important in city driving, and in hybrid vehicle applications. This paper describes a design concept that maximizes the performance for thermoelectric power generation systems in which the thermal power to be recovered is from a fluid stream (e.g., exhaust gas) subject to varying temperatures and a broad range of exhaust flow rates. The device is constructed in several parts, with each part optimized for a specific range of operating conditions. The thermoelectric system characteristics, inlet mass flow rates and fluid temperatures, and load and internal electrical resistances are monitored and generator operation is controlled to maximize performance. With this design, the system operates near optimal efficiency for a much wider range of operating conditions. Application of the design concept to an automobile is used to show the benefits to overall system performance.

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## Figures

Figure 1

Figure of merit (ZT) for current TE material (p-type and n-type) over the temperature range of 0–1000°C(13)

Figure 2

Example of TE impedance mismatch. TE hot side temperature=500 K; TE cold side temperature=300 K.

Figure 3

Exhaust gas mass flow varying with time for the FTP-75 drive cycle

Figure 4

Exhaust gas temperature exiting the catalytic converter for the FTP-75 drive cycle

Figure 5

Thermal power in the exhaust gas varying with time for the FTP-75 drive cycle

Figure 6

Schematic of the multiple section TE power generator system. TEG stands for TE power generating section while V stands for valve.

Figure 7

TE power generator system with intermediate loop between the exhaust pipe and the TE generator

Figure 8

Schematic of the multiple section TE power generator system for use with an intermediate loop

Figure 9

Power output versus exhaust gas mass flow for one section and three section devices

Figure 10

Improvement in power output by using the three section system instead of the one section system

Figure 11

TE efficiency versus exhaust gas mass flow for one section and three section devices

Figure 12

Total efficiency versus exhaust gas mass flow for one section and three section devices

Figure 13

Energy recovered during the FTP-75 drive cycle versus exhaust gas mass flow for one section and three section devices

Figure 14

Total cycle energy recovered for four different drive cycles for one section and three section devices

Figure 15

Improvement in energy recovery by using the three section system instead of the one section system

## Errata

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