A simulation study of automotive waste heat recovery using a thermoelectric power generator

• An energy-harvesting system from the automotive exhaust pipe was analyzed.
• Heat is converted into electricity by using thermoelectric power generators (TEGs).
• Installing more TEGs results in a larger but quickly saturated total power.
• Downstream TEGs reduce the temperature difference across the upstream TEGs.
• The efficiency is enhanced by keeping some downstream part of the heat exchanger uncovered by TEGs.

In this work, an energy-harvesting system which extracts heat from an automotive exhaust pipe and turns the heat into electricity by using thermoelectric power generators (TEGs) was investigated. The influences of the number and the coverage rate on the heat-exchanger of the TEGs were explored via simulations. It was found that implementing more TE couples does not necessarily generate more power in total, and most of all the average power per TE couple decreases rapidly. It is because the wall temperature of the exhaust pipe drops quickly along the streamwise direction and also because the downstream TEGs contend for heat with the upstream TEGs, causing a reduction in the temperature difference between the hot and cold sides of the upstream TEGs. Furthermore, it was also found that for a given total number of TE couples, it is better to retain a portion of the heat exchanger uncovered with TE couples at the downstream side so that the downstream wall of the exhaust pipe uncovered with TE couples becomes even hotter than the upstream wall covered with TE couples. Heat is consequently conducted from the downstream wall to the upstream wall and successively to the attached TEGs; a larger total power can be thus obtained.