Experimental and Modeling Study of a Heat Exchanger Concept for Thermoelectric Waste Heat Recovery from Diesel Exhaust

Approximately one-third of the fuel energy consumed by an internal combustion engine flows out the tailpipe as waste heat. Thermoelectric devices are being considered as a means of utilizing some of this waste heat to generate electric power on vehicles. A 1.1-liter volume flat plate heat exchanger was fabricated to study the heat transfer characteristics of a conceptual design for thermoelectric waste heat recovery from diesel exhaust, and used to validate a heat exchanger model. The heat exchanger consisted of an exhaust channel and two coolant channels all having rectangular cross-sections. The experimentally measured heat transfer rates were compared with a finite element heat transfer model to be used both for heat exchanger development and modeling thermoelectric device performance. In both the model and the experiment, alumina paper was used as a surrogate for the thermoelectric materials. The minimum and maximum heat transfer rates calculated from the model were 188 W and 1.89 kW, respectively, and the heat exchanger effectiveness from the model ranged from 0.110 to 0.169 for gas exchange rates from 65.7 s^-₁ to 334 s^-₁. The measured minimum and maximum heat transfer rates from the experiments were 385 W and 1.45 kW, with effectiveness ranging from 0.079 to 0.258. While there was good trend-wise agreement between the model and experiments, unaccounted for entrance effects and effects of measurement locations likely contributed to the observed differences between the two.