Study of the effects of axial conduction on the performance of thermoelectric generators integrated in a heat exchanger for waste heat recovery applications

The electrical power generated from thermoelectric generators (TEGs) integrated in a heat exchanger is maximized by applying novel heat exchanger design criteria for waste heat recovery systems. A numerical model is developed and experimentally validated to simulate the performance of TEG-integrated heat exchangers. The performance of a heat recovery system, suitable for low temperature commercial applications ~300 °C, is investigated for a range of heat exchanger sizes of 2 to 8 TEG rows and exhaust gas mass flow rates of 0.02 to 0.08 kg/s. The adverse effect of the heat conducted axially, along the flow direction, on the total power output of the TEGs is quantified. The number of rows reaches an optimum value for a given gas flow rate beyond which a significant drop in the hot-side temperature of the upstream TEG rows occurs due to the increase of the axial conduction between successive rows. The term “Power Gain” is introduced in this study as the ratio between the power output from a system without axial conduction to that with axial conduction. Power Gain shows the potential benefits of limiting the axial conduction through the heat exchanger and values up to 1.2 times (20% increase in power) can be obtained for relatively low exhaust gas flow rates (~0.02 kg/s). Novel performance maps are developed to correlate the power output with the heat exchanger design, exhaust gas flow rate and number of TEGs. Such maps can be used to guide the optimization of the design of TEG-integrated waste heat recovery systems.