Graphite plates for enhanced high-temperature stability and thermal uniformity in thermoelectric generators applied to range-extending engine

Thermoelectric generators offer a promising solution for automotive exhaust heat recovery, particularly in range-extending engines operating under steady-state conditions. However, their performance is significantly hindered by two major thermal challenges: high exhaust temperatures and pronounced temperature gradients along the exhaust flow, both of which conflict with the narrow optimal operating window of commercial bismuth telluride thermoelectric modules. This study introduces the integration of anisotropic graphite plates between the heat exchanger and thermoelectric modules to simultaneously address these issues. The graphite plates exhibit exceptionally high thermal conductivity in the in-plane (X/Y) direction, enabling effective temperature homogenization, while their low conductivity in the through-plane (Z) direction helps maintain optimal module operating temperatures. All experimental and simulation results were obtained using a controlled coolant temperature of 285 K to maximize thermoelectric conversion efficiency. Both experimental and numerical results demonstrate that this configuration stabilizes module temperatures below 523 K, improves temperature uniformity across the module array, and achieves a maximum power output of 611 W, 44 % higher than the baseline configuration without graphite plates. The thickness of the graphite plates plays a critical role in balancing thermal management and power output. Thinner plates (e.g., 1 mm) fail to sufficiently mitigate high temperatures, leading to thermal failure, while thicker plates (e.g., 3–4 mm) reduce temperature gradients along flow direction but introduce excessive through-plane thermal resistance, diminishing power output. The 2-mm graphite plate emerges as the optimal configuration, achieving the best compromise between temperature uniformity and power generation.