Experimental and computational investigation of passive heat exchangers to enhance the performance of a geothermal thermoelectric generator

Abstract

Thermoelectric devices hold significant promise for generating electricity from geothermal heat, enabling the powering of measuring equipment in remote locations without the need for moving parts. Nevertheless, most developed geothermal thermoelectric generators employ fans and pumps to enhance heat transfer, thereby compromising the robustness and reliability inherent to thermoelectricity. Furthermore, there is a lack of research on passive heat exchangers for geothermal thermoelectric generators, particularly in studying their operation under a wide range of meteorological conditions. Therefore, this paper conducts a comprehensive analysis of passive heat exchangers for the cold side of the generators. Phase-change-based heat exchangers differing in their length and fluid are studied experimentally, along with a fin dissipator. Additionally, the influence of wind velocity on heat transfer and mechanical requirements is further explored through a Computational Fluid Dynamics model. The most significant outcome is quantifying the impact of the design parameters and operational variables on the electrical production of the thermoelectric generator. Accordingly, this research aims to broaden the application of these generators to extreme environments, such as Deception Island in Antarctica. Under average operational conditions, generators incorporating 400mm water heat pipes generate 0.95W per thermoelectric module, while those incorporating heat pipes with methanol achieve an average of 0.70W. Moreover, water and methanol-based systems produce 120% and 60% more power than generators using a fin dissipator. Nonetheless, for temperatures beyond -6.5°C, water might freeze and the methanol-based heat exchangers become more suitable.