Conformal heat energy harvester on Steam4 pipelines for powering IoT sensors

This paper discusses a novel design and analysis of a conformal thermoelectric generator (cTEG), which can be used for powering the internet-of-things (IoT) wireless sensors for continuous monitoring of steam pipelines operation and maintenance. This conformal device is designed to be directly attached to a cylindrical steam pipe, therefore has a mechanical flexibility to bending align to the pipe curvature (conformality), and which transports superheated steam at 200 degrees C or around. Lack of continuous monitoring of underground pipelines have resulted in a significant loss of money, time, and resources. This primarily is due to limited access for reading data or replacing batteries. This issue can be addressed using cTEG which can directly convert wasted heat from pipeline to electricity for continuous powering of IoT sensors. The cTEG can be made from a classical bulk bismuth telluride (Bi2Te3) for sintered TEG legs. In the analysis, the material properties of the legs are expected be constant and independent to the temperature where the figure-of-merit is near 1.0 at room temperature. A rollto-roll thermoelectric module is considered by using Kapton film as the substrates with PDMS for filling the gap to achieving low cost and high performance. The electro-thermal device optimization was conducted by using analytical model. Available heat flow in the system is determined by the device design and the hot and cold side heat exchange. Hence these heat transfer limit the power output per device footprint. The moderate passive air convection can be enhanced by extending surface areas by fins to improve the power output. This work particularly focused on the optimization of the module design while the thickness is limited by the requirement of maintaining the mechanical conformability to a pipe surface. Variational conditions (steam temperature, flow rate, pipe diameter) and design parameters (fill factor and leg length) were investigated. In addition, this approach can be applied to other TEG designs with such dimension limitations. The upper limit of power output per device footprint is found at 19.5 W/m2 with fill factor of 20%, where cTEG could achieve to 35 W/m2 at the optimum with few centimeters thickness. The material cost to manufacture the cTEG was estimated and was found to be closer to a comparable range of the first set of primary batteries. The novel modeling method presented here can also be applied to other energy-related fields, such as geothermal, deep sea monitoring field in which heat and electricity co-optimization is of vital importance.