Dynamic piezo-thermoelectric generator for simultaneously harvesting mechanical and thermal energies

In recent decades, the development of eco-friendly technology has attracted tremendous attention due to the energy crises and environmental issues in modern society, especially for the enhancement of energy efficiencies and the energy harvesting of secondary or waste energies. Conventional approaches in the energy recovery of industrial waste heat mainly focus on heat scavenging, whereas the kinetic energy is neglected. Nonetheless, mechanical/kinetic energy harvesting of the heating fluid has a critical effect on the power density improvement of waste energy utilization. Herein, a dynamic piezo-thermoelectric generator (dPTEG) prototype is designed and fabricated based upon the Brayton cycle system and demonstrated for the simultaneous harvesting of low-grade mechanical and thermal energies. In this dPTEG, radial PVDF-based piezoelectric generators (PEG) and annular BiTe-based flexible thermoelectric generators (TEG) are used to simultaneously utilize the mechanical and thermal energies of working fluids. PEG and TEG energy converters are optimized from energy flow and thermal-electrical equivalent circuit model perspectives to illustrate the mechanical-thermal-electrical coupling of piezo-thermoelectric energy recovery. The length-specific power of the dPTEG with series and parallel connections of 55 μW/cm and 19 μW/cm, respectively, are achieved under steady-state flow (473 cm/s and 4 K temperature difference). Moreover, the series and parallel electrical outputs are improved by 35% and 158%, respectively, compared with traditional single TEG energy conversion under similar working conditions. These results indicate that the dPTEG presented here offers a feasible solution to utilize the low-grade mechanical/thermal energy and industrial waste heat of heating fluids. Additionally, the long-time stability and reliability evaluation of the dPTEG further verifies the potential application of this system in day/night environments with multi-range temperatures and flow rates.