Harvesting electrical energy from torsional thermal actuation driven by natural convection

Shi Hyeong Kim,Dongseok Suh,Geoffrey M Spinks,Ray H Baughman,Hyeon Jun Sim,Jae Sang Hyeon,Seon Jeong Kim

doi:10.1038/s41598-018-26983-4

Abstract

The development of practical, cost-effective systems for the conversion of low-grade waste heat to electrical energy is an important area of renewable energy research. We here demonstrate a thermal energy harvester that is driven by the small temperature fluctuations provided by natural convection. This harvester uses coiled yarn artificial muscles, comprising well-aligned shape memory polyurethane (SMPU) microfibers, to convert thermal energy to torsional mechanical energy, which is then electromagnetically converted to electrical energy. Temperature fluctuations in a yarn muscle, having a maximum hot-to-cold temperature difference of about 13 °C, were used to spin a magnetic rotor to a peak torsional rotation speed of 3,000 rpm. The electromagnetic energy generator converted the torsional energy to electrical energy, thereby producing an oscillating output voltage of up to 0.81 V and peak power of 4 W/kg, based on SMPU mass.

Highlights

The development of practical, cost-effective systems for the conversion of waste heat to electrical energy is an important area of renewable energy research[1,2,3]
The shape memory polyurethane (SMPU) was chosen in order to obtain a torsional muscle that could effectively harvest small temperature fluctuations above ambient temperature as mechanical energy
The SMPU shows a high degree of strain recovery during a shape memory heat/deform/cool and re-heat cycle[23]

Summary

Introduction

The development of practical, cost-effective systems for the conversion of waste heat to electrical energy is an important area of renewable energy research[1,2,3]. We want to harvest useful electrical from very small ambient temperature fluctuations To do this using the twist-based mechanism of twisted or coiled polymer fibers or yarns requires fibers or yarns having high volumetric thermal expansion coefficients near room temperature. To achieve this goal, we used a commercially available shape memory polyurethane (SMPU) to fabricate torsional artificial muscles that provide large, fast, reversible torsional strokes. Using temperature fluctuations of about 4 °C, and a temperature difference between hottest and coldest muscle segments of just 13 °C, the generator produced a peak open-circuit voltage of 0.81 V and a peak electrical power density of 4.0 W/kg (when normalized to muscle weight)

Methods

Results

Conclusion