Converting low-grade heat into mechanical energy using a natural rubber elastocaloric device

Abstract

This work leverages the thermomechanical properties of natural rubber, an abundant, low-cost, and renewable material, for low-grade heat energy harvesting. Natural rubber tubes exhibited temperature-induced stress variations of 10 kPa.K⁻¹ when pre-elongated to 5 times their original length, for a temperature range of 20°C to 60°C. A prototype elastocaloric device was evaluated using a fluid to cyclically transfer heat from a hot heat exchanger to the natural rubber and then to a cold heat exchanger. Constitutive equations and simulations were used to assess the energy conversion capability. Finally, thermodynamic energy cycles were experimentally tested with temperature variations of 35 K and elongations of 4.5–5.5 times the original length, converting heat-to-mechanical work at 4 J per cycle, corresponding to 150 mJ.cm⁻³. The proposed design is scalable with a larger quantity of natural rubber, and after adding an electromagnetic system, low-grade heat energy may be converted into electricity.