Bistability-enhanced elastocaloric cooling device based on a natural rubber foil

A novel solid-state elastocaloric cooling device is presented, making use of a bistable actuation mechanism for loading of a natural rubber (NR) foil refrigerant. The thicknesses of the foil refrigerants are 290 and 650 μm in an initial undeformed state, while their lateral size is 9 × 26.5 mm$^2$ . Owing to the large surface-to-volume ratio of the NR foils, heat transfer to the heat sink and source is accomplished by a solid–solid mechanical contact. The loading mechanism consists of a rotating lever arm providing for stable positions at contact to the heat sink and source, which allows for significant power saving during elastocaloric cycling. In addition, the negative biasing associated with bistability favors good thermal contact at the end positions, which improves heat transfer resulting in a maximum temperature span ΔT$_{device}$ of
4.2 K in the strain range of 300%–700% under adiabatic conditions. The coefficient of performance of the device COP$_{device}$ reaches values up to 5.7 for foil refrigerants of 290 μm thickness. The maximum cooling power is 214 mW corresponding to a specific cooling power of 3.4 Wg$^{−1}$.