Elastocaloric heat pump with specific cooling power of 20.9 W g–1 exploiting snap-through instability and strain-induced crystallization

Abstract

Conventional refrigeration relies on hazardous agents, contributing to global warming. Soft, cheap, biodegradable solid-state elastocaloric cooling based on natural rubber offers an environmental friendly alternative. However, no such practical cooler has been developed, as conventional soft elastocaloric designs are not fast enough to ensure adiabaticity.In this work, we combine snap-through instability with strain-induced crystallization and achieve a sub-100 ms quasi-adiabatic cycling which is 30 times faster than previous design.Negligible heat exchange in expansion/contraction stages combined with the latent heat of phase transitions result in a giant elastocaloric crystallization effect. The rubber-based all-soft heat pump enables a specific cooling power of 20.9 W/g, a heat-flux of 256 mW/cm 2 , a coefficient of performance of 4.7 and a single-stage temperature span between hot and cold reservoirs of 7.9 K (full adiabatic temperature change of rubber membrane exceeding 23 K).The pump permits a compact all-soft voltage-actuated setup, opening up the opportunity of a viable plug-in-ready cooling device.

Body Temperature-Triggered Mechanical Instabilities for High-Speed Soft Robots

“…During the rapid snap-through, the membrane quasi-adiabatically heats by several degrees. 8 As it thermalizes back to room temperature, the elastomer softens proportionally, 17 slightly increasing the balloon volume, which can be seen in Figure 2b , after the point 3. The gas entering the balloon somewhat cools down semi-adiabatically, but the pressure corrections in Equations (3) and (4) remain small, as long as .…”

“…If the balloon is inflated and deflated several times, the rubber membrane is cyclically loaded, revealing material-dependent effects. First, the elastomer membrane shows an intrinsic hysteresis due to stretch-induced crystallization, 8 , 18 so that different curves in the p - V plane are followed for inflation and deflation. 6 Furthermore, natural rubber softens appreciably during the first loading cycles ( Fig.…”

“…We further simplify this for a ¼ v=c < < 1, which holds in the sound limit and is fulfilled for our numbers, see the estimations below Equation (8). Furthermore, as R ¼ vt ¼ aw=(a À 1), we can replace w=w 0 ¼ t=t 0 , where t 0 ¼ R 0 =v is the starting time for the expansion, where w ¼ 0.…”

“…6 In this study, we introduce a new design for soft actuators based on the mechanical instability that occurs during the inflation of a balloon made out of a natural rubber membrane. [6][7][8] The abrupt change in the balloon size is triggered by the liquid/gas phase transition of a low-boiling point fluid. 9 This combination of instability and phase transition enables fast switching operations within a few milliseconds.…”

Magnetocaloric Effect in Flexible, Free-Standing Gadolinium Thick Films for Energy Conversion Applications

“…Recently, flexible caloric films paved the way to an alternative paradigm. In the new generation of energy transducers, based on poly(vinylidene fluoride) (PVDF) electrocaloric and natural-rubber elastocaloric materials [45][46][47][48], regeneration is replaced by a cascade of devices, whereas heat transfer is dealt with through solid-solid direct contact, making heat exchange fluid and the pumps redundant.…”