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

Nature Energy volume 6, pages 260–267 (2021)Cite this article

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Abstract

Conventional refrigeration relies on hazardous agents, contributing to global warming. Soft, cheap, biodegradable solid-state elastocaloric cooling based on natural rubber offers an environmentally friendly alternative. However, no such practical cooler has been developed, as conventional soft elastocaloric designs are not fast enough to ensure adiabaticity. Here, 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 designs. Negligible heat exchange in expansion/contraction stages combined with the latent heat of phase transitions results in a giant elastocaloric crystallization effect. The rubber-based all-soft heat pump enables a specific cooling power of 20.9 W g–1, 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 set-up, opening up the opportunity of a viable plug-in-ready cooling device.

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Fig. 1: Illustration of the geCC effect in elastomers, heat pump design principle and performance comparison.
Fig. 2: Elastic and thermal properties of a NR membrane and resulting cooling performance of the heat pump.
Fig. 3: Adiabatic snap-back cooling.
Fig. 4: Actuated cooler design, characteristics and thermal properties.

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Data availability

The datasets generated and/or analysed during the current study are available within the paper and its Supplementary Information. Other materials are available from the corresponding author, M.K., upon reasonable request.

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Acknowledgements

We dedicate this work to S. Bauer. This work was supported by the ERC Starting Grant ‘GEL‐SYS’ under grant agreement no. 757931 and start-up funding of the Linz Institute of Technology ‘Soft Electronics Laboratory’ under grant no. LIT013144001SEL.

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Author notes

  1. Deceased.

Authors and Affiliations

  1. Division of Soft Matter Physics, Institute for Experimental Physics, Johannes Kepler University Linz, Linz, Austria

    F. Greibich, R. Schwödiauer, D. Wirthl, M. Drack, R. Baumgartner, A. Kogler, J. Stadlbauer, S. Bauer, N. Arnold & M. Kaltenbrunner

  2. Soft Materials Lab, Linz Institute of Technology, Johannes Kepler University Linz, Linz, Austria

    F. Greibich, R. Schwödiauer, G. Mao, D. Wirthl, M. Drack, J. Stadlbauer, N. Arnold & M. Kaltenbrunner

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Contributions

F.G. and R.S. designed and fabricated the geCC heat pump and the DEA-triggered cooler and performed all experiments and measurements associated with these devices. R.B., A.K. and R.S. performed the infrared measurements. F.G., M.D. and G.M. performed the tensile tests. G.M. conducted the simulation; N.A. developed the theoretical framework.; and F.G., R.S. and N.A. analysed data. F.G., D.W., M.D. and G.M. prepared figures, and D.W., F.G. and G.M. prepared videos with contributions from all authors. F.G., N.A., R.S. and M.K. wrote the manuscript with comments from all authors. G.M., D.W., R.S. and J.S. contributed to editing the manuscript. S.B., R.S., N.A. and M.K. supervised the project.

Corresponding author

Correspondence to M. Kaltenbrunner.

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The authors declare no competing interests.

Additional information

Peer review information Nature Energy thanks Manfred Kohl and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary information

Supplementary Information

Supplementary Notes 1–9, Figs. 1–10, Table 1 and references.

Supplementary Video 1

Infrared camera side view of the inflation and deflation of a NR balloon. The balloon heats above the background temperature during the inflation snap-through and cools below this temperature during the deflation snap-back. This video illustrates the principle of geCC-based cooling with a NR membrane. The temperature changes are smaller than in the much faster cycling experiments with the LTR and HTR, which are absent here.

Supplementary Video 2

Side view of the cyclic snap-through inflation and snap-back deflation of a NR balloon. The fully deflated balloon membrane rests on the LTR with a prestretch of λ~1.4 and inflates rapidly up to the contact with the HTR, where the balloon remains for a fraction of a second with a minor excess overpressure, providing good thermal contact and temperature equilibration before the snap-back.

Supplementary Video 3

Infrared camera top view of the inflation and deflation of the NR balloon, similar to (but different from) Supplementary Video 1. Inflation temperature changes are underestimated, due to the semitransparency of the thin inflated balloon and relatively slow inflation rate. Deflation snap-back takes less than 100 ms (Fig. 2b) and is almost adiabatic. Snap-back temperature changes were used in calculations, as explained in the Supporting Information. Due to the contribution from the SIC, these temperature changes are about two times larger than expected from pure elastocaloric consideration, resulting in a geCC effect. One can see the inhomogeneity of the temperature distribution and gradual thermal equilibration with the background, which is much slower than in cycling experiments due to the absence of the LTR and HTR.

Supplementary Video 4

NR balloon actuated by voltage-controlled DEAs (Supplementary Fig. 9). This design avoids complex pneumatic parts and allows for a low-noise and extremely fast cycling operation (up to 3 Hz). Prior to actuation, both the DEA and the NR balloon are inflated with a constant offset pressure. For continuous operation, a high-voltage sine-wave signal is applied to the DEA electrodes. The high number of DEAs is needed to achieve the necessary volume change of the NR balloon.

Supplementary Data

Electrical input power of the elastomer actuator for all individual runs of Supplementary Fig.10, used to calculate mean power consumption and standard deviation.

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Greibich, F., Schwödiauer, R., Mao, G. et al. Elastocaloric heat pump with specific cooling power of 20.9 W g–1 exploiting snap-through instability and strain-induced crystallization. Nat Energy 6, 260–267 (2021). https://doi.org/10.1038/s41560-020-00770-w

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