Electrocaloric effect

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The electrocaloric effect describes the property of certain electrocaloric materials to react to changes in the electrical field strength in the material by cooling or heating. The cause is not known in detail at the structural level. Presumably the crystal structure changes : in that polar molecules arrange themselves in the direction of the field and heat the material or, when the field is switched off, fall back into the disordered state (increase in entropy ) and cool the material. The effect can be explained if one assumes that the entropy of the charges aligned or displaced by the E. field is reduced and has to be compensated for by increased lattice vibrations because of the constant total entropy with adiabatic changes. This results in a higher temperature. After the discharge, however, there is a cooling off.

The reverse of the effect, i.e. H. the generation of a voltage change by changing the temperature is the pyroelectric effect that is important in sensor technology .

The special feature of the electrocaloric effect is that - in contrast to the Peltier effect - cooling is possible regardless of the level of the current . The charging and discharging of the dielectrics requires a current. However, this has the character of an alternating current with a high proportion of reactive current and can therefore largely be recovered if it is not available as thermal energy after charging. The temperature difference does not have to be applied against the heat conduction taking place in a material.

With this effect, heat transport is only possible because the dissipation or supply of thermal energy is synchronous with the charge / discharge cycle. This can be done, for example, with liquids, which are always brought in when the heat energy can be released or absorbed.

The effect has been known since the 1950s and research has since improved significantly. A technical implementation failed for a long time due to the low practical efficiency. Similar to the Peltier effect, a technological application could be in cooling electronic components or in small portable applications. In particular, opportunities are also discussed to use it to cool effectively without refrigerants .

Electrocaloric materials are e.g. B. Metal oxide compounds such as lead zirconate titanate (PbZr 0.95 Ti 0.05 O 3 , short: "PZT"). In the temperature optimum at 220 ° C, a temperature difference of 12 K was achieved in 2006 - but this dropped to just 2 K at 100 ° C.

In 2017, the University of California succeeded in using a 5 mm thick construction based on a polymer sandwich structure and carbon nanotubes to cool a smartphone battery with a temperature of around 50 ° C by 8 K in a few seconds.

A project started in 2019 aims to achieve a heat output of 100 watts with a temperature difference of 30 K within four years of research and development. This shows that the effect in terms of practical application is far behind established processes ( refrigeration machine , Peltier cooler ).

See also

Individual evidence

  1. ^ A b Peter Fairley: A Solid-State Fridge in Your Pocket. In: IEEE Spectrum. September 14, 2017, accessed on September 21, 2017 .
  2. ↑ https://onlinelibrary.wiley.com/doi/pdf/10.1002/047134608X.W8244 J. Webster (ed.): Electrocaloric Effect: Theory, Measurements and Applications , in Wiley Encyclopedia of Electrical and Electronics Engineering 2015, accessed 8 December 2019
  3. ↑ Defay, E., Faye, R., Despesse, G. et al .: Enhanced electrocaloric efficiency via energy recovery. Nature Communications 9, 1827 (2018) doi: 10.1038 / s41467-018-04027-9 of May 8, 2018, accessed on Dec. 8, 2019
  4. ↑ https://www.researchgate.net/publication/304027397_Efficient_Cooling_System_Using_Electrocaloric_Effect Hirasawa, S .; Kawanami, T .; Shirai, K .: Efficient Cooling System Using Electrocaloric Effect , in  Journal of Electronics Cooling and Thermal Control 06 (02), pp. 78-87, January 2016, DOI: 10.4236, accessed on December 8, 2019
  5. ↑ Andreas Stiller: Possible new cooling technology for chips. In: heise.de. March 3, 2006, accessed September 21, 2017 .
  6. ↑ Holger Kock: Fraunhofer starts development of refrigerant-free, energy-efficient electrocaloric heat pumps , press release from the Fraunhofer Institute for Physical Measurement Techniques , accessed on December 8, 2019