6. Conclusions

two neighbouring EC rings are directly contacted to facilitate the heat exchange with each other. Heat exchangers with high thermal conductivity are placed at the circumference at opposite sides of the device to absorb or reject heat. Simulation results showed a cooling power density of 37 W/cm3 for a Tspan of 20 K for a cooling device made of P(VDF-TrFE-CFE) terpolymer.

The electrocaloric oscillatory refrigeration device (ECOR) adapts a concept known from thermoacoustic cooling [28, 73]. It consists of an EC element and a solid-state regenerator. The length of the EC module is slightly shorter than that of the regenerator, so that the EC module can move back and forth on the regenerator. Thereby, a temperature gradient is established within both and heat is transported from one side to the other. The solid-state regenerator

Refrigerant Configuration T, K E, MV/m ΔTEC, C f, Hz q\_, W/cm<sup>2</sup> Φ Ref. PST AER 1.5 0.9 4 0.05 [59]

0.9PMN-0.1PT Small scale AER 115 1.5 1.25 [42]

Ba(Zr,Ti)O3 (MLC) 20 0.54<sup>1</sup> 0.02 0.006<sup>1</sup> [73]

P(VDF–TrFE–CFE) 59.2/33.6/7.2

36 Refrigeration

P(VDF-TrFE) 68/32 (irrad.)

1

Experimental value.

Fluid-based micro-scale

refrigerator

n/a EC refrigerator with internal regenerator

> Chip scale EC oscillatory refrigerator (ECOR)

Table 6. Characteristics of EC refrigerators using regeneration.

3<sup>1</sup> 1.5<sup>1</sup> 5

260–280 6 3 0.36 [57] 280–300 1.5 0.9 0.42 [71]

50 10 0.173 [72]

0.02 5

50 0.5 [74]

160 211 10 5.4 0.5 [28]

323 150 14.6 1.25 ~4 0.57 [47]

300 150 16 10 3 0.31

50 20 2

50 0.9<sup>1</sup> 0.75

298 5 0.083

80 2.2<sup>1</sup> 0.5 100 0.5

100 3 150 0.5

308 100 1

87 1.25 300 57 0.75

25 0.6<sup>1</sup>

EC cooling is an environment-friendly caloric energy conversion technology. Cooling power densities of a few W/cm2 and temperature spans in the order of 20 K (in regeneration systems) are achievable at a cycle time of 100 ms. Currently, EC cooling does not represent an alternative for the full replacement of vapour compression. It can be assumed that it will rather penetrate niche markets in the future such as small, compact, local and all-solid-state refrigerators. Although the reverse Brayton thermodynamic cycle is actually the most suitable for practical implementation, further research on more efficient cycles is required. EC cooling processes possess a large materials efficiency and are thermodynamically reversible. At present, the bottleneck of EC refrigerators is the heat transfer process needed to absorb heat from the load and reject it to the heat sink. Most attractive for applications are all-solid-state devices including Peltier elements as thermal switches and active electrocaloric regenerators using a liquid heat transfer agent.
