Research paper of the month
March 2015 - Too cool to work
This Commentary presents an original analysis that investigates how energy efficient it is to drive thermal changes near phase transitions in magnetocaloric and electrocaloric materials. For this, we applied the definitive 1956 treatment of electrical work and mechanical work to modern materials that have been proposed for cooling applications. We were extremely privileged to do the academic work with Volker Heine, six decades after he wrote the paper on which we built.
Our finding is that magnetocaloric materials driven using the magnetic field from a permanent magnet are more energy efficient than electrocaloric materials driven using an electric field generated by charging capacitor plates. However, this discrepancy disappears if the electrical energy used to drive electrocaloric effects is recovered. For the application of electrocaloric materials, this recovery of electrical energy should prove important.
Figure: Energy efficiency η describes the heat Q divided by the work W that is done to drive magnetocaloric (MC) and electrocaloric (EC) effects. Mechanocaloric (mC) effects due to stress are also included. The Commentary also shows images of very recent prototype coolers based on EC and mC effects.
X. Moya, E. Defay, V. Heine and N. D. Mathur, "Too cool to work", Nature Physics, 2015.