The use of environmentally harmful gases in air conditioners and refrigerators could become redundant whether a new type of heat pump keeps its promises. One prototype, described in a study published last week in Science, uses electric fields and a special ceramic instead of alternately vaporizing a refrigerant fluid and condensing it with a compressor to warm or cool the air. From a report: The technology combines a number of existing techniques and shows “exceptional performance”, says Neil Mathur, a materials scientist at the University of Cambridge, UK. Emmanuel Defay, materials researcher at the Luxembourg Institute of Science and Technology in Belvaux, and his collaborators built their experimental device from a ceramic with a strong electrocaloric effect. Materials that exhibit this effect heat up when exposed to electric fields.
In an electrocaloric material, atoms have an electrical polarization – a slight imbalance in the distribution of electrons, which gives these atoms a “plus” pole and a “minus” pole. When the material is left alone, the polarization of these atoms continually rotates in random directions. But when the material is exposed to an electric field, all the electrostatic poles suddenly line up, like hair combed in one direction. This transition from disorder to order means that the entropy of electrons – the way physicists measure disorder – suddenly drops, Defay explains. But the laws of thermodynamics say that the total entropy of a system can never decrease, so if it falls somewhere, it must increase elsewhere. “The only way for the material to get rid of this extra disorder is to pour it into the lattice” of its crystal structure, he explains. This extra disorder means that the atoms themselves start to vibrate more quickly, leading to an increase in temperature.
