Most air conditioners and fridges rely on contracting and expanding a liquid to either absorb or release large quantities of heat. While these systems are relatively cheap and simple to produce, they aren't very efficient and require lots of energy. Besides, many of the coolants used are environmentally harmful.
Now, Emmanuel Defay at the Luxembourg Institute of Science and Technology and his colleagues have developed a coolant-free refrigeration device made from the metals lead, scandium (钪) and tantalum (钼). It can reach maximum efficiencies of more than 60%, almost double that of typical single-room air conditioning units. The technology is based on a principle called electrocaloric cooling, in which an electric field applied across a material changes the direction of electric charges, causing a temporary increase in temperature and a succeeding decrease when the electric field is removed.
To make their cooling system, Defay and his colleagues piled up eight strips of the material known as lead scandium tantalate, which is electrocaloric, on top of one another and dipped them in a heat-carrying liquid, silicone oil. When an electric field is switched on and the strips heat up, the liquid moves to the right, and when it cools down, it moves to the left, creating permanent regions of hot and cold of about 20℃difference. These regions can be used as hot and cold reservoirs from which the oil can be circulated through pipes to cool or heat rooms or objects as desired.
"Although the efficiency of the device is theoretically 67%, the efficiency of the current design is around 12%. This could be improved if a better conductor of heat than the lead scandium tantalate were found," said Defay.
"A highest performance has been achieved by combining known elements," said NeilMathur at the University of Cambridge. However, he added, the team only looked at the cooling power of the pile of metal strips themselves, while it would be interesting to see how the entire device performs together.
