Heat Pump Uses a Loudspeaker and Wet Strips of Paper to Cool Air
upstart writes:
Heat pumps cool buildings by removing heat from the inside and pushing it outside, like a refrigerator. But unlike a refrigerator, they can also heat an enclosed area by reversing the process. To top it off, heat pumps are typically more efficient than conventional heating and cooling devices.
[...] The team's thermoacoustic heat pump consists of a metal tube filled with nitrogen connected on one end to a loudspeaker that plays a sound roughly a hundred times more powerful than the noise from a chainsaw. The sound waves cause the nitrogen to compress and expand. When the gas is allowed to expand toward the loudspeaker end of the tube, it gets cool, much like how perfume sprayed from a mister cools as it dissipates.
"Inside of the tube it's as loud as rock and roll. Outside, it is dead silent," says Ramon.
Other thermostatic heat pumps work similarly, but the new one also uses water via a stack of wet paper strips placed at the other end of the tube. When the nitrogen condenses and expands, it evaporates some of this water and the turns it into vapour. This process releases energy and cools the gas further.
The whole process can also be run in reverse to generate heat rather than remove it.
[...] Simone Hochgreb at the University of Cambridge, who was not involved in the project, says that this kind of thermoacoustic device is promising because it may be efficient enough to run entirely off solar power. However, there is a trade-off. One benefit of thermoacoustic devices is that they are relatively simple to assemble because the only moving part is a loudspeaker. Adding the stack of wet strips makes the pump more efficient but also more complicated to manufacture, she says.
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