A heat pump that uses sound to cool is three times as efficient as previous designs. The system engineered at Technion-Israel Institute of Technology in Israel relies on sound waves to change temperature instead of mechanical components, which require greater energy inputs to manipulate. Previous attempts to design thermoacoustic heat pumps have not resulted in units with exceptional efficiency or powerful enough to be useful.

The new phase change thermoacoustic heat pump described in Energy Conversion and Management consists of a metal tube filled with nitrogen connected on one end to a loudspeaker that plays a sound roughly 100 times more powerful than the noise from a chainsaw. The sound waves cause the nitrogen to compress and expand, and the gas cools as it expands toward the loudspeaker end of the tube.

The phase-change thermoacoustic heat pump consists of a loudspeaker, a stack sandwiched by a cold heat exchanger and an ambient heat exchanger, and a resonator. The symbols ‘CHX’ and ‘AHX’ denote the cold heat exchanger and the ambient heat exchanger respectively. ‘P’ and ‘T’ represent pressure sensors and thermocouples respectively. Source: Guy Z. Ramon et al./ Technion-Israel Institute of Technology

The design 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, producing vapor in a process that releases energy and cools the gas further. The process can be reversed to generate heat rather than remove it.

For every unit of power consumed, the heat pump can remove up to four times that much heat, comparable to household air conditioners and representing a threefold improvement on past thermoacoustic devices.

The research was presented at the 75th Annual Meeting of the Division of Fluid Dynamics of the American Physical Society, held in November 2022 in Indianapolis, Indiana.