The Chinese Academy of Sciences (CAS) announced this week that a group of its researchers has developed a thermoacoustic heat pump prototype capable of reaching an output temperature of over 200 C.
Acoustic heat pumps transfer heat using sound waves instead of traditional mechanical parts like compressors. A loud sound in a specially designed tube makes air molecules vibrate, creating pressure changes that move heat from one end to the other. With no moving parts, they are quieter and more durable than conventional systems, though high costs and performance limits still hinder commercial adoption.
Thermoacoustic heat pumps are a specialized type that exploits the thermodynamic interaction between sound waves and temperature changes in a stack or regenerator, offering greater efficiency and precise thermal control for certain applications.
For their prototype, the researchers used thermoacoustic Stirling heat pump (TAHP) technology, which employs sound waves in a closed gas loop to transfer heat. This system mimics a Stirling engine, a closed-cycle regenerative heat engine using a permanent gaseous working fluid, such as air or gas, where heat-driven compression and expansion create mechanical motion, with a heat transfer fluid delivering the energy as needed.
The system uses an electrical phase-switching mechanism to implement what the scientists describe as a “reverse-phase operation” of the acoustic field for the dual-acting heat pump. This design reportedly enables the reverse transmission of acoustic power within the system, allowing the high-temperature and low-temperature heat exchangers to swap functions.
The system configuration enables the compressor to operate at lower temperatures, effectively addressing the challenges of developing ultra-high-temperature compressors. “Using this approach, we successfully created the world’s first dual-acting free-piston thermoacoustic Stirling heat pump prototype capable of reaching pumping temperatures above 200 C,” the academics said. “The experimental prototype, driven by thermal energy, can pump low-grade heat energy at around 14 C to a heat source above 270 C. “
Experimental results showed that the system can raise the temperature significantly from 25 to 166 C, and that within a temperature range of 74 C, it can achieve a peak coefficient of performance (COP) of 1.68. When the ambient temperature increases to 67 C, the system provides a heating supply temperature of 214 C, with the corresponding COP and relative Carnot efficiency reaching 1.5% and 45.2%, respectively.
Looking forward, the research group intends to develop the proposed heat pump technology for high-temperature industrial processes such as petrochemicals, metallurgy, and ceramics, which have higher temperature requirements.
“For example, the heat source, which is only about 300 C for pressurized water reactors or 400 C to 500 C for parabolic trough collectors, can be increased to between 500 C and 800 C through super high-temperature thermoacoustic heat pump technology, providing a brand-new technical approach for zero-carbon high-temperature heating in heavy industry,” said the research's lead author, Luo Ercang.
The system was described in “A ultra-high-temperature free-piston thermoacoustic Stirling heat pump capable of achieving above 200 C,” published in Applied Physics Letters.
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