Chinese Academy of Sciences developing thermoacoustic heat pump for industrial applications
An industrial furnace
Image: Photo by NIloy Tanvirul on Unsplash
A research team led by scientists from the Chinese Academy of Sciences (CAS) has developed a novel heat-driven thermoacoustic heat pump (HDTAHP) that is reportedly capable of achieving higher temperature lift and heat supply temperatures than those reached by state-of-the-art absorption heat pumps and absorption heat transformers.
“This work provides a promising solution for high-temperature industrial heat supply,” the group said. “Critically, the single-stage HDTAHP operates without moving parts, making it highly suitable for high-temperature operation. Future efforts will focus on optimizing system design to enable integration with actual heat sources and sinks, enhance the coefficient of performance for heating, and further expand its practical application prospects.”
The academics first designed the system in the Sage software, which is commonly used for thermoacoustic systems development. The system was set to include three subunits: a thermoacoustic engine unit, a thermoacoustic heat pump unit, and acoustic resonators. In the engine unit, a low-temperature heat exchanger uses two thermosyphons to release heat via water. Throughout the entire system, helium gas oscillates to transfer energy as sound.
Using Sage, they further optimized the system, with dimensions of the regenerator at the engine unit being a diameter of 110 mm, a length of 45 mm, and a wall thickness of 5 mm, while the regenerator at the heat pump unit had dimensions of 110 mm, 35 mm, and 5 mm, respectively. The compliance tubs at the acoustic resonator had a diameter of 120 mm, a length of 270 mm, and a wall thickness of 4 mm; while the resonance tube was 44 mm, 9,000 mm, and 4 mm, respectively.
“At a hot end temperature of the engine unit of 350 C and a mean pressure of 5 MPa, the system achieves a supply temperature of 270 C with a temperature lift of 125 C, which is the highest reported among all heat-driven heat pumps,” the scientists explained. “Meanwhile, a coefficient of performance for heating (COPh) of 0.41 and a relative Carnot efficiency (COPR) of 33% are achieved, corresponding to a heat supply of 1,903 W.”
The research group also found that, due to the use of thermosyphons at the cold end of the engine unit, the released heat grows steadily from 3,566 W to 4,202 W. That is, with an increase in mean pressure, while the cold end temperature remained stable around 50 C. They also concluded that with a compliance tube diameter of 120 mm, the system reaches an optimal state. In that state, the onset temperature reaches the lowest point of 74.5 C, while COPh reaches the peak of 0.36.
“An increase in the temperature lift of the heat pump unit reduces its heat pumping capacity, leading to reductions in both heat supply and COPh. However, the absorbed heat increases to maintain the cold end temperature,” they concluded. “A larger temperature difference of the engine unit improves thermoacoustic conversion, increasing the heat supply and COPh. In addition, increases in mean pressure enhance the heat-carrying capacity of the working fluid, leading to an increase in heat supply and an initial rise in COPh. However, excessively high mean pressure (exceeding 5 MPa) causes decreased COPh due to a more rapid increase in the heat absorbed by the engine unit.”
The system was presented in “A heat-driven thermoacoustic heat pump supplying heat up to 270 °C,” published in Energy. Researchers from China’s Chinese Academy of Sciences, the University of Chinese Academy of Sciences, and the Aero Engine Corporation of China (AECC) Commercial Aircraft Engine Company participated in the research.