Three-stage cascaded loop-type thermoacoustic cooler for deep waste heat recovery: Achieving 77 K cooling with 45.8% recovery efficiency

With the large-scale discharge of industrial exhaust-gas waste heat, developing efficient and reliable waste-heat recovery technologies is of significant energy and environmental importance. Thermoacoustic cryocooler, featuring a simple structure, no moving parts, and the capability to make direct use of exhaust heat, provides a promising route for converting waste heat into low-temperature cooling. However, studies concerning thermoacoustic systems under liquid nitrogen temperature conditions for heat recovery remain scarce. The system is designed with a loop structure in which three engines are serially coupled to a cryocooler. A cascade (graded) heat utilization strategy is proposed, and the performance of a cascaded cryogenic refrigeration system based on this strategy was evaluated using both numerical simulations and experimental investigations. Systematic investigations were carried out to clarify how the hot heat-exchanger temperature and charging pressure affect the refrigeration characteristics. Test results showed that the cryocooler could attain a minimum temperature of 77 K at 85 Hz with the three-stage thermoacoustic engines heated to 735 K and a total heating power input of 1760 W, together with a cooling power of 3.09 W at 85.8 K. Under the three-stage cascade waste-heat utilization scheme, the waste-heat recovery efficiency reaches 45.8%, and the cooling power is 1.36 W at 83.6 K. These findings demonstrate the feasibility and application potential of the proposed system for cascade waste-heat utilization.