Experimental and numerical study of a heat-driven cascade-looped thermoacoustic cryocooler working at 77 K

Thermoacoustic cryocoolers are an emerging environmentally friendly cooling technology featuring high reliability and the ability to utilize low-grade heat sources. Among various configurations, the series-connected cascaded structure is generally regarded as one of the most powerful and popular architectures at room-temperature and natural-gas temperature levels. However, experimental studies on cascaded systems operating in the liquid‑nitrogen temperature range remain scarce due to the large temperature span and challenges in acoustic field matching. In this study, a heat-driven cascaded thermoacoustic cryocooler operating in the liquid‑nitrogen temperature range is experimentally demonstrated. The system consists of three thermoacoustic engines connected in series to drive a thermoacoustic cryocooler within a common traveling-wave loop. Combined numerical simulations and experiments were conducted to investigate the cooling performance. The acoustic field matching characteristics of the engines and the cryocooler were further analyzed separately. At an operating frequency of 85.7 Hz, a minimum cooling temperature of 77 K was achieved, with a cooling power of 3.09 W at 85.84 K. These results experimentally demonstrate, for the first time, the feasibility and potential of cascaded thermoacoustic cryocoolers for liquid‑nitrogen-temperature applications. Moreover, it is found that for thermoacoustic engines with identical dimensions and working conditions, the optimal pressure ratio corresponding to maximum efficiency increases progressively with the stepwise amplification of the input acoustic power.