A highly efficient eco-friendly heat-driven thermoacoustic refrigerator using nitrogen and water

The heat-driven thermoacoustic refrigerator (HDTR) represents an emerging, environmentally friendly cooling technology known for its high reliability. However, its efficiency is currently lower than that of commercial absorption refrigerators. This study introduces an innovative, highly efficient HDTR using nitrogen and water as eco-friendly and economical working substances. A key feature of this system is the inclusion of a bypass tube, which ensures efficient acoustic power matching between the engine and cooler units at elevated heating temperatures, thereby markedly enhancing efficiency. Firstly, we investigate the bypass mechanism, revealing a constraint on heating temperature in traditional direct-coupling systems, which impedes efficiency improvement. The integration of a bypass tube eliminates this constraint, leading to a significant enhancement in coefficient of performance (COP) at high heating temperatures. Subsequently, the operating performance of this novel system is numerically analyzed. For standard air-conditioning applications, the system achieves a cooling power of 5.19 kW, a COP of 1.79, and a relative Carnot efficiency of 26.2 % at a heating temperature of 700 °C. Further comparative analysis suggests that this system has the potential to outperform direct-fired absorption refrigerators in terms of COP, underscoring its substantial promise in the realm of room-temperature heat-driven refrigeration.