Effect of a bypass tube on the heat-driven direct-coupled Stirling refrigerator

The direct-coupled structure is novel for heat-driven Stirling refrigerators. However, the heating temperature of this structure is limited by the inherent coupling of acoustic power. To break this limitation, a bypass tube is introduced for transmitting part of the acoustic power directly to the refrigeration unit without being amplified by the engine unit. Therefore, a higher heating temperature could be applied to improve the efficiency. Based on this, a heat-driven direct-coupled Stirling refrigerator with a bypass tube is proposed and simulated by a verified numerical model. The results show that, with the geometry parameters being optimized to reach an optimal bypass ratio, the performance of the system can be significantly improved with the increased heating temperature, which could be lifted from about 500K to at least 1000K. In an optimal case, the system can achieve a cooling capacity of 5000W with COP of 1.83, when the heating, ambient and cooling temperatures are 1000K, 308K and 280K, respectively. Besides, suppressing Gedeon streaming existing in the toroidal structure composed of the engine unit and the bypass tube is necessary. ... mehrThis paper demonstrates the effectiveness of the bypass tube to improve the performance of heat-driven direct-coupled Stirling refrigerators.