Ultra-efficient thermoacoustically-driven refrigeration: Detailed mechanism and optimization analysis

Thermoacoustically-driven refrigerator (TDR) represents a new sustainable cooling technology with advantages of environmentally friendliness, no moving components, and long life. However, the relatively low efficiency hinders its extensive application. This study deeply investigates a new TDR with bypass exhibiting a significantly higher coefficient of performance (COP). The efficient operation mechanism is initially comprehensively explored, including the analyses of power-matching principle, acoustic field and loss distribution. It is revealed that the bypass design overcomes the constraint of heating temperature, thus remarkably improving efficiency. Employing a dimensionless matching factor can estimate the power-matching degree under given conditions. A better acoustic field explains the system's higher COP, mainly attributed to larger dimensionless acoustic impedance amplitude in the regenerators. Subsequently, we design bypass-typed TDR systems for different working gases and investigate their performance at high heating temperatures. At standard air-conditioning cooling conditions, the present systems display ultra-high COPs of 3.24, 2.97, and 2.61 at a heating temperature of 1226 °C with working gas of hydrogen, helium, and nitrogen, respectively; further optimization yields a maxixum of 3.29 for hydrogen, exhibiting bright prospect in heat-driven refrigeration. This work provides deeper insights on the efficient operation mechanism of the TDR with bypass, expands its application to higher heating temperatures and further enhances its COP to ultra-high values.