Acoustic characteristics of looped-tube thermoacoustic refrigerators with external and in-built acoustic drivers: A comparative study

Thermoacoustic refrigerators (TARs) are in the first place acoustic systems. It is indispensable to conduct an acoustic analysis of the entire system before a thermodynamic analysis of the thermoacoustic core. This study focuses on the acoustic characteristics of looped-tube TARs integrated with single (or dual) external (or in-built) acoustic driver(s). System-level acoustic models are established for the looped-tube TARs, and their acoustic performances are discussed and compared. Results show that looped-tube TARs with a single acoustic driver have a standing-wave acoustic field no matter whether the configuration is symmetric or not. The eigenmodes of the TAR are not influenced by the location of the external acoustic driver but are affected by the location of the in-built acoustic driver. New pairs of resonance and anti-resonance frequencies show up for TARs with an asymmetric configuration. Compared with looped-tube TARs with a single external (or in-built) acoustic driver, looped-tube TARs with dual external (or in-built) acoustic drivers have the same (or different) eigenmodes. A standing-wave acoustic field is present inside the loop only when the two acoustic drivers work in in-phase and anti-phase modes. At other phase differences between the two acoustic drivers, the acoustic field inside the loop becomes hybrid, containing both standing- and traveling-wave components. The theoretical methodology and analytical results in this study are valuable in comprehending the acoustic behavior of electrically-driven looped-tube TARs, providing useful guidelines for the active control of acoustic field and heat transport in the thermoacoustic core.