Modular Stacks for Acoustic Refrigeration: Investigating the Impact of Small Air Layers in a Modular Stack

A key component in acoustic refrigerators and engines is the stack, a porous material strategically placed within a tube to harness the thermoacoustic effect. 3D printing technology for stack construction is promising due to its ability to provide accurate geometry control. One potential application is the construction of modular stacks, which could facilitate experimental studies on optimal stack length, integration of thermosensors along the stack, and printing time reduction. However, the construction of modular stacks introduces the potential for small air layers between the individual modules of the stack. This study explores the potential effects of those thin air layers between the parts of a modular stack. A numerical model of a thermoacoustic refrigerator, specifically a quarter-length resonator, was implemented based on the 1D thermoacoustic software DeltaEC. Our findings reveal that the presence of air gaps has a detrimental impact on the temperature difference achieved between the two ends of the stack. However, in the considered acoustic refrigerator configuration, small gaps below 1 mm result in a decrease below 1% of the temperature span. For the considered application and tolerances of the modular stack, the effect of the air layers could be negligible; this result opens the possibility of constructing these modular stacks. Further research is needed to corroborate these effects experimentally.