## 2 Materials and Methods  
### Low-Cost TA-SLiCE  
The investigation was conducted utilizing an experimental TA-SLiCE. This engine was designed and manufactured in accordance with the guidelines outlined in [5]. This section introduces its design modifications, with a focus on optimizing the components to achieve a main objective: making TA-SLiCEs easily reproducible for low-power applications. The configuration of the TA-SLiCE investigated in [5] and in the present study is similar to the 3D model developed using computer-aided three-dimensional interactive application software (CATIA V5 6R2019, Dassault Systemes, Ile-de-France, France) depicted in Figure 2. The regenerator is a screen made of stainless steel with 40 openings per inch and a 0.44 mm wire diameter. The TA-SLiCE illustrated in Figure 2 was firstly modelled using the Design Environment for Low-Amplitude Thermoacoustic Energy Conversion DeltaEC Software (DeltaEC Release 6.4b2.7, Los Alamos National Laboratory, Los Alamos, NM, USA) [20], which relies on [PERSON]'s linear theory [4], to search for the optimal design operating at 23 Hz with air at  
Figure 2: A 3D model of the experimental TA-SLiCE used in this work, developed with CATIA V5 software, incorporates several design modifications, including grey acrylonitrile-butadiene-styrene (ABS) components and O-ring grooves. The sleeves (blue) and flags (silver) are manufactured in aluminum. atmospheric pressure and keeping the heat source and heat sink temperatures at around 641 K and 296 K, respectively. DeltaEC offers valuable insights into acoustic field properties, assuming a linear acoustic approach with features like plane waves, laminar flow, and no streaming. These simulation details are fully explained in [5]. For the TA-SLiCE used in this paper, some design modifications were implemented with respect to previous versions:  
* Manufacture using acrylonitrile-butadiene-styrene (ABS) and sealing with acetone. Three-dimensional fused deposition modeling (FDM) was used to manufacture the components of the TA-SLiCE. This provides high flexibility in constructing all its elements, enabling quick evaluation of each design regardless of complexity. The choice of ABS over the commonly used polylactic acid (PLA) is not due to the former's mechanical properties but its superior post-processing for achieving the necessary seal for this application. The key reason is ABS's easier post-treatment compared to PLA, which, to ensure sealing, requires specific chemicals like tetrahydrofuran (THF), ethyl acetate, butanone, dichloromethane (DCM), chloroform, etc. These industrial solvents can be hazardous if not handled and used properly. In contrast, applying a layer of acetone for ABS post-processing is sufficient to ensure complete sealing after the compounds react. This approach also offers the flexibility to print sectioned parts that can later be welded together using acetone, significantly easing the printing process. This is particularly beneficial for achieving better layer deposition in components requiring 100% infill. * Incorporation of nitrile-butadiene-rubber (NBR) O-rings in the element connections in order to isolate cavities and avoid fluid leaks. The addition of O-ring grooves facilitates the easy assembly and disassembly of the engine. Previously, the use of sealing paste made this process challenging. NBR O-rings were incorporated to prevent air leaks through the Pyrex thermal buffer tube (TBT) and cooling jackets, and at the ends of the cooling jackets to prevent water from the cooling system from penetrating into the engine. This design consideration enhances both the operational efficiency and maintenance convenience of the engine, ensuring airtight seals where necessary while allowing for straightforward component adjustments or replacements. The compression needed for effective sealing is provided by mechanical joints using screws and nuts located in the refrigerators themselves, along with aluminum compression rings.