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Thermoacoustic stack for tri-clamp spools: Ø34.8, Ø47.5 and Ø72.9, honeycomb and spiral
What size stack does a tri-clamp thermoacoustic engine need? · Hardware · basis: Stack OD = 16 ga spool bore (34.8 / 47.5 / 72.9), exact; channel width 2–4 thermal penetration depths (δκ ≈ 0.26 mm in air at 1 bar, 100 Hz; 0.15 mm at 300 Hz), Swift
Long Earth Society build part. The stacks, driver cap and tube-length table from the LES thermoacoustic builds; the infill trick is LES's. The engines
Exact dimensions. Every file is drawn at true size with no printing tolerance. The holes and pins that meet another part are listed below under Mating features, with the fit each joint needs; open those by your printer's or process's clearance before making the part. Mating features
- sizes
- 3 in table
Notes
- The stack is the core of a standing-wave thermoacoustic engine: many narrow parallel channels between a hot face and a cold face, sitting in the resonator tube. It is drawn at the spool bore, so it is held in the bore itself.
- Honeycomb stack (1.5 and 2 in, × 40): hexagonal cells 1.5 mm across flats with 0.4 mm walls, every cell whole inside a 0.4 mm outer ring. Spiral stack (all three sizes, × 30, 40 and 50): one 0.4 mm wall wound with a 1.0 mm gas gap from a Ø6 core to a 0.5 mm outer ring.
- Channel size: half-width 2–4 × δκ, δκ = √(κ / (π f ρ cp)), so about 1–1.5 mm channels at 100 Hz and about 1.0 mm at 300 Hz in air at 1 bar.
- Placement: centred about λ/8 from the closed (hot) end of a λ/4 resonator; a closed-open tube resonates at f = c / 4L (150 Hz → 572 mm, 300 Hz → 286 mm in air at 20 °C).
Sizes
| spool_in | stack_od_mm | forms | lengths_mm | quarter_wave_150hz_mm | half_wave_150hz_mm |
|---|---|---|---|---|---|
| 1.5 | 34.8 | honeycomb 1.5 mm cells / spiral 1.0 mm gap | 40 / 30, 40, 50 | 572 | 1143 |
| 2 | 47.5 | honeycomb 1.5 mm cells / spiral 1.0 mm gap | 40 / 30, 40, 50 | 572 | 1143 |
| 3 | 72.9 | spiral 1.0 mm gap | 30, 40, 50 | 572 | 1143 |
Mating features
Drawn at the exact size. Open press, slide, run and socket features by your process's clearance; leave designed gaps and clamp fits as drawn.
| feature | exact | mates with | fit | files |
|---|---|---|---|---|
| stack OD | spool bore (34.8 / 47.5 / 72.9) | tri-clamp spool bore | socket | stack-* |
Where the files are
Other publishers' files are linked, not hosted. "verify" = check the license at the link before commercial use.
| Wikipedia | Thermoacoustic heat engine | web | CC BY-SA 4.0 (text) |
| G. W. Swift (LANL) | Thermoacoustics: A Unifying Perspective for Some Engines and Refrigerators (textbook; DeltaEC software free) | web, software | LANL verify |
| NASA (NTRS, public domain) | Thermoacoustic Stirling heat engine for space power | US Government work, public domain | |
| Long Earth Society | Engine builds | web, video | LES site |
Free files
★ Free files 11 parts. Generated by Xem Studio from the standard; threads are plain cylinders at major diameter. CC BY 4.0. index.json
| stack-honeycomb-1.5in-40-c1.5 | honeycomb stack Ø34.8 × 40 (the 1.5 in spool bore, exact): 1.5 mm hexagonal cells, 0.4 mm walls | STEP · STL |
| stack-spiral-1.5in-30-g1.0 | spiral stack Ø34.8 × 30 (the 1.5 in spool bore, exact): one 0.4 mm wall wound with a 1.0 mm gas gap | STEP · STL |
| stack-spiral-1.5in-40-g1.0 | spiral stack Ø34.8 × 40 (the 1.5 in spool bore, exact): one 0.4 mm wall wound with a 1.0 mm gas gap | STEP · STL |
| stack-spiral-1.5in-50-g1.0 | spiral stack Ø34.8 × 50 (the 1.5 in spool bore, exact): one 0.4 mm wall wound with a 1.0 mm gas gap | STEP · STL |
| stack-honeycomb-2in-40-c1.5 | honeycomb stack Ø47.5 × 40 (the 2 in spool bore, exact): 1.5 mm hexagonal cells, 0.4 mm walls | STEP · STL |
| stack-spiral-2in-30-g1.0 | spiral stack Ø47.5 × 30 (the 2 in spool bore, exact): one 0.4 mm wall wound with a 1.0 mm gas gap | STEP · STL |
| stack-spiral-2in-40-g1.0 | spiral stack Ø47.5 × 40 (the 2 in spool bore, exact): one 0.4 mm wall wound with a 1.0 mm gas gap | STEP · STL |
| stack-spiral-2in-50-g1.0 | spiral stack Ø47.5 × 50 (the 2 in spool bore, exact): one 0.4 mm wall wound with a 1.0 mm gas gap | STEP · STL |
| stack-spiral-3in-30-g1.0 | spiral stack Ø72.9 × 30 (the 3 in spool bore, exact): one 0.4 mm wall wound with a 1.0 mm gas gap | STEP · STL |
| stack-spiral-3in-40-g1.0 | spiral stack Ø72.9 × 40 (the 3 in spool bore, exact): one 0.4 mm wall wound with a 1.0 mm gas gap | STEP · STL |
| stack-spiral-3in-50-g1.0 | spiral stack Ø72.9 × 50 (the 3 in spool bore, exact): one 0.4 mm wall wound with a 1.0 mm gas gap | STEP · STL |
Plain text: sheet.txt · JSON: /api/geometry?object=thermoacoustic-stack
How it fits
Goes in or on
Tri-clamp spool, 1.5 and 2 inchstack OD = spool boreConnects to
Thermoacoustic heat exchangers, hot and cold,…hot and cold exchangers on the stack faces
Thermoacoustic driver capspeaker cap closes the resonatorAlso needed
Tri-clamp end cap, 6 mm flatcapped hot end
Tri-clamp clamp, two-boltclamp per spool jointIn these build lists
Thermoacoustic standing-wave engine, 2 in spoolsNo moving parts: a heated stack between two heat exchangers in a closed-open 2 i…You might also need
Questions
What channel size should a thermoacoustic stack have?
2–4 thermal penetration depths: about 1–1.5 mm in air at 1 bar and 100–300 Hz.
How long should a thermoacoustic tube be?
Closed-open (λ/4): L = 343 / (4f): 286 mm for 300 Hz, 429 mm for 200 Hz, 858 mm for 100 Hz; closed-closed is twice that.
Where does the stack go?
Centred about λ/8 from the closed hot end: 107 mm in a 429 mm (200 Hz) λ/4 tube.
What diameter is the stack for a 2 inch spool?
Ø47.5, the 16 ga bore: a honeycomb stack × 40 or a spiral stack × 30, 40 or 50.