# Build list: Thermoacoustic-Stirling engine with twin free-piston alternators, 2 in, pressurised

> What parts do I need to build a Thermoacoustic-Stirling engine with twin free-piston alternators, 2 in, pressurised?

- Category: Stirling engines › Assembled engines
- Kind: List / guide
- Basis: Every part is a free STEP/STL on this site or a standard part with its own page; quantities are the full count, every screw, nut, gasket and clamp. Numbers from the linear network model in tools/gen_ta_power.py (Rott / Swift equations, written from the published method).
- Page: https://xemstudio.com/objects/list-ta-twin-piston-2in/ · JSON: https://xemstudio.com/api/geometry?object=list-ta-twin-piston-2in · Plain text: https://xemstudio.com/objects/list-ta-twin-piston-2in/sheet.txt
- License: dimension sheet CC BY 4.0 (Xem Studio); linked files under their publishers' licenses
- Use in every chat: add https://xemstudio.com/mcp as a connector (https://xemstudio.com/use-with-ai/)

**Exact dimensions.** True size, with no printing tolerance added.

## Notes

- Backhaus & Swift's thermoacoustic-Stirling torus in 2 in tri-clamp with two opposed free-piston alternators on the junction cross, a jet pump, helium charge and a torch drum.
- Numbers: 20 bar helium · 24 Hz · onset 204 °C with the alternators open · ≈ 9 W electric for ≈ 67 W into the hot exchanger (14 %) at ±8 mm (model)

## Sizes

| subsystem | object | parts | qty | note |
|---|---|---|---|---|
| None | tri-clamp-custom-length-spools | spool-2in-310.7mm | 1 | core: plain 2 in tube with full ferrules |
| None | thermoacoustic-bore-spacer | ta-spacer-2in-8.4 | 2 | gasket lip to each ambient exchanger |
| None | thermoacoustic-slotted-exchanger-insert | hx-insert-2in-14 | 2 | main ambient (top) and secondary ambient (bottom) exchanger |
| None | regenerator-screen-disc-47-5 | screen-disc-47.5-m100 | 550 | regenerator: 110 mm of 100-mesh × 0.10 screen |
| None | thermoacoustic-slotted-exchanger-insert | hx-insert-2in-12 | 1 | hot exchanger |
| None | thermoacoustic-buffer-tube-liner | tbt-liner-2in-140 | 1 | thermal buffer tube |
| None | sanitary-clamp-crosses | cross-2in | 1 | the junction: core up, inertance down, a piston each side |
| None | thermoacoustic-jet-pump | jet-pump-2in-30 | 1 | in the cross's lower branch, on the gasket lip: stops the steady flow round the torus |
| None | tri-clamp-caps-with-welded-boss | cap-2in-x-0.75in-ferrule | 2 | top of the core and bottom of the cross: the ¾ in inertance line joins here |
| None | tri-clamp-honed-cylinder-spool | spool-2in-6in-honed-48.00 | 2 | piston cylinders, either side of the cross |
| None | free-piston-mover-2in | mover-core-2in-130 | 2 |  |
| None | free-piston-mover-2in | mover-sleeve-48x130 | 2 |  |
| None | neodymium-block-magnets | magnet-block-30x10x4 | 96 | 48 per mover |
| None | canned-linear-alternator-stator-2in | stator-bobbin-half-2in-112 | 4 |  |
| None | canned-linear-alternator-stator-2in | stator-coil-2in-14x7 | 8 |  |
| None | canned-linear-alternator-stator-2in | stator-iron-half-2in-112 | 4 |  |
| None | socket-head-cap-screws-metric | shcs-m4x16 | 14 | return-shell ears (12), fin-sleeve ears (2, optional) |
| None | tri-clamp-flexure-carrier | flexure-carrier-2in-60 | 2 | outboard of each cylinder |
| None | spiral-flexure-bearing | flexure-40-3arm-w1.6-t0.5 | 8 | two per stack, opposite spiral hand |
| None | flexure-stack-spacer | spacer-40-t2 | 4 |  |
| None | flexure-rim-clamp-plate | clamp-plate-40 | 4 |  |
| None | flexure-hub-clamp-washer | hub-clamp-40-b4 | 4 |  |
| None | socket-head-cap-screws-metric | shcs-m3x10 | 12 | stack rims into the carrier ledges |
| None | threaded-rods-metric | rod-m4x195.9 | 2 |  |
| None | hex-nuts-metric | nut-m4 | 33 | hub nuts (8), return-shell ears (12), drum tabs (3), hangers (4), jackets (4, optional), fin sleeve (2, optional) |
| None | flat-washers-metric | washer-m4 | 8 | under each hub nut |
| None | tri-clamp-spool | tc-spool-2in-12in | 2 | bounce spaces outboard of the carriers |
| None | tri-clamp-end-cap | tc-cap-2in-flat | 2 | close the bounce spools |
| None | tri-clamp-gasket | tc-gasket-2in | 11 | Type B profile at every 2 in joint, rated above the relief setting at the joint's temperature |
| None | sanitary-clamp-elbows | elbow-90-0.75in | 4 |  |
| None | sanitary-clamp-spools | spool-0.75in-12in | 2 | bottom and top runs |
| None | sanitary-clamp-spools | spool-0.75in-3in | 1 | riser, lowest spool |
| None | sanitary-clamp-spools | spool-0.75in-6in | 1 | riser, top spool |
| None | tri-clamp-custom-length-spools | spool-0.75in-80.4mm | 1 | riser between the tee and the cross |
| None | sanitary-clamp-tees | tee-0.75in | 1 | fill branch |
| None | sanitary-clamp-crosses | cross-0.75in | 1 | gauge and relief branches |
| None | tri-clamp-caps-with-welded-boss | cap-0.75in-x-1-4npt | 3 | close the branches; each carries a 1/4 NPT instrument |
| None | npt-thread-envelopes | npt-1-4-male | 3 | 1/4 NPT stems of the fill valve, pressure gauge and relief valve |
| None | sanitary-clamp-gaskets | gasket-0.75in | 15 | Type B profile at every ¾ in joint |
| None | thermoacoustic-burner-drum | drum-single-lower | 1 | round the hot zone; flue to the front, down to the torch |
| None | thermoacoustic-burner-drum | drum-single-upper | 1 |  |
| None | socket-head-cap-screws-metric | shcs-m4x20 | 7 | drum tabs (3), hangers (2 per hanger) |
| None | tri-clamp-torch-stand | torch-stand-40 | 1 | on the bench under the flue; propane / butane torch head in its ring |
| None | set-screws-metric | set-m4x10 | 3 | centre the torch head |
| None | thermoacoustic-water-jacket | ta-jacket-half-2in-14 | 4 | optional: over the two ambient exchangers |
| None | socket-head-cap-screws-metric | shcs-m4x25 | 4 | optional: jacket ears |
| None | thermoacoustic-fin-sleeve | fin-sleeve-half-2in-34 | 2 | optional: over the hot exchanger inside the drum |
| None | tube-hanger-post | hanger-post-2in-h235.3 | 2 | under the bounce spools: the engine stands on these two posts |
| None | spool-hanger-collars | hanger-2in-tab | 2 | round the bounce spools, bars to the posts |
| None | spool-hanger-collars | hanger-2in-plain | 2 |  |
| None | socket-head-cap-screws-metric | shcs-m5x16 | 4 | hanger bars into the posts' tapped holes |

## Where the files are

- Nature (S. Backhaus, G. W. Swift): [A thermoacoustic Stirling heat engine, Nature 399, 335-338 (1999)](https://doi.org/10.1038/20624) — web — journal article; cited (verify at link)
- J. Acoust. Soc. Am. (S. Backhaus, G. W. Swift): [A thermoacoustic-Stirling heat engine: detailed study, JASA 107(6), 3148 (2000): torus with inertance and compliance, thermal buffer tube, jet pump against Gedeon streaming](https://doi.org/10.1121/1.429343) — web — journal article; cited (verify at link)
- Appl. Phys. Lett. (S. Backhaus, E. Tward, M. Petach): [Traveling-wave thermoacoustic electric generator, APL 85, 1085 (2004): a thermoacoustic-Stirling engine driving linear alternators, 18 % heat to electricity](https://doi.org/10.1063/1.1781739) — web — journal article; cited (verify at link)
- Applied Energy (Z. Wu, G. Yu, L. Zhang, W. Dai, E. Luo): [Development of a 3 kW double-acting thermoacoustic Stirling electric generator, 136, 866-872 (2014): three engines and three linear alternators in a loop, 5 MPa helium, 86 Hz, 1.57 kW electric, 16.8 %](https://doi.org/10.1016/j.apenergy.2014.04.105) — web — journal article; cited (verify at link)
- G. W. Swift (Acoustical Society of America / LANL): [Thermoacoustics: A Unifying Perspective for Some Engines and Refrigerators (Rott's equations, the energy equation, screen relations; the method behind DeltaEC)](https://www.lanl.gov/org/ddste/aldps/materials-physics-applications/condensed-matter-magnet-science/thermoacoustics/) — web, book — cited (verify at link)
- J. Thermophysics and Heat Transfer (G. W. Swift, W. C. Ward): [Simple harmonic analysis of regenerators, 10(4), 652-662 (1996): stacked-screen friction c1(φ) = 1268 − 3545φ + 2544φ²](https://doi.org/10.2514/3.842) — web — journal article; cited (verify at link)
- Steel & O'Brien: [Clamp ratings (clamp + elastomer gasket assembly): 2 in single-pin 450 psi at 70 °F / 300 psi at 250 °F; high-pressure bolted 1000 / 800 psi](https://www.steelobrien.com/wp-content/uploads/2020/06/SOB-Clamp-Ratings.pdf) — PDF — manufacturer's rating sheet; numbers cited
- NIST Chemistry WebBook: [Thermophysical properties of fluid systems (helium, air): viscosity and conductivity used for the model's fits](https://webbook.nist.gov/chemistry/fluid/) — web — US Government data
- Long Earth Society: [Engine builds](https://longearthsociety.com/engineering/) — web, video — LES site

## Build order

1. Posts on the bench under the two bounce spools: the whole engine stands on them, the core upright on the cross.
2. Core as on the ring engine (550 screen discs, 140 liner); 2 in cap with the ¾ in ferrule on top; the core on the cross.
3. Jet pump into the cross's lower branch, small end down, on the gasket lip; 2 in cap with the ¾ in ferrule under it.
4. Two power modules as on the ring engine, horizontal, one each side of the cross; 12 in bounce spool and flat cap outboard of each carrier; hangers round the bounce spools bolted to the posts.
5. Drum round the hot zone, flue to the front over the torch stand; ¾ in line from under the cross round to the top cap with the fill tee and the gauge-and-relief cross; jackets (optional); charge, leak-check, load connected before lighting.

All printed STLs: https://xemstudio.com/objects/list-ta-twin-piston-2in/stl-list.txt

## Questions

**How much electricity does it make?**

About 9 W in the model at 20 bar helium and 550 °C.

**Does it run in air or at 1 bar?**

Not at a torch's temperature in my model: this layout needs pressurised helium.

**Why two pistons?**

Twice the piston area at the junction, and opposed so the engine does not shake.

## Fits with

- [Build list: Thermoacoustic-Stirling ring generator, three 2 in units, pressurised](https://xemstudio.com/objects/list-ta-ring-3x2in/)
- [Thermoacoustic jet pump: 2 in, Ø20 to Ø8 taper](https://xemstudio.com/objects/thermoacoustic-jet-pump/)
- [Free-piston mover for a 2 in honed spool: piston and alternator magnets in one, Ø48.00 × 130](https://xemstudio.com/objects/free-piston-mover-2in/)
- [Linear-alternator stator that clamps round a 2 in tri-clamp tube: four coils outside the pressure wall](https://xemstudio.com/objects/canned-linear-alternator-stator-2in/)
- [Hanger post: holds a spool hanger round a horizontal 2 in tube](https://xemstudio.com/objects/tube-hanger-post/)
- [Build list: Thermoacoustic traveling-wave loop, 2 in tri-clamp](https://xemstudio.com/objects/list-ta-loop-2in/)