# Thermoacoustic hot-end fin sleeve: radial fins that slide over a 2 in closed-end cup

> How do I put fins on the hot end of a tri-clamp thermoacoustic engine?

- Category: Stirling engines › Thermoacoustic & fluidyne
- Kind: Hardware
- Basis: ASME BPE 2 in tube OD Ø50.8 (the sleeve's bore); fin count, thickness and reach are design values; M4 set screws ISO 4026
- Page: https://xemstudio.com/objects/thermoacoustic-hot-fin-sleeve/ · JSON: https://xemstudio.com/api/geometry?object=thermoacoustic-hot-fin-sleeve · Plain text: https://xemstudio.com/objects/thermoacoustic-hot-fin-sleeve/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.** 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.

## Notes

- A separate, optional heat exchanger for the closed hot end of the standing-wave engines: a sleeve whose bore is exactly the tube's Ø50.8 slides over the closed end of the plain cup-2in-133.35 (a standard closed-end 2 in spool, 133.35 mm), and 16 radial fins carry the torch's heat into the hot cavity and the hot exchanger. Three M4 set screws in a band above the fins hold it.
- It covers 49 to 131.85 mm from the cup's face, so it stays clear of the water jacket and the clamp; the fins reach Ø80, as far from the tube as the Ø76 fins the hot end used to carry built on.
- Without it the flame heats the bare cup: the engine is complete and still runs, but needs more heat to start. The cup stays a plain part a sanitary fabricator makes; the sleeve can be made any way you like.
- Fits: the bore slides on the tube OD (slide fit), the set screws clamp it.

## Mating features (exact size; open press / slide / run / socket by your process clearance, leave designed and clamp as drawn)

| feature | exact | mates with | fit | files |
|---|---|---|---|---|
| bore | Ø50.8 = the 2 in tube OD | cup-2in-133.35 tube OD (over its closed end) | slide | all |
| set-screw holes | 3 × Ø3.3 at 0 / 120 / 240° | M4 tap drill; M4 × 4 set screws onto the tube OD | clamp | all |
| fins | 16 × 1.6 to Ø80, 56–131.85 from the cup face | torch flame (no contact) | designed | all |

## Sizes

| feature | value |
|---|---|
| bore | Ø50.8 (tube OD) |
| length | 82.85 |
| wall | 2.0 |
| fins | 16 × 1.6 thick, to Ø80 |
| set screws | 3 × M4, 0 / 120 / 240° |
| fits | cup-2in-133.35 |

## Where the files are

- G. W. Swift (LANL / Acoustical Society of America): [Thermoacoustics: A Unifying Perspective for Some Engines and Refrigerators (Rott's equations, screen relations, DeltaEC)](https://www.lanl.gov/org/ddste/aldps/materials-physics-applications/condensed-matter-magnet-science/thermoacoustics/) — web, software — LANL (verify at link)
- Long Earth Society: [Engine builds](https://longearthsociety.com/engineering/) — web, video — LES site

## Free STEP/STL (1 parts, CC BY 4.0, Xem Studio)

Index: https://xemstudio.com/files/hardware/thermoacoustic-hot-fin-sleeve/index.json

- ta-fin-sleeve-2in-16x80: [STEP](https://xemstudio.com/files/hardware/thermoacoustic-hot-fin-sleeve/ta-fin-sleeve-2in-16x80.step) · [STL](https://xemstudio.com/files/hardware/thermoacoustic-hot-fin-sleeve/ta-fin-sleeve-2in-16x80.stl) — radial-fin sleeve for the 2 in tube: bore Ø50.8 (the tube OD) × 82.85, 2 mm wall, 16 radial fins 1.6 thick to Ø80 over the last 75.85, 7 mm band with 3 × M4 tapped (Ø3.3) at 0 / 120 / 240°; drawn in the cup's frame (49 to 131.85 from its face)

## Questions

**Do I need it?**

No. It is an optional heat exchanger; without it the engine needs more heat at the cup to start.

**Why not fins on the cup itself?**

Sanitary fabricators make plain spools and closed-end cups; fins built onto one are not something they make. A separate sleeve keeps the cup standard.

## Fits with

- [Tri-clamp cups: closed-end spools (ferrule on a capped tube), 1.5, 2 and 3 in](https://xemstudio.com/objects/tri-clamp-cups/)
- [Thermoacoustic stack for tri-clamp spools: Ø34.8, Ø47.5 and Ø72.9, honeycomb and spiral](https://xemstudio.com/objects/thermoacoustic-stack/)
- [Thermoacoustic heat exchangers, hot and cold, parallel plate, for 1.5, 2 and 3 in tri-clamp spools](https://xemstudio.com/objects/thermoacoustic-heat-exchanger/)
- [Thermoacoustic bore spacers and liners for 2 in tri-clamp spools: 8.4, 60 and 61.7 mm](https://xemstudio.com/objects/thermoacoustic-bore-spacer/)
- [Thermoacoustic water jacket: 14 mm clamp-on halves for a 2 in tri-clamp tube](https://xemstudio.com/objects/thermoacoustic-water-jacket/)
- [Set screws (grub screws), M3–M8 (ISO 4026)](https://xemstudio.com/objects/set-screws-metric/)
- [Build list: Thermoacoustic standing-wave engine, quarter-wave, propane, 2 in tri-clamp](https://xemstudio.com/objects/list-ta-standing-quarter-wave-2in/)