# Thermoacoustic jet pump: 2 in, Ø20 to Ø8 taper

> How do I stop the steady flow round a looped thermoacoustic engine?

- Category: Stirling engines › Thermoacoustic & fluidyne
- Kind: Hardware
- Basis: Backhaus & Swift's jet pump: an asymmetric orifice whose minor-loss difference between the two flow directions sets a steady pressure drop that opposes Gedeon streaming
- Page: https://xemstudio.com/objects/thermoacoustic-jet-pump/ · JSON: https://xemstudio.com/api/geometry?object=thermoacoustic-jet-pump · Plain text: https://xemstudio.com/objects/thermoacoustic-jet-pump/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 torus lets the gas drift steadily round the loop (Gedeon streaming), carrying heat from the hot exchanger straight to the ambient one. A tapered hole loses more pressure on the flow out of its small end than into it, so it sets a steady pressure difference that can cancel the drift: Backhaus & Swift's jet pump.
- Here a Ø47.5 plug, 30 long, sits in the junction cross's lower branch on the gasket lip, its taper from Ø20 (junction) to Ø8 (the ¾ in inertance line). The linear model counts it as a duct of the mean bore.
- Only the twin-piston engine needs it: in the ring engine the pistons themselves block the loop.

## 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 |
|---|---|---|---|---|
| outside | Ø47.5 | 2 in cross branch bore | slide | all |
| taper | Ø20 → Ø8 over 30 | oscillating gas (no contact) | designed | all |

## Sizes

| feature | value |
|---|---|
| outside | Ø47.5 |
| taper | Ø20 → Ø8 |
| length | 30 |

## Where the files are

- 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)
- 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-jet-pump/index.json

- jet-pump-2in-30: [STEP](https://xemstudio.com/files/hardware/thermoacoustic-jet-pump/jet-pump-2in-30.step) · [STL](https://xemstudio.com/files/hardware/thermoacoustic-jet-pump/jet-pump-2in-30.stl) — jet pump Ø47.5 × 30: conical bore Ø20 at the junction side to Ø8 at the inertance side

## Questions

**Why not a membrane?**

A membrane works too but has to survive the stroke; the jet pump has no moving part.

## Fits with

- [Build list: Thermoacoustic-Stirling engine with twin free-piston alternators, 2 in, pressurised](https://xemstudio.com/objects/list-ta-twin-piston-2in/)
- [Thermoacoustic buffer-tube liner: 2 in, 0.5 wall, 180 and 140 mm](https://xemstudio.com/objects/thermoacoustic-buffer-tube-liner/)