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Free-piston internal fin inserts: slotted heater and cooler sleeves for a 2 in tri-clamp bore (optional)
Do I need internal fins in a tri-clamp Stirling heater and cooler? · Hardware · basis: Design values of the free-piston generator: 36 axial slots 1.5 × 2.5 in a sleeve whose OD is the 2 in bore (Ø47.5); heat-transfer and flow numbers from the generator's simple analysis
Long Earth Society build part. Optional fin inserts for my free-piston generator. 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
- 2 in table
Notes
- Two slotted sleeves that slide into the plain tri-clamp parts: the heater insert on the liner's lower end inside the closed-end spool, the cooler insert pressed into the 3 in spool under the water jacket. The gas runs along the 36 slots, between fins that touch the wall.
- Optional: without them the heater is the plain 3.0 mm annulus round the liner and the cooler the 4.05 mm annulus round the displacer. The engine still runs; my analysis gives 6.6 W instead of 43.2 W at the same stroke (helium, 10 bar), because the gas-side heat transfer falls and the cooler annulus adds dead volume.
- Fits: the heater insert slides on the liner (press) and its OD against the hot spool's bore (slide); the cooler insert's OD is pressed into S3, its Ø40 bore is the displacer's 0.30 gap.
Sizes
| insert | id_mm | od_mm | length_mm | slots | slot_mm |
|---|---|---|---|---|---|
| heater | 41.5 | 47.5 | 68.05 | 36 | 1.5 × 2.5 |
| cooler | 40.0 | 47.5 | 73.2 | 36 | 1.5 × 2.5 |
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 |
|---|---|---|---|---|
| bore | Ø41.5 | liner tube OD | press | fpse-heater-insert* |
| OD | Ø47.5 | hot spool bore (hot wall) | slide | fpse-heater-insert* |
| OD | Ø47.5 | S3 spool bore | press | fpse-cooler-insert* |
| bore | Ø40.00 | displacer Ø39.4 (0.30 radial gap, no contact) | designed | fpse-cooler-insert* |
| slots | 36 × 1.5 wide × 2.5 deep | gas passages (no contact) | designed | all |
Where the files are
Other publishers' files are linked, not hosted. "verify" = check the license at the link before commercial use.
| Ohio University (Urieli) | Stirling cycle machine analysis: ideal adiabatic and simple analysis (after Urieli & Berchowitz, Stirling Cycle Engine Analysis, 1984) | web | author's site |
| Long Earth Society | Engine builds | web, video | LES site |
Free files
★ Free files 2 parts. Generated by Xem Studio from the standard; threads are plain cylinders at major diameter. CC BY 4.0. index.json
| fpse-heater-insert-41.5x47.5 | heater insert (optional): Ø41.5 / Ø47.5 × 68.05, 36 slots 1.5 × 2.5 deep in the OD, full length; on the liner's lower end, OD against the hot wall | STEP · STL |
| fpse-cooler-insert-40x47.5 | cooler insert (optional): Ø40 / Ø47.5 × 73.2, 36 slots 1.5 × 2.5 deep in the OD; pressed into the 3 in spool S3, its bore continues the displacer's bore | STEP · STL |
Plain text: sheet.txt · JSON: /api/geometry?object=fpse-fin-inserts
How it fits
In these build lists
Free-piston Stirling generator, 2 in tri-clamp…A real free-piston Stirling generator in standard 2 in sanitary fittings: closed…You might also need
Questions
What if I leave them out?
The engine is complete without them; expect about 6.6 W instead of 43.2 W at 10 bar helium.