# Water tray for a 10 in cold cap (optional)

> How do I cool the top of a big flat Stirling engine?

- Category: Stirling engines › Tri-clamp engine parts
- Kind: Hardware
- Basis: Exact geometry
- Page: https://xemstudio.com/objects/htd-water-tray-10in/ · JSON: https://xemstudio.com/api/geometry?object=htd-water-tray-10in · Plain text: https://xemstudio.com/objects/htd-water-tray-10in/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 heat exchanger, optional: an open ring tray that sits on the cold cap's flat top round the 2 in ferrule and holds water. The cap takes about the cup wall's leak plus the engine's rejected heat (a few hundred watts at full fire), so the water warms and has to be topped up; ice water helps. The engine runs without it, hotter on the cold side.

## 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 |
|---|---|---|---|---|
| floor | Ø118–Ø190 | cold cap flat top (sits on it) | designed | all |
| ID | Ø118 | 2 in ferrule, clamp and gauge boss (no contact) | designed | all |

## Sizes

| id_mm | od_mm | height_mm |
|---|---|---|
| 118.0 | 190.0 | 40.0 |

## Where the files are

- 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/htd-water-tray-10in/index.json

- water-tray-10in: [STEP](https://xemstudio.com/files/hardware/htd-water-tray-10in/water-tray-10in.step) · [STL](https://xemstudio.com/files/hardware/htd-water-tray-10in/water-tray-10in.stl) — water tray (heat exchanger, optional): ring Ø118/Ø190 × 40, 2 walls and floor, sits on the cap's flat top

## Questions

**Does the engine need the tray?**

No, but the cold side runs hotter and the output drops without it.

## Fits with

- [Build list: HTD engine, 10 in tri-clamp (high-temperature-differential flat engine)](https://xemstudio.com/objects/list-htd-10in/)
- [HTD cold caps: 10 in tri-clamp caps with a 2 in ferrule at the centre](https://xemstudio.com/objects/htd-cold-caps-10in/)