I've seen water-cooled tape drives that were plumbed with plastic tubing, and they never leaked as far as I know.
I was in the new Data Center of a large bank last year, and they used chilled water piped to each individual rack. The racks were sealed and had their own air circulation system with a small "radiator" for the water to flow through.) The water flowed through plastic tubing to and from the racks, as well as inside the racks.
One of the first computers I worked on came out of a Polaris missile. We used it in our physics lab to control experiment processes. It was all discrete parts (no ICs), analog, and required liquid cooling in the missile. It had a bunch of copper tubing that ran in-between the cards. They started out just putting a fan on it for our application (working in air instead of a vacuum minimized the cooling issues). But the pipes were left in place, and without the bulkheads from the rest of the missile, they were pretty much unsupported. When the fan ran, they vibrated around. Eventually, they pounded through the conformal coating and shorted something out, POOF, magic smoke released. The desk I inherited was absolutely full of TO-5 case transistors either taken out of it after blowing, or new ones to be used when the others blew. Hundreds of them.
When I got into a real job, we used the liquid-cooled Cray 2 as our primary simulation platform. We started out renting time on them, but eventually we got several of our own. Eventually we sold them to the Air Force, and they ended up at Schriever AFB in the National Test Facility for the Strategic Defense initiative. They became obsolete, but the particular machine I preferred sat in the lobby with its 'waterfall" cooling array still running for decorative purposes, until pretty recently
Brett
