@esa_aardvark,
Engine 10 cylinder 100000hp diesel. I am sure that you
could cool down the diesel exhaust somehow, intercoolers?
Given the impressive efficiencies (they come within a nat's whisker of the theoretical 50% limit) that are achieved by the modern large ship diesel engines, there's nothing left in the exhaust to recover after the turbo chargers and whatever other tricks they employ. They even go as far as to use the air compressed under a descending piston to push up the adjacent one on its up stroke.
Would it be better to go back to such low tech that actually works.
At the expense of fuel efficiency, yes. The good old Olympus has about the same power output, ish, will work for 1,000,000 years but will drink more fuel. And Olympus is a much better name than WR21, or Trent, or whatever.
Diesels aren't as useful in a warship - slow to respond to the telegraph, and they're the wrong shape (tall) and take up a lot of space. A 100,000 HP diesel in a 130,000 ton freighter is, comparatively speaking, just a small unit at the back of the ship. The same engine in a 8,000 destroyer would pretty much mean that there's nothing else on the ship!
As for not liking running in hot water - the Persian Gulf gets pretty warm, as any submariner who has served out there (plus any submarine equipment designer) will tell you. I'm told that the ambient internal air temperature on T boats whilst submerged in the Persian Gulf during the summer was in the order of 50 deg C. Hot. Submarines there are big black rubber coated things basking in warm shallow waters under a scorching sun, and the T's air con plants were designed for the North Atlantic... Now imagine living and working in that for 2 weeks with no shower... yeurk! Round of applause for our submerged friends I think.
No one should be surprised that the Gulf sea water gets hot. RR are the design authority for literally every RN engine working out there, so they surely know (not they they built the recuperator). No doubt that somewhere within the inbox of a variously inhabited designation in Abbey Wood is a concerned email from people who know to people who need to know, but weren't there long enough to be able (or be obliged) to do anything about it.