Re: Noisy fans
You would indeed need to replace it periodically. But I need to replace the water in the water dispenser in my fridge periodically. It's not that onerous.
If I were designing a liquid cooling system for e.g. something that had to be somewhere sensitive, then there would be a number of things I'd do. I'd limit the inventory of cooling fluid to minimise the consequences if it leaked. I might use something like glycol to give me a lower freezing point. I'd run it through tiny labyrinthine pipes and circulate it to maximise transfer, and when the hot side got back to the reservoir, I'd actively cool it with some kind of refrigerant setup, because with limited inventory you'd need to shed the heat to the air quickly before reusing it. I've more or less described a domestic fridge, there.
BUT...
If I were designing a cooling setup for something I'm just using casually at home, my model would not be the fridge, it would be the sink full of ice water I use to cool beer cans.
For device cooling, step one is make the device heat sink long enough (150mm?) and heat conductive enough that the device and sit on one side of a reservoir lid and dip through it into the cooling medium, which is just tapwater, with optional ice. With an essentially unlimited inventory (a five litre tank wouldn't be terribly inconvenient to have on your desk) there's a HUGE capacity for absorbing heat there. Little tap on it to drain it off when it's hot, funnel at the opposite corner for topping it up from a jug, largish lidded opening for adding ice-cubes. You might top it up once a day? Convection alone would probably be enough but if not a tiny stirrer just to get the water moving would do. Little cheap instrument sitting on top to alert you if the temp gets too high. Can't see the whole setup costing more than £50 retail. That said, can't see many domestic customers for it either - it's slightly more faff than just switching your PC on and going, and slightly more faff = no interest, I suspect.
I lack the expertise to know if anyone cares enough about cooling Pi's and similar to make something like this interesting enough to produce. Anyone?