Interesting concept - i've wondered before if it would be possible to make a phase change system with water.
It would be cool if you could make a diagram of your system so we can see how you picture it.
The problems I had when trying to determine if it's possible or not -
-how do you produce a flow rate in the system? you mention no compression, but you're in a vacuum, so how do you get your 'refrigerant' to cycle
-water has great heat transfer capabilities so this type of system could probably produce a great btu/hr but in the end your operating temp is still 120-130f isn't it? Your cycle won't even start until your cpu or whatever heat sources you have bring your refrigerant up to that temp which is around 50c - a temp that i would feel is uncomfortably warm for my system. My phase change system is in pieces right now but with just my watercooling setup with a fan blowing over the res (in place of evaporator submerged in res) i'm at 87f (31c) under full load
-implications of pure water in the system - corrosion, lubrication of moving parts / pump / compressor, etc
It's an intriguing idea and i'd do it too if i could figure out how to make it work - new and unusual = fun project
It seems like this type of concept would only really be suited for cooling something where the 120-130 operating temp is appropriate to what's being cooled
once i saw an old ammonia based air conditioner from the 40's - it had a gas fired burner in it and pumped chilled ethylene glycol into the house, i don't have clue how it worked but whatever principle it used might be useful here! anyone here know anything about that type of system?