how does a portable air conditioner work (one that consumes water)

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Many years ago my parents had some kind of portable air conditioner:
It is a noisy thing on casters with a water tank that you have to refill every day,
it inhales warm air from the room, expels cool dry air back into the room, and also expels hot moist air outside through an exhaust pipe that fits on a window.

How does it work?

I suppose that the water evaporation generates some cooling, I would expect it to create just a bit of cool moist air rather than a stream of cool dry air...