Wired magazine has published a Sony video showing a teardown of a Playstation 4. To me the internal mechanical design is almost identical to the PS3, with one centrifugal fan. The only thing different is the integration: one chip instead of a separate graphics chip in the PS3.
I thought it was interesting Sony did the teardown, I don't remember them doing that before.
http://www.wired.com/gamelife/2013/11/playstation4-teardown-video/