Ok back a lifetime ago I worked with ammonia filled heat pipes on a satellite that used capillary action to return the fluid back to the "hot" portion of the "payload"
I've heard that most if not all of the heat pipes on PC are very simple and only rely on gravity to sustain the thermodynamic cycle.
That leads me to my question: Is there an optimal mouting orientation (sts) for heat sinks with heat pipes on a PC?
Just by looking at most of them, it seems they are designed to work best with the CPU at the bottom and the heat pipes oriented vertically from there. Thus I would conclude that with a tower case that most heat pipe style HSF's would work best if the tower were laid on it's side (sts).
I believe the heat transfer on most of these pipes are more dependant on the phase change reaction as the cpu heat turns most likely ammonia liquid into a gas at a higher pressure that facilitates the carrying of heat away from the cpu. The return mechanism is a wick of sort that fibers expand to draw fluid by fibrous expansion and absorbsion.Also thermo-dynamically it's a fluid dynamic system, which like currents and convection models, are rarely affected by gravity especially when pressurized.