equivalent to a HP Z cooler?

[pocock]

Is there any possibility of somebody marketing a fanless POWER9 cooler similar to the HP Z coolers?

Maybe this would not be feasible for the 22 core chips but it would be very interesting for 4-core.  Not only is it silent but it also eliminates one possible type of mechanical failure.

[ClassicHasClass]

There's the 2U heatsinks. I use one in a Blackbird. Works well enough but I would only use it for the 4-core.

[Borley]

There's the 2U heatsinks. I use one in a Blackbird. Works well enough but I would only use it for the 4-core.

You have air moving across it in some capacity though? No issues with throttling or anything?

[pocock]

The HP Z cooler is not simply fanless, it is based on 3D vapor chamber phase-change cooling with staggered hex-fin heat exchangers

HP published some research about this technology

[ClassicHasClass]

There's the 2U heatsinks. I use one in a Blackbird. Works well enough but I would only use it for the 4-core.

You have air moving across it in some capacity though? No issues with throttling or anything?

Yes, there are case fans. It's never gotten into overheat territory since those were installed.