Didn't Cray submerge the circuit boards in liquid freon? IBM did some heroic cooling too.
My pulser will mount deep inside the customer's gadget, and he does have a cold water system. I just need to figure out the best way to insulate the fet drain but suck the heat out. We have tools to simulate circuits, but not thermal systems. Electronic circuits have nice equipotential nodes on a planar schematic; thermal systems are
3D, distributed, diffusive, and in this case involve liquid flow. The component thermal specs aren't to be trusted either; you can thank IR for that.Water is fabulous thermally, but it's awful electrically. The dielectric constant is huge.