[bobo5195]

The idea of using extra fins is a good one and I especially like the long detailed write up as it makes my brain hurt so much less.

Given your unlimited machining budget I would say it is a fairly good design. I don’t expect performance to be right up there as the fins are very thick (due to the horizontal fins). This means that the vertical fins have to be thicker and overall heat transfer area is less. Could be an interesting exercise to compare thermal transfer per unit area to something like the apogee. It may be slightly lower as the horizontal fins stop hotter water from displacing from the surface. I know this will be a small effect but it could account for a lot. There was a paper I read which tried to determine if heat transfer rate could be increased by machining 1mm wide grooves to increase surface roughness. That is another approach that could be useful.

The few little things I would change without going to something completely different

I disagree with the flow splitting approach as it half’s your mass flow rate for no reasons.
Increase the number of fins if possible.
Remove the small vertical fin at the base as it kills machinability.
Forget drilling holes in the top of the small vertical fins. It reduces performance as the water in those holes is going nowhere (just getting hot and naturally convecting) and adds extra pressure drop across the device.
The holes in the side reduce the performance as the water goes through these instead of around a nice long path in the block.

Happy building. Extended fins like these are one good approach and with tweaking maybe able to generate a quite high level of performance.

I was born in that area of Africa so I to have heard of bushman tech quite a lot .