I was working on a so called finless cooler around the time this first rose to prominence. The idea was that a toroidal vortex would give better heat transfer t

I was working on a so called finless cooler around the time this first rose to prominence. The idea was that a toroidal vortex would give better heat transfer than a lot of fins subject to viscous shear. Our cooler was simply a folded aluminium sheet with a fan placed into a hole in the top. We had a somewhat similar couette type flow under our motor hub directly over the heat source. We had a modest 15% gain over a reference GPU cooler which was almost entirely due to the better thermal conductivity of the aluminium sheet over the cast heat sink in the reference design. It turned out that all that matters is cost, nothing else.