About sandblasted surface: i've been thinking about that for a long time... I think that there's a limit under which surface features act by 'stopping' water molecules, and not 'throwing them around' as a bigger feature does.
I think there's a limit dictated by water viscosity, or surface tension, or both. Under this limit, surface features would only thicken the boundary layer, thus reducing the heat transfer.
(personal experience): in ultra-vacuum chambers one heats the chamber walls to make them reject water & gases molecules trapped by adsorption. (Try a google on 'adsorption' to know what it's about). Because any surface is not perfect, its surface features would trap other materials molecules that come into contact.
I tend to link that 'trapping' effect to the boundary layer between a solid and a fluid in motion. Maybe i'm wrong, it's just pure speculation.
If i'm right, then mirror finished waterblock transfer surfaces would perform better than sandblasted (or rough) ones.
The limit in surface feature size would be in accordance to the minimum radius of a water drop against that surface. Does that make sense ?
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