Random Nonsense said:
trust me on it 
i know a fair bit about this stuff because im learning a lot about aerodynamics at college.... air is a fluid, behaves like water.... boundary layer is a factor, not a huge one but turbulance will give u maybe a degree or 2 better performance.
proof of what i said: the tubing restricts flow. Why is this? the friction between the water molecules and the walls of the tubing!
it is like using lots of small tubes in a radiator than one huge pipe! the water in the middle is not picking up as much heat as the water close to the surface.... introducing turbulence lets this water take heat from the surface, therefore more cooling!
william and random nonsense are on the money
when a fluid moves across a non moving surface, there is a point where the fluid comes into contact with that surface. (obviously). we'll call the surface the Block.
when that happens, the surface of the liquid reacts against the friction of the Block where they contact one another and the motion on the surface of the liquid slows down or stops at that contact point. this is called the boundry layer.
as we know, moving liquid across a surface is what provides us the best heat transfer abilities. when that liquid stops, it's doing a less efficient job. the liquid of the boundry layer is relying on normal convection to warm it up enough so it rises off the contact surface and back into the waterflow. at which point it's replaced with something cooler when it leaves.
creating a small amount of turbulence on the contact surface of the block will prevent the boundry layer from forming and increase the Heat Transfer potential of your apparatus.
due to the size of our systems, this performance increase is marginal at best, but it's there. and we all know that its the little things all added up in the end that give us the performance we're looking for.
William was right. randomly soddered little 'nubbs' along the surface of the copper would work and create enough turbulence to prevent the boundry layer from forming - so would small perpendicular grooves (as in a unfinished piece of copper, or taking a file to the surface of it). where this becomes a factor in a tube, they generally fasten a small wire or spring inside the length of the tube to which breaks up the boundry layer and helps maintain a little surface turbulence. on another note, this technique might also help you guys with radiator problems looking to grab another couple of degrees of cooling power from it. i haven't tested it, but in theory it should be a decent idea.
ifmu - your idea isn't without merit but i believe is overkill if the only purpose is to create turbulence inside your block. there are alot of parts that need to be kept in optimal working order, which would require a certain amount of maintenance. theres also the issue of reduced flow rates due to the resistance of your rotating "piston".
keep crankin mr man. nice to see original ideas up here.
