I like the design, but I would suggest making the pin area larger. You got a nice big chunk of copper there, but you're only using about 1/3 of the block for metal to water transfer. BUt all in all that design is gonna make a hell of a lot of turbulance, which is a good thing. Also, if its physically possible, try increasing the surface are of the pins by putting little indents on the pins, doing something like this pic, it would make it look cooler too.