- May 1, 2017
The thermal gradient in the fluid will definitely be affected by channel diameter, but the convective heat transfer coefficient is also a product of flow rate and surface area. Larger tubes will have more contact area and less flow restriction with generally drives the convection coefficient up for the same pressure head. The length will be reduced slightly by the allowable radius of curvature for the bends at the larger diameter; unless of course the tube is so "wide" that you have fewer channel runs, so there will be a trade there.As I understand it, the issue has more to do with the proportion of liquid in the tube that is in close proximity to the walls of the copper (for more efficient heat transfer). The total tube length is typically also reduced if I remember right (which I definitely may not). That will contribute to less restriction, which would be great if you're limited by a weaker pump, but will hurt performance if you're not. Further back in the thread, Wahaha360 ran into this very issue while testing custom radiators.