Characterization of the Effect of Surface Roughness and Texture on Fluid Flow: Past, Present and Future

That surface roughness has an effect on fluid flow in networks has been understood for well over a century. The exact effect roughness has on fluid flow has not been completely understood, but a working estimate has been offered by a variety of authors over time. The work of Colebrook, Nikuradse, and Moody has provided practitioners with a method to include at least a first order estimate of roughness effects, but their work has been limited to relative roughness to diameter values of 5% or less. Modern fluidic systems at the mini and micro levels routinely violate the 5% relative roughness threshold due to the inability to control the roughness of surfaces to sufficient levels with respect to decreasing system scale. Current work by Kandlikar, et al., has extended the traditional methods of assessing surface roughness effects up to 14% relative roughness by including the effect of constricted flow diameters and modifying the Moody diagram to reflect new experimental data. The future of micro fluidics would suggest that trends for miniaturization will continue and that further understanding and experimentation will be warranted. This is especially true with regards to understanding the role of roughness on the flow in mini and micro channels.