Numerical Analysis of Roughness Effect on Fluid Flow in a Micro Tube with a Three-Dimensional Roughness Element Model

Though predicted by the Moody chart that if lower than 5%, the effect of roughness on laminar flow characteristics can be ignored in macro-scale tubes, the statement is challenged by the recent experimental studies for fluid flow in micro-scale tubes. In this paper, a simplified three-dimensional roughness element model was constructed based on the SEM observation of the inner wall topography of a stainless microtube. Numerical calculations were carried out to study the characteristics of resistance for incompressible laminar flow in the rough tubes. The effect of relative height, relative length, angular width of roughness elements and Reynolds number on flow characteristics were numerically studied by employing the SIMPLE algorithm. The general trend can be observed that bigger sizes of roughness element lead to higher flow resistance. Particularly, the effect of roughness can no longer be ignored at relative roughness height higher than 3%, for the product of friction factor and Reynolds number can be up to 17% higher than the theoretical 64 in a macrotube.