Wicking with a yield stress fluid

This work presents an experimental investigation of the flow of a model yield stress fluid ( yield stresses between 5 and 21 Pa) driven by capillarity in horizontal glass tubes with diameters ranging from 0.46 to 1.5 mm. It is shown that the liquid penetration stops after typically a few centimeters. The results disagree with a simple model based on the balance between capillary and frictional forces, suggesting that the yield stress fluid constitutive equation may not be valid in the immediate vicinity of the wall. Scaling is proposed with respect to a dimensionless number comparing the yield stress with the capillary pressure.