Bao Fubing

Effect of Molecular Interactions between the Solid Wall and Liquid on the Flow Properties in Microtubes

The flow properties in microtubes, such as velocity profiles and pressure distributions, are different from those in macrotubes. We attribute this phenomenon to the molecular interactions between the solid wall and inner liquid. The apparent viscosity, which takes into consideration the molecular interactions, is introduced in the present study and the Navier–Stokes equations are solved. Water is adopted in the calculation. For the hydrophilic material wall, the water is more like to adhere to the wall. The velocity near the wall is smaller than that of conventional theory, while the centerline velocity and pressure gradients are much larger. Such a phenomenon becomes much more obvious with the decrease in tube diameter.

Equivalent thickenss of materials of fused silica and stainless steel in the flow of microtubes

The deviation of flow characteristics from the predictions of the conventional theory for microtubes was attributed to the change of fluid viscosity resulted from the interactions between the molecules on solid wall and in fluid. The degree of this departure is dependent on the microtubes materials. A concept of equivalent thickness with which conventional theory can be used to predict the flow in microtubes without modifying the fluid viscosity was put forward. The values of equivalent thickness for fused silica and stainless steel materials were determined as 1.8 μm and 1.5 μm, respectively, by repeated numerical simulation.