Effect of the Coating Layer on the Apparent Viscosity in a Pipe Flow.

Abstract

The effect of a coating layer on the apparent viscosity of water in a tube is evaluated experimentally over a wide range of Reynolds-numbers (200-2000). In this study, a gelatin-coated glass tube, a paraffin-coated glass tube and a glass tube without a coating are used. The conclusions are summarized as follows: 1) At a low Reynolds-number region (20-500), the gelatin layer has the effect of decreasing the apparent viscosity by about 4%, but the paraffin layer does not have an effect on the apparent viscosity. 2) At a high Reynolds-number region (1000-2200), the gelatin layer suppresses the increase in the apparent viscosity due to the turbulent transition and a similar effect occurs in case of the paraffin layer.