流下液膜の遷移域

抄録

Wall shear stress for liquid film flowing down a vertical tube was measured by an electrochemical method using a slender band electrode attached circumferentially to the tube.
In the regions where Re _??_ 1000 and Re_??_ 150, the observed shear stress (τ_app) was in good agreement with the true shear stress (τ_w) estimated from mean film thickness. In the intermediate region, however, τ_app was markedly smaller than τ_w and the maximum difference was about 30%.
Based upon theoretical analysis, it was indicated that the ratio τ_w/τ_app was equal to 1.0 for turbulent and laminar flows and was greater than 1.0 for flow in the transitional zone.
By taking experimental and theoretical results into account, it was deduced that the transition to turbulent flow occurred in a definite range of Re, i. e. 150_??_Re_??_ 1000.