Average velocity distributions within falling liquid films

Abstract

A photochromic dye-tracer technique was developed and used to measure the velocity distributions within falling liquid films inside a vertical pyrex tube. Three liquids with similar densities and surface tensions but different kinematic viscosities were used and the Reynolds numbers (4 Q/ v) investigated ranged from 124 to 2800. The fully-developed average velocity distributions were found to be a function of the Reynolds number alone and independent of the distance from the liquid inlet. In dimesionless parameters, the average velocity distributions can be represented by the equation ▪ The average film thicknesses calculated from the wall shear stresses agreed well with values obtained with other direct measurement methods.