AN EXPERIMENTAL-STUDY OF FREELY FALLING FILMS IN A VERTICAL TUBE

A laser-induced photochromic dye tracer technique has been applied to investigate the hydrodynamic structure of free falling liquid films in side a vertical tube (ID = 50.8 mm) over the film Reynolds number (Re- L = 4 Gamma/mu) range of 1408-6549. :Flow visualization data indicated significant differences between the measured velocity profiles and Nu sselt's predictions in wavy turbulent films. Also, the experimental da ta have shown that wave-induced turbulence produces a flat velocity pr ofile within the large disturbance waves and also affects the flow in the substrate film depending on the wave amplitude. Present data clear ly indicate that the large disturbance waves do not carry large fracti ons of the liquid mass as previously believed. (C) 1998 Elsevier Scien ce Ltd. All rights reserved.