Thickness and velocity of wavy liquid films on rotating conical surfaces

The thickness and velocity of the thin liquid films flowing up a rotating c one surface are among the key parameters determining mass transfer characte ristics and overall performance of gas-liquid contacting devices such as sp inning cone distillation columns and centrifugal film evaporators. Laminar model predictions for these devices are inapplicable under the turbulent fl ow conditions of commercial-scale equipment. In this work, dimensionless em pirical models for the average thickness and radial velocity of wavy films have been developed based on thickness measurements on a laboratory-scale c one. The experimental method registered the intensity of induced fluorescen ce of a flowing film illuminated by an ultraviolet light source. The film i s modelled as a wavy layer on top of a laminar sub-layer attached to the di sk surface. The thickness of the film is an additive modification of the Nu sselt model thickness delta (+) = delta (+)(N) + delta (+)(wave) = 0.91 eta (-2/3) + 1.95 eta (-3) where eta is a normalised radial distance. The thic kness of the wavy layer delta (+)(wave) has been correlated with 95% confid ence limits of +/- 12%. In the dimensional form, the proposed models expres s the film thickness and radial velocity as functions of cone geometrical a nd operating parameters. The validity of the models is consistent with inde pendent velocity measurements on a rotating cone and film thickness measure ments on rotating disks. The normalised film thickness is shown to be essen tially preserved for spinning cone columns of varying size scaled at consta nt relative capacity. (C) 2001 Elsevier Science Ltd. All rights reserved.