Observation of a dynamic wetting process using Laser-Doppler velocimetry
Article first published online: 17 JUN 2004
Copyright © 1989 American Institute of Chemical Engineers
Volume 35, Issue 9, pages 1521–1526, September 1989
How to Cite
Mues, W., Hens, J. and Boiy, L. (1989), Observation of a dynamic wetting process using Laser-Doppler velocimetry. AIChE J., 35: 1521–1526. doi: 10.1002/aic.690350912
- Issue published online: 17 JUN 2004
- Article first published online: 17 JUN 2004
- Manuscript Revised: 14 JUN 1989
- Manuscript Received: 3 JAN 1989
The purpose of this study is to observe the dynamic wetting process of a slide coater flow (Ca = 0.16; Re = 14.4; St = 0.0142; ΔeP = 2.5), using a specially-developed Laser-Doppler measuring technique.
The measurements, carried out with glycerol solutions, reveal that the observed contact line is apparent and that a thin air film is entrained between the web and the liquid surface. The liquid is accelerated along the lower free surface and attains approximately 50% of the web velocity at the apparent contact line. Downstream from the apparent contact line, the liquid is further accelerated along the air film to the web velocity at the real contact line.
The apparent contact angle increases with the capillary number Ca and air entrainment occurs at Ca = 0.25.