Minimum thickness of a flowing down liquid film on a vertical surface

Contact angles of water at its boiling point, measured on surfaces of copper and polytetrafluoroethylene, are reported for pressures ranging from 10–770 torr. The results suggest that not only impurities and oxidation have been responsible for the wide range of angles reported in the literature but that inconsistencies may be created because of an adsorbed layer of water vapour on the solid surface.

Wettability of copper and polytetrafluoroethylene surfaces with water—the influence of environmental conditions

Falling film on a vertical flat plate – Influence of liquid distribution and fluid properties on wetting behavior

Two models for breakdown of a heated draining film subjected to surface shear stresses are developed. The predictions compared favorably with experimental results obtained in a two-component downwards cocurrent flow in an electrically-heated tube, providing a dynamic contact angle of 110-120° is assumed. This is in agreement with results in Part 1 on a small perturbation theory. Possible explanations are presented, based among others on capillary dryout or adsorption temperature thresholds. Comparisons with literature data on film breakdown are also made.

A. B. Ponter

Papers

The rupture of isothermal vertical liquid films