Patterns of LiBr + water falling film in presence of surfactants

Several experimental studies reported the effective influence of the 2-ethyl-1-hexanol surfactant for the heat and mass transfer enhancement in absorbers operating with LiBr aqueous solutions. The fluid dynamics of the falling film is rather complex and the knowledge of the flow patterns is crucial for the understanding of the heat and mass transfer mechanism. An apparatus for experimental investigations of heat and mass transfer of LiBr + water falling film was built. A special test section was designed for visual observations of the falling film and for recording the related images by means of a video camera. A series of tests was run with 51.2 % LiBr aqueous solution without any corrosion inhibitor, being negligible the steam velocity; 2-ethyl-1-hexanol was added in concentration within the typical range used in LiBr absorption machines. The transition from one flow mode to another is investigated in relation to viscosity, surface tension and gravitational effects. For what is concerned with droplet and column patterns, the distance between droplets and rivulets is analysed with reference to the Taylor instability theory for thick films. Photos of the different flow modes over the tube column are presented in the paper.