Influence of mass transfer on drop size distribution In an agitated liquid-liquid dispersion
Agata Maria Bąk , Wioletta Podgórska , Joanna Zenke , Edyta Leśniewska
AbstractChanges of drop size distribution in an agitated liquid-liquid dispersion are caused by breakage and coalescence processes which are dependent on drop size, rotational impeller speed, physical properties of continuous and dispersed phases (viscosity and density), volume fraction of dispersed phase and surface active agents, which adsorption on drop surfaces causes interfacial tension reduction. Film drainage rate and, finally, drop coalescence rate are also dependent on mass transfer between aqueous and oil phases. For processes such as extraction, suspension polymerization and emulsification it is important to increase total interfacial area, therefore, direction of mass transfer is important. If mass transfer is from continuous phase to drops, concentration of transported substance in liquid film created between two colliding drops is lower than outside the film. For decreasing interfacial tension function with increasing concentration of transported substance, interfacial tension in liquid film is, therefore, higher than outside this region. As a result, generated tangential stresses oppose film drainage and hamper drop coalescence. For opposite direction of mass transfer, i.e. from dispersed to continuous phase, generated tangential stresses due to interfacial tension gradient speed up film drainage and as a consequence, coalescence rate increases, decreasing total interfacial area. Experiments were performed for toluene-water-acetone dispersion in a completely filled, cylindrical (D = H = 0.15 m) and thermostated (25 0.1C) tank equipped with a six-blade Rushton turbine (Dimp = 0.05 m) and four equally spaced stainless steel baffles. Dispersion was lighted up by a halogen lamp through a glass-fibre light-conductor ended with a special tip placed inside the tank. Sequences of dispersion pictures were recorded by a high-resolution digital camera, connected with the computer and stereomicroscope objective. Toluene was used as a dispersed phase which occupied 5% of the total dispersion volume. In performed experiments the influence of acetone concentration and impeller rotational speed on transient drop size distribution and changes of Sauter diameter in an agitated liquid-liquid dispersion were considered. These results were also compared with results obtained for pure toluene-water dispersion. Additionally, interfacial tension was measured for applied two-phase systems. DVA1 (SINTERFACE) tensiometer was used in measurements.
|Publication size in sheets||0.3|
|Book||Cywińska Urszula (eds.): The 22nd Polish Conference of Chemical and Process Engineering, Spała, 5-9.09.2016. Book of Abstracts, 2016, EXALL, ISBN 978-83-61997-73-3|
|Keywords in Polish||transport masy, dyspersja ciecz-ciecz, napięcie międzyfazowe, przepływ burzliwy|
|Keywords in English||mass transfer, liquid-liquid dispersion, interfacial tension, turbulent flow|
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