13th Int Symp on Applications of Laser Techniques to Fluid Mechanics Lisbon, Portugal, 26-29 June, 2006 Application of PIV to Velocity Measurements in the Liquid Film Flowing Down Inclined Cylynder Sergey V. Alekseenko 1 , Vladimir A. Antipin 1 , Alexey V. Bobylev 1 , Dmitriy M. Markovich 1 1: Institute of Thermophysics, Siberian Branch of RAS, Novosibirsk, Russia, dmark@itp.nsc.ru Abstract PIV technique is applied for measurements of instant velocity distributions in liquid film flowing down inclined tube in the form of rivulet. Additional optical calibrations allowed to correct distortion effects caused by curvature of interface. Vortex flow of liquid is observed inside wave hump in reference system moving with wave phase velocity. Conditionally averaged profiles for longitudinal and transverse components of liquid velocity are obtained for different cross-sections of developed nonlinear waves. It is shown that the rising of wave amplitude slightly change location of the vortex centre. The analysis of modification of vortex motion character due to wavy flow conditions, such as tube inclination angle, film Reynolds number, excitation frequency, is fulfilled. 1. Introduction Three-dimensional liquid films (rivulets) flowing down inclined tubes are the common features of hydrodynamic regimes in the numerous technological processes and installations (heat exchangers, absorbers, distillation columns, etc.). The waves appearing on the rivulet surface strongly affect heat- and mass transfer intensity through a number of mechanisms. Similarly to two- dimensional liquid films (Alekseenko et al., 1996, Park & Nosoko, 2003) the most intensification of heat- and mass transfer takes place at the flow regimes with developed non-linear solitary-type waves. To describe and control this intensification, primarily, the flow structure including velocity fields inside wavy film is necessary to be studied. The fundamental question is an existence of local vortices in the large solitary waves, which can be one of the issues for essential intensification of the transfer. Moreover, the mechanisms of drops entrainment from the film surface can also be correctly described only on the basis of velocity field analysis. At present, the measurement of velocity fields in wavy films is very complicated problem because of small film thickness and existence of high velocity gradients inside the film. At the same time, obtained empirical information about velocity field inside wavy film makes it possible to describe the mechanisms of momentum and energy transfer and can represent a basis for construction of adequate mathematical models. While spreading over flat plate the rivulets usually move in the form of nonuniform and nonstationary S-turn due to the existence of contact angle hysteresis (Towell & Rothfeld 1966). Dimensional analysis and experimental observations carried out by Kim et al. (2004) revealed the fact that contact angle hysteresis strongly affect curvature radius of rivulet. Analytical and numerical modeling of stationary rivulet flowing down inclined plate was performed by Carlos et al. (2004) and allowed to define the shape of a free surface and calculate velocity field. Myers et al. (2004) constructed an analytical model for a thin rivulet moving under effects of gravity and interfacial friction. In the work by Holland et al. (2001) the rivulet flow on heated or cooled (relatively to the environment temperature) surfaces was investigated. It was shown numerically - 1 -