752 Chemie Ingenieur Technik (73) Multiphase Systems equations for the flow field combined with a front tracking method to resolve and move the deformable bubble interfaces within the surrounding liquid. The goal of these investigations is to evaluate the dependency of bubble interactions, bubble rise velocities, and bubble-induced liquid turbulence on bubble size and deformability, bubble size distribution, and gas volume fraction in order to support the modelling of turbulent dispersed multiphase flows. The evolution and statistical behaviour of various bidisperse bubble systems are compared to those of monodisperse systems. 520* Unsteady Conjugate Mass Transfer in Single Drop Systems P r o f. D r. - I n g . M . K r a u m e D r. A . Pa s c h e d a g IR. W. H. Piarah Dipl.-Ing. K. Schulze Technical University Berlin, Department of Chemical Engineering, Straûe des 17. Juni 135, D-10623 Berlin/Germany, Tel.: +49 30 314-23701 Fax: +49 30 314-21134, E-mail: vtsekr@ivtfg1.TU-Berlin.de Mass transfer between a single spherical drop and a surrounding fluid flow has been analysed. The physical properties of the system lead to a conjugated mass transfer problem. The mass balance equations are solved numerically. The influence of the Pe number (up to 105) on mass transfer is studied at higher Re numbers (Re = 100). The results are shown in the form of local and averaged Sherwood numbers. Internal and external mass transfer resistances are determined. It is shown that with increasing Pe numbers the internal resistance becomes important which is of special interest as in the case of typical technical applications more than 80 % of the mass transfer resistance are due to the internal transport process. 521* Induced Pulsing Flow in Trickle Beds ± Characteristics and Attenuation of Pulses D. Giakoumakis M. Kostoglou A. J. Karabelas1 Department of Chemical Engineering, Aristotle University of Thessaloniki & Chemical Process Engineering Research Institute, P.O. Box 1517, University Campus, GR 540 06 Thessaloniki, GREECE. 1 Tel. 30-31-996201, Fax 30-31-996209, E-mail address: karabaj@cperi.certh.gr Induced pulsing flow is studied as a method of process intensification and overall improvement of trickle bed performance. This mode of operation involves periodic liquid feeding, to an otherwise steadily operated trickle bed reactor. New data are summarized here, obtained with three symmetric cyclic frequencies of liquid 6 I 2001 feeding. Key parameters for characterization of evolving liquid pulses (such as pulse intensity p and celerity C) are obtained by measuring the temporal variation of dynamic liquid hold-up hd at various levels of the packed bed. These parameters show that the pulses tend to decay, as they more down the bed, in a way reminiscent of convection- diffusion processes. A simple phenomenological model is developed along these lines, involving a single parameter for representing pulse attenuation. Values of this attenuation parameter (for various gas and liquid flow rates) show interesting trends amenable to correlation. 522* Aerodynamic Characteristics of FGD Spray Towers ± The Influence of Spraying Angle and Droplets Polydispersity Jacek A. Michalski Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland, Jacek@ichf.edu.pl A model predicting aerodynamic characteristics of FGD scrubber with polydispersed spray is developed on the basis of two-dimensional, non stationary droplets motion. The model predicts pressure drop caused by spray, concentration of dispersed phase and its residence time in the system. The effects appearing due to spray polydispersity and two-dimensional droplets motion are discussed and explained. 523* Experimental Observation of the Behaviour of Single, Small Bubbles in a Quiescent Fluid and Their Wakes H. Sauter V. H e i n z e l Forschungszentrum Karlsruhe, Institut fuÈr Reaktorsicherheit, Postfach 3640, D-76021 Karlsruhe/Germany In this report we characterize different types of flow around a single rising bubble for the validation of simulation model calculations by elaborating typical factors exercising the most intensive impacts on the wake. We used deionated water, sometimes mixed with a few percent ethanol as a stagnant fluid in a test cell, and synthetic air as a gas. We produced small bubbles only, with limited deviations from a rectilinear rising path. For start up, we investigated the life time of the wake behind the bubble so that the requirement of rising ªsingleº bubbles in quiescent water could be fulfilled. We used non-invasive optical methods like photographing and lightbarrier measurements for speed and path observations as well as invasive methods to test the aptitude of hot wire anemometry, LDA and PIV. Also the slightly invasive, but very versatile and sensitive Schlierenmethod was applied to visualize details in inner and outer wake behaviour.