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.