Table Of ContentDiss. ETH No 16220
Experimental Investigation of Large-Scale Three Dimensional
Bubble Plume Dynamics
A dissertation submitted to the
Swiss Federal Institute of Technology Zurich
for the degree of
Doctor of Technical Sciences
presented by
Marco Simiano
born March 20, 1976
Master of Science - Nuclear Engineering
Palermo University, Italy
citizen of Italy
Accepted on the recommendation of
Prof. Dr. G. Yadigaroglu, examiner
Prof. Dr. T. R¨osgen, co-examiner
Prof. Dr. M. Lance, co-examiner
Dr. D. Lakehal, co-examiner
2005
Certainties....
Something unknown is doing we don’t know what
Sir Arthur Eddington (1882 - 1944)
I would never die for my beliefs because I might be wrong
Bertrand Russell (1872 - 1970)
Acknowledgement
This work was funded by the Paul Scherrer Institute (PSI) in Villigen, Switzerland, and
by the Emil Berthele Fonds, Switzerland. Part of this work has been carried out within
the ASTAR project of the 5th Euratom framework programme Nuclear Fission, with
financial support from the Swiss Federal Office for Education and Science under contract
No. 99.0796. These supports are also gratefully acknowledged.
Above all, I would like to thank Prof. George Yadigaroglu of ETH Zurich who gave
me the great opportunity to work on this project. He was always ready to bring fruitful
suggestions and provide invaluable help and motivation. I am also thankful to Prof.
Thomas R¨osgen of ETH Zurich for his agreement to be my co-referent and his helpful
comments and suggestions on the draft of the present work; to Prof. Michel Lance from
Ecole Centrale de Lyon, for agreeing to be co-reviewer of this thesis. He, together with
Prof. G. Yadigaroglu, inspired the idea for the technique I used in the second part (Part
II) of this work to record the three dimensional movement of the bubble plume.
I must particularly thank Dr. Francois de Cachard of PSI, who was not only a su-
pervisor, but also he helped in many circumstances, especially at the beginning of this
experience; Dr. Djamel Lakehal of ETH Zurich for his continuous contribution to this
project and for bringing invaluable help with his deep experience in turbulent flows; Mr.
Max Fehlmann for providing me technical solutions for all the modifications of the facility
during the experimental campaign.
SpecialthanksgotoDr. Robert Zboray ofPSIwithwhomIcloselycollaboratedduring
the ASTAR project. He also provided me with some of the measurements reported in
Part I and introduced me to the Matlab world.
Many thanks go to Dr. Michele Andreani of PSI for his suggestions and his huge
knowledge of the literature in two phase flows, to the senior staff of LTH, from Dr.
Joerg Dreier, Head of the Laboratory, to our Secretary Mrs. Verena Knecht for their
help. I would like to thank Dr. Domenico Paladino and Dr. Olivier Auban for their
friendshipduringthoseyears, Daniele Cannavo forhisgeneroushelpwithLabviewandhis
i
friendship, Dr. Narayanan Chidambaram for his invaluable help in many circumstances
and finally Prof. Michele Ciofalo who, being the assistant supervisor of my master thesis,
initiated me into the world of the research.
During the last four years in Switzerland I met many people which, I am sure, will
be my folk for the rest of my life. Without them, my life in Switzerland could have been
very difficult. Therefore, I would like to start by thanking Andrea Ciani alias Chano (who
introduced me to the Polemics’s World) and Marco Santis alias The Prophet (who sees
what others do not) for the many nice moments we had together.
I would also like to thank some other great people I met in Switzerland who were,
rather than friends or colleagues, a family: Elena who was always there for me, Lale
for being Lale (sorry for the tautology), Christine who introduced me to the BIO world,
Gloria for being a very good friend and letting me practise my Spanish, Marco Fulgosi for
being my Latex mentor and, for a short-time, also a great roommate, Lavinia for showing
me some of the nice aspects of Zurich, Salvo with whom I shared a house and friends for
the first year, Enrico for being a good friend and always letting me win at squash, Luca
and Rania the greatest greak-roman cocktail and Erik for teaching me the art of swearing
in English.
A special thank you goes to Boni Boniello who, with a lot of love and patience, helped
me on the review of this script.
I must also thank all of the people from my home; Sicily, for their love, invaluable
support and motivation.
My long-time friends: Fabrizio alias Frank with whom I shared a long part of my
education time, Tommaso alias Pallonaro my closest buddy, Alessandro alias Benzo for
being my friend before my cousin, Toti alias Pigghiala cocchi palla for not being my
dentist but being my good friend, Gianmarco for being a real brother, Alessia for what
we shared in the past, Pierluigi and Manfredi for all the nice times we experienced during
our studies in Palermo.
And last but not least, I would like to thank my parents Enzo and Marisa, my sister
Simona, my grandparents Nonno Ciccio and Nonna Iolanda and all my relatives who,
during the last four years, have always been very close despite the physical distance.
Abstract
The report is divided in two parts, reflecting the chronology of the research work perfor-
med.
The first part presents an extensive study of the most important hydrodynamic cha-
racteristics of fairly large-scale bubble plumes, created in a cylindrical vessel having a
diameter of 2 m with water depth of 1.5-2 m. The bubbles were produced near the bot-
tom of the vessel by a multi-needle circular injector having a diameter of 0.3 m. Several
measurement techniques and a variety of tools were used to measure and to analyze the
data. Particle Image Velocimetry (PIV), double-tip Optical Probes (OP), photographic
techniques and three-dimensional Electro-Magnetic Probes (EMP) were extensively app-
lied to measure bubble and liquid velocities, void-fraction, interfacial area concentration,
bubble size and liquid re-circulation rates. PIV measurements in a vertical plane crossing
the centre of the injector provided the instantaneous velocity fields for both phases, in-
cluding selected hydrodynamic parameters, such as the movement of the plume axis and
its instantaneous cross-sectional width. Statistical studies were performed using image
processing to determine the diameter and the instantaneous centreline position distribu-
tions and their fluctuations in time. An important finding was that there is not much
instantaneous spreading of the plume. The stress tensor distributions obtained from the
instantaneous data indicate that for the continuous phase, these stresses scale linearly
with the local void-fraction in the range of 0.5%< α <2.5%. The bubbles were found
to be approximately ellipsoidal, with shape factor e ≈0.5 an equivalent bubble diameter
(Sauter) of about 2-2.5 mm.
In the second part, the limitations imposed by measuring successively the flow para-
meters in each phase were eliminated. Indeed, since the velocities of the continuous and
discrete phases are strongly correlated, simultaneous velocity measurements are required
to estimate correctly the relative velocity. The PIV system was expanded with a second
camera, used to measure simultaneously the velocity fields of the two phases in the verti-
cal plane crossing the injector. In addition, a two-camera video recording system, stored
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simultaneous images of the 3D bubble plume structure so that the PIV data could be
categorized according to the state of the plume (position and width).
The instantaneous bubble and liquid velocity vector plots were correlated with the
corresponding instantaneous bubble plume images. This allowed sampling and ensemble
averaging of according to the bubble plume position or bubble plume diameter.
The three dimensional plume dynamics was intensively investigated. The large-scale
instability of the bubble plume resulted from meandering of the plume structure around
its axis with superimposed horizontal cross-section fluctuation, as already suggested from
the results obtained in the first part of the work.
The plume meandering and the horizontal cross-section fluctuation, supplied the in-
stantaneous measured quantities with a coherent contribution which appeared as a fluc-
tuation over the mean value.
The coherent contribution to the globally time-averaged quantities such as velocities,
Reynolds stress terms and therefore to the turbulence intensity was evaluated; the results
showed a negligible contribution close to the injector and a substantial one at higher
elevations. Thecoherentcontributionwassignificantinbothphasevelocities,butstronger
in the Reynolds stress terms and therefore in the turbulence properties.
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Sintesi
La presente dissertazione `e stata divisa in due parti rispecchiando la cronologia del lavoro
effettuato.
La prima parte presenta uno studio estensivo dei parametri idrodinamici piu` import-
anti delle grandi piume di bolle. Queste sono state create in un contenitore cilindrico con
un diametro di 2 m e con un battente d’acqua di 1.5-2 m. In questo studio sono state uti-
lizzate diverse tecniche sperimentali: velocimetria ad immagini di particelle (PIV), sensori
ottici a doppia punta (OP), macro fotografia digitale e sensori elettromagnetici (EMP).
Queste tecniche sperimentali hanno permesso di misurare rispettivamente il campo di ve-
locit`a della fase gassosa e del liquido, la frazione di vuoto, la concentrazione dell’area di
interfaccia tra il liquido ed il gas, la dimensione delle bolle ed il moto di ricircolo generato
dalla piuma di bolle.
Le PIV sono state eseguite in un piano verticale situato al centro del dispositivo di
iniezione delle bolle. Queste misure hanno fornito: i campi di velocit`a di entrambe le
fasi, il movimento dell’asse della piuma di bolle e la sua istantanea sezione verticale. Uno
studio statistico di questi ultimi ha permesso di determinare, processando le immagini ot-
tenute dalla PIV, il diametro e la posizione dell’asse della piuma. Importanti conclusioni
sono state dedotte da questo studio: l’espansione del core della piuma di bolle `e notevol-
mente inferiore all’espansione del profilo, mediato nel tempo, della velocit`a del liquido.
Le componenti del tensore di Reynolds, ottenute dalle misure PIV, sono proporzionali
alla media temporale della frazione di vuoto, α, nel range 0.5%< α <2.5%. Le bolle sono
ellittiche con un fattore di forma di circa 0.5 ed un diametro equivalente (Sauter) di circa
2-2.5 mm.
Nella seconda parte di questa dissertazione sono state eliminate le limitazioni dovute
allo studio di un flusso bifasico, misurando una fase alla volta. La stretta correlazione tra
le velocit`a della fase liquida e di quella gassosa ha reso necessaria una misura simultanea
delle due velocit`a per stimare correttamente la velocit`a relativa. Di conseguenza, un
nuovo sistema PIV si `e reso necessario per permettere misure simultanee. Inoltre, insieme
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