This is a keynote lecture before my retirement as the co-chairman of the European Japanese Two Phase Flow Group. On this special occasion I would like to review some of the key points that I started working on 40 years ago and have created very strong bonds with my Japanese friends. The joint results have proven to be crucial in the field. The development of the basic conceptual viewpoints that were opened at that time on the transient characteristics of turbulent bubbly flow in a vertical duct are reviewed with respect to the first archival papers on void fraction profiles in bubbly flow by Serizawa et al. in 1975, transverse lift force acting on the bubble by Žun in 1980, and momentum and heat transfer in bubble flow by Sato et al. in 1981. Later, Serizawa and Kataoka (1994) assumed that interactions between the bubble wake and the liquid shear field might be the reason for the observed lateral segregation of deformed bubbles in the opposite direction as expected from the classical lift force. Based on numerical investigations, Tomiyama et al. (1995) confirmed this presumption and related the inversion of the direction of the bubble migration to the presence of a slanted wake behind the deformed bubble. Bubble wake drift is the consequence of a significant interaction between the bubble interface and the surrounding liquid and is dependent upon the bubble size (Tomiyama et al. 2002a). There are unresolved questions regarding the initial conditions that were first pointed out by Tomiyama et al. (2002b). Additional problems arise when one wants to deal with complex multiscale phenomena. Complex bubbly flow is comprised of different scales, which makes it almost impossible to consider all simultaneous interactions at the same time (Zun 2002). In contrast to what the papers refer as the dynamic view point in two-fluid models, in most cases the inverse dynamic methods are being used, which automatically determine the force functions required to accomplish a stated goal. In extreme cases this may lead towards empirical fitting, which may drift us away from realistic multiscale physics. However, rapid progress in computer performance and corresponding numerical methods gives us a good prospect of realizing detailed numerical simulation of the two-phase flow. Among those, the interface tracking scheme implemented with non-uniform subcell scheme provided considerable improvement in our understanding of single bubble behaviour (Hayashi and Tomiyama 2007, Zun et al. 2012). Recently, progress has been made in the case of interfacial breakup in a manifold, which leads us towards the prediction of initial conditions based on prescribed mixing at continuous flow rates of both phases (Gregorc and Zun 2013). By only changing the prescribed flowrates, different two-phase flow patterns can be simulated. At the end of the presentation, very recent results of numerical predictions obtained at LFDT based on the high performance computing of gas jet breakup in a highly turbulent liquid cross flow will be shown for the first time. The results are validated by a corresponding experiment and show the simulation capabilities of coupled LES and VOF numerical schemes. Altogether, ten experimental set-ups developed at the Laboratory for Fluid Dynamics and Thermodynamics (LFDT) are presented and discussed in terms of physical and numerical modeling of bubbly flow. The following inlet configurations are included: (I) localized, forced inlets by jets or nozzles, (II) highly distributed “inlets”, including porous mixer, sparger, and vapor generation at cavitation nucleation sites, (III) volume mixing by suddenly imposed body forces.
B.01 Organiser of a scientific meeting
COBISS.SI-ID: 14351387The European Two-Phase Flow Group (ETPFG) was established in 1963, at the Royal Institute of Technology in Stockholm. Professor Becker, who at the time held the chair of Reactor Technology at the Royal Institute of Technology, was the founder. Further technological development revealed a whole new scientific methodology for understanding, as well as a whole new engineering apparatus in wide spectrum of practical applications in the industry and in medicine. The significance of new emerging scintific discipline was well pointed out in Scinece in 1999 quoting that ”Even simple cases reveal multiphase flows as a class of non-linear adaptive systems, an immense frontier of science in the 21st century ” In 1998, Prof. Žun founded on the highest principles of different scools of thoughts the first joint European-Japanese Two Phase Flow Group Meeting in Portorož by connecting ETPFG with the "Japanese Society for Multiphase Flow".Joint meetings since then successfully lined up on the Japanese and European territories every third year. The main objectives of the meeting are the latest reports on research achievements, sinergy of academic and economic circles and special concern for the younger generation. On October 13, 2015, a Plaque of Appreciation to the Founder of the European-Japanese Two-Phase Flow Group Meeting was presented to Professor Iztok Žun at the 7th European-Japanese Two-Phase Flow Group Meeting in Zermatt in the presence of more than 70 invited participants.
E.02 International awards
The subject of the invention is a process device for coating particles that falls within the field of chemical and pharmaceutical technology. It represents an improvement on the process equipment for coating particles by bottom spraying and works on the principle of solid particles fluidization. The improvement was achieved with the new swirl flow generator design. In addition, the improvement of the conventional Wurster coater was attained by installing slots for additional air inflow in the chamber. Compared to the conventional Wurster coater, both construction improvements enable better coating film uniformity and coating process robustness. The new design reduces the mutual shading of particles within the range of dispersion scattering and prevents the formation of stagnation zones. Up to 60% improvements of the coating uniformity can be achieved. The functionality of the coating is therefore achieved with less coating material, with lower power consumption and in shorter production times. A patent is an accomplished international enforcement (USA in 2014, Eurasia in 2015, also applied in the EU and in India). The development of a complex process of the device was only possible with the interdisciplinary integration of several partners: Faculty of Mechanical Engineering, UL, Faculty of Pharmacy UL and BRINOX Manufacturer of Process Systems. The ongoing collaboration started in 2009 and is aiming now towards the design of semi-industrial and industrial size devices. This would place Brinox on the list of world leading manufacturers of such systems
F.08 Development and manufacture of a prototype
COBISS.SI-ID: 12184091Particle concentration in a coating zone of fluid bed coater is important to ensure appropriate coating uniformity and process yield. A transmissive optical setup at the top of the Wurster draft tube was used in a lab scale coater. Measured transmittances were converted to volume fraction distributions using results of Monte Carlo calculations. The effect of gap between the draft tude and distribution plate, fluidizing air flow rate, particle size and load was studied. The ranges of measured transmittances were from 0,002 to 0,285 which corresponds to the range of volume fraction from 1,36% to 5,44%. Comparison of volume fraction results with quick closing hatch, CFD simulations, and coating experiments were also performed. In order to study the dynamics of the system as a function of different process parameters frequency analysis of transmittances signals was performed. Four distinct frequency responses were identified.
B.03 Paper at an international scientific conference
COBISS.SI-ID: 3897713