Bubble Deformation in Nucleate Boiling

July 14, 2014 08:40

Abstract: Nucleate boiling is one of the most efficient modes of heat transfer, yet many aspects of nucleate boiling are not well understood even today. Important aspects of nucleate flow boiling currently under research are the interactions of • an isotropic growing bubble with approaching flow • shape deformation and bubble detachment with flow and angle of inclination • neighboring bubble nucleation sites The onset of nucleate boiling and the net heat transfer coefficient are heavily influenced by these interactions. At the same time, the predictive capacity of mechanistic heat transfer and pressure drop models suffers from a lack of knowledge of these interactions. This paper intends to survey the present state of knowledge of these interactions, including some interesting recent findings.

There are two main force balances acting on the center of mass of a growing boiling bubble. One is parallel to the presumably plane wall which heats the flow. The other is normal to this wall. This normal component is often used for a criterion to predict bubble size at detachment. Bubble is then said to have departed from the wall if its gas-liquid interface is closed. The force components parallel to the wall may cause the bubble to "slide" over the wall before actually departing. Whether the contact line is actually moving in this case is questionable. However, next to these two force components other forces govern growth and detachment of a bubble in forced convection. They are related to bubble deformation and the most well-known and significant dynamic relationship involved is often named after Rayleigh and Plesset. The more complex the shape deformation, the more force balances must be taken into account. A coupled set of second order differential equations governs bubble growth dynamics in the general case. In each of these governing equations drag occurs. Drag is partly related to vorticity. Two areas or layers with significant vorticity built up can be distinguished in the liquid in nucleate boiling. The layer adjacent to the wall which exists in single phase flow and which is heated by the wall is one. The downstream wake of a bubble is the other. Quite often bubble growth rate is that fast and viscosity is that small that vorticity built-up in the wake is negligible and hardly contributing to the drag on the bubble. The main force components are then given by capillary action and by the overpressure inside the bubble. These two forces are enormous and nearly balancing one another. The difference is finely tuned by shape deformation and compensates gravity and -if the bubble volume is significant or bubble deformation is large- inertia forces. The process conditions in which the above relative force estimations are valid will be specified in the paper. Various independent ways to assess the force components from measured bubble growth histories will be discussed. Several validation examples will be shown, some for pool boiling, others for forced convection in micro- and in terrestrial gravity.

The bubble size at detachment depends, amongst others, on orientation of the heated plate with respect to gravity, on the velocity profile of the flow approaching the bubble and on the system pressure. Physical properties in the Jakob number cause this number to increase with decreasing system pressure, which decreases the overpressure inside the bubble and, hence, decreases the corresponding detaching force component as well. At the same time, a slight increase in the adhering capillary force is caused by the decrease in system pressure and the corresponding decrease in saturation temperature. Both effects increase the bubble size at detachment with decreasing system pressure, a trend often observed. The bigger the bubble, the more important inertia forces are and the more sensitive the growing boiling bubble is for acoustic triggering or for disturbances of a different nature. Force analysis of pool boiling bubbles at low system pressure reveal the importance of inertia forces of strongly deforming bubbles. The number of eigenmodes of a bubble attached to a plane wall exceeds that of a free bubble by one, because rectilinear motion of the center of mass loses symmetry by introduction of the wall. With a dedicated experiment, the relation between the frequency of this additional eigenmode and geometrical properties of an attached bubble has been measured. Theoretical analysis predicts the radian frequency found, as well as other frequencies such as the high one connected to isotropic deformation, f_RP, and shape deformation frequencies, f_n. Boiling bubbles have been triggered acoustically in the audible regime at various frequencies around bubble eigenmodes. Precisely at predicted frequencies of f_RP and f_n a decrease in bubble size at detachment and an increase in bubble release frequency have been found. Theoretical analysis shows that in principle another type of resonance might occur if 4f_n^2 is forced to become close to f_RP^2. However, sustained large amplitude oscillation in the near-resonance case always involves more than one fundamental mode. The nearby presence of a wall merely enhances this effect of cross-over of fundamental modes. The frequency f_n is found to decrease with increasing amplitude and with decreasing distance to a plane wall. Nucleation site interactions were extensively studied in pool boiling, which provided better insight in the phenomenon. Only recently these interactions have been studied in a flow boiling setup (Coen Baltis). Several bubble generators have been equally spaced and operated independently. High speed camera recordings at 5,000 fps have been synchronized with instantaneous voltage and power measurements of the bubble generators at 10 kHz data acquisition frequency. The added convective heat of an upstream generator is found to promote bubble nucleation at a downstream site up to the point when the upstream generator starts to create boiling bubbles of its own. From this moment on, the bubbles originating from the upstream generator have an inhibitive effect on bubble frequency of the downstream generator and can even cause deactivation of bubble nucleation. Another very interesting discovery was made during these experiments, which will be discussed in the paper.

Bio: Cees van der Geld (1954) was appointed associate professor Multiphase Flow in 1990, after working one year in industry, obtaining a Ph.D. in 1985 and working for 2 year at Aerospace Engineering at TU Delft. His main field of research is phase transitional flows, in particular flows with boiling, condensation and steam injection. Focal points have been quantification of added mass forces on deforming bubbles, theoretical and experimental determination of drag and lift forces during bubble detachment and bubble/particle motion in turbulent flows. Also drop drainage and dropwise condensation in compact heat exchangers were studied.

• President of the Assembly of World Conferences on Experimental Heat Transfer, Fluid Mechanics and Thermodynamics (AWC). Chairman of the Nusselt-Reynolds prize committee in 2009-2013
• Editor of Experimental Thermal and Fluid Science. Frequent reviewer for high-ranked journals
• Member or co-chair of organizational committees of various conferences, e.g. in Poland, Jamaica, China, Italy. Chairman of the contact group Two-Phase Flow in the Netherlands in 1987-2003
• Member of various international scientific committees, such as the standard committee ISO/TC 185/WG 1 Working group Two-phase flow.
• Representative of Eindhoven University for the CAPES-funded BRANETEC program for exchange of students with Brazil.
• Coordinator of over 100 MSc thesis, co-advisor of 15 PhD students, member of 6 Ph.D. committees abroad

Cees was in the period 2001-2009 (co-) author of 27 refereed journal papers, in the period 2010-2012 of 17 refereed journal papers. Recent cooperation with the Amsterdam Medical Centre and Erasmus Medical Centre (Rotterdam) resulted in 14 articles, so far. In 2007-2013 was Cees involved in 12 subsidized projects, 9 times as principal investigator and mostly funded by the Dutch Technology Foundation STW. XXX

Multiphase Flow and Heat Transfer on Micro/Nanostructured Surfaces

July 14, 2014 09:20

Abstract: Multiphase flow and heat transfer in mini/microspaces are of significant interest for thermal management applications, where the latent heat of phase change offers an efficient method to dissipate large heat fluxes in a compact device, such as a heat spreader or a heat pipe. However, a significant challenge for the implementation of microscale phase change heat spreader is associated with flow instabilities due to insufficient bubble removal, leading to liquid dry-out which severely limits the heat removal efficiency. Specifically, in the micrometric scale, the relative importance of surface tension and viscous forces become predominant compared to inertia and buoyancy forces. Because the instability of micro/nanobubble formation and breakup is sensitive to the interfacial surface tension, and the temperature distribution, due to the wettability of the surface, the capillary forces are particularly sensitive to the geometry of the surface wettability patterns. Vapor bubbles generated on the micro/nanostructure wettability patterned surfaces may create instability of bubble dynamics that may have the potential to enhance heat transfer and critical heat flux from the surfaces. To address this challenge, several techniques have been proposed to enhance two-phase flow and heat transfer in mini/microspaces.

This work will conduct a review on the challenges and opportunities that surfaces with micro/nanostructure patterned wettabilities. Bubble dynamics, fluid flow and heat transfer caused by the micro/nanostructure patterned surfaces will be discussed. The effects of micro/nanostructure patterned surfaces on flow generation under a vapor bubble in a microchannel under very low Reynolds number will be demonstrated. The effects of wettability patterned surfaces on nucleation pool boiling and flow boiling heat transfer processes will be described. Bubble formation, breakup and departure will be visualized and measured. It is found that bubble dynamics and pool boiling performance are enhanced significantly on smooth and flat surfaces combining hydrophilic and hydrophobic patterns in comparison with a hydrophilic surface. Wettability patterned micro/nanostructure surfaces are manufactured on glass wafers and copper surfaces, respectively. Different surface hexagonal pattern size will be used. Indium Tin Oxide (ITO), Fluoroalkylsilanes (FAS) and Copper Oxide (CuO) will be used for glass and copper surfaces, respectively. It was found that a micro/nanostructure patterned surface can significantly improve the nucleation process which has great potential for enhancing heat transfer. Fluid flow and boiling heat transfer in microspaces with patterned surfaces will be discussed. An asymmetrical heat spreader with Micro/nanostructured evaporator will be demonstrated. Bubble dynamics and heat transfer in a mini/microspace under acoustic excitation will also be presented, which can further enhance heat transfer in mini/microspaces.

Bio: Dr. -Ing. Huihe Qiu is presently a Professor and Associate Head of Mechanical and Aerospace Engineering Department at The Hong Kong University of Science & Technology (HKUST) and Associate Director of the HKUST FYTGS Building Energy Research Center. His academic career started with a Bachelor's and a Master's degree in 1982 and in 1985, respectively, both from Tianjin University, China, followed by a Ph.D. degree from Institute of Fluid Mechanics, LSTM, at the University of Erlangen, Germany in 1994. Professor Qiu's research areas are in multiphase flows and heat transfer, optical diagnostics and transport phenomena in nano- and microfluids. Professor Qiu is Editor-in-Chief of Case Studies in Thermal Engineering (Elsevier), associate editor of Aerospace Science and Technology (Elsevier) and more than 10 editorial board members of international journals, such as Experiments in Fluids, etc. He was the Guest Editor of the special issue of Experiments in Fluids (Springer) and Guest Editor for Special Issue of Communication in Computational Physics (CiCP). Professor Qiu is the General Chair of 4th Asian Symposium on Computational Heat Transfer and Fluid Flow (2013), Co-Chairman of 8th Asian Computational Fluid Dynamics Conference (2010) and Vice Chairman of 9th Asian Symposium of Visualization (2007) and keynote speakers in 4th International Conference on Jets, Wakes and Separated Flows in Nagoya, Japan (2013) and keynote speaker in 8th International Symposium on Measurement Techniques for Multiphase Flows, Guangzhou (2013). He is the recipient of the Best Paper Award of Measurement Science & Technology, Institute of Physics (IOP) in 1994; the Highlight of the year from Measurement Science & Technology (IOP) in 2005, the Highlights of the year from Journal Micromechanics and Microengineering (IOP, 2009 and 2011); Mosaic 2007 Measurement Science & Technology (IOP); ASME Best Poster Award, ASME International Mechanical Engineering Congress & Exposition (2010), Philips Outstanding Paper Award in ICEPT-HDP (2012); The State Scientific and Technological Progress Award (SSTPA) and the Scientific and Technological Achievement Award from the State Education Commission.

On Conservation of Scattered Energy and Angle in Radiative Transfer Computations

July 14, 2014 09:20

Abstract: To compute accurately radiative transfer in anisotropically-scattering media, conservation of both scattered energy and angle after discretization is required. Alteration of asymmetry factor (i.e., average cosine of scattering angles) due to angular discretization leads to a third type of numerical error, named as angular false scattering. The error that was known as "false scattering" is actually caused by spatial discretization and has nothing to do with scattering; and thus, it is more appropriate to be called "numerical smearing". Five phase-function normalization techniques, designed to attempt to conserve scattered energy, angle, or both, are analyzed here using DOM and FVM for both diffuse and ballistic radiation, to determine their capability to mitigate errors and produce accurate radiative transfer. Comparisons with Monte Carlo benchmark predictions are used to gauge accuracy. The two normalization techniques that conserve both scattered energy and asymmetry factor simultaneously are found to result in substantial improvements in radiative transfer accuracy with respect to MC predictions and comparison to each other. Normalization for ballistic radiation situations is shown to be crucial. Normalization impacts FVM and DOM in similar manners, as the accuracy of both is equal. In terms of computational efficiency, it is found that the DOM is more efficient than the FVM when both have the same number of angular directions.

Bio: Dr. Zhixiong Guo is a tenured full Professor of Mechanical and Aerospace Engineering at Rutgers University-New Brunswick, USA. He is a Fellow of American Society of Mechanical Engineers (ASME). His research spans a wide area of heat and mass transfer, with notable expertise in thermal radiation, laser applications and diagnostics. He is a pioneer in ultrafast laser radiation transport modeling and experimentation. His novel work on single molecule detection has been highlighted by IOP. He has also received a teaching award from Rutgers Vice President Office for Undergraduate Education. He has supervised 10 PhD students and 7 visiting/postdoctoral scholars. He is the author or co-author of over 80 research articles in archival journals. Currently he serves as an associate editor for ASME Journal of Heat Transfer and international journal Heat Transfer Research. He also serves in the editorial board of several other journals, and in the organization or scientific committee of several international conferences. He was a Co-Chair of two International Workshops and has been K-18 Technical Committee Chair of ASME HTD since 2009.

Distributed Heat Conversion Technologies Based on Organic-Fluid Cycles for a High-Efficiency and Sustainable Energy Future

July 15, 2014 08:00

Abstract: The recent heightened involvement in the energy debate, in the scientific community, government and policy circles, and the public domain, has given rise to an intensified interest and rapid developments in a variety of fuel-to-power and heat-to-power conversion technologies. These technological developments have come from all of the areas of energy supply, conversion, storage and provision, spanning a range of scales and diverse applications. In particular, two important aspects of the energy challenge concern: (i) the improved utilisation of the vast amount of rejected energy to the environment, in particular in the form of waste heat from domestic and commercial settings and from a wide range of industrial processes, as well as (ii) the harnessing of renewable and sustainable energy sources, such as the solar resource, for the provision of heat and power, and also, depending on the application, cooling. The widespread deployment of any successful solution to this challenge must be associated with, beyond a high technical performance, either a cost benefit or at the very least a cost that is affordable and economically justifiable to the end-user.

A series of technologies are being proposed that aim to respond to the energy challenge. This paper presents and discusses the emergence of two distinct classes of energy conversion systems based on thermodynamic vapour-phase heat engine cycles undergone by organic working fluids, namely organic Rankine cycles (ORCs) and two-phase thermofluidic oscillators (TFOs). Each type of system has its own distinctive characteristics, advantages and limitations. ORCs are a more well-established and mature technology, are more efficient, especially with higher temperature heat sources and at larger scales, whereas TFOs have the potential to be more cost-competitive, in particular at lower temperatures and at smaller scales. Specifically, ORC systems are particularly well-suited to the conversion of low- to medium-grade heat (i.e. hot temperatures up to about 300 - 400 °C) to mechanical or electrical work, and at an output power scale from a few kW up to 10s of MW. Thermal efficiencies in excess of 25% are achievable at the higher temperatures, and efforts are currently in progress to develop improved ORC systems by focussing on advanced architectures, working fluid selection, heat exchangers and expansion machines. Correspondingly, TFO systems are a more recent development aimed at the affordable conversion of low-grade heat (i.e. hot temperatures from 20 - 30 °C above ambient, up to about 100 - 200 °C) to hydraulic work for fluid pumping and/or pressurisation. Ultimately, TFOs could emerge at scales of up to a few hundred W and with a thermal efficiency of the order of a few % points.

The two energy conversion systems are complementary, and together have a great potential to be used for distributed power generation and improved energy efficiency, leading to primary energy (i.e. fuel) use and emission minimisation. Relevant applications and fields of use include the recovery of waste heat and conversion to useful work including mechanical, hydraulic or electrical energy, or the effective utilisation of renewable energy sources such as geothermal, biomass/biogas and solar energy. In both cases, models capable of accurate and reliable predictions of system performance are used to provide insight on operational characteristics and performance. In particular, the minimisation of thermodynamic losses inflicted by finite heat transfer effects is considered. It is shown that these losses can arise from inherently unsteady, conjugate and nonlinear thermal processes between the working fluids within the systems of interest and the solid walls of key system components. This forms an interesting and important avenue for further work.

Bio: Christos Markides is the Head of the Clean Energy Process (CEP) Laboratory at the Department of Chemical Engineering at Imperial College London. After graduating with a BA (First Class), MEng (Distinction), MA and PhD in Energy Technologies from the University of Cambridge in 2005, he co-founded a spin-out to develop and commercialise a novel thermally-powered fluid-pumping device without mechanical moving parts capable of converting low-temperature heat. He was appointed at Imperial College in 2008. His current research interests focus on the application of fundamental principles of thermodynamics, fluid mechanics, and heat and mass transport to innovative, high-performance heat exchange systems, renewable energy technologies and thermodynamic systems for energy conversion, integration and storage, with emphasis on the efficient utilisation of solar and waste heat. He also has an on-going interest in advanced diagnostics as applied to multiphase, turbulent and reacting flows.

Thermal and Fluid Dynamic Processes Occurring At Liquid Boiling Over Micro-And-Nano Enhanced Surfaces

July 15, 2014 08:00

Abstract: Several strategies for surface modification have been addressed within the last decades to enhance heat transfer between liquids and solid surfaces, particularly involving phase transitions. The fast advance of micro-and-nano technologies provided the researchers with a wide range of solutions to modify the topology and even the chemistry of the surfaces (e.g. micro-patterning, nano-structuring, coating, nanowires and microporous). Alternative solutions comprise the modification of the liquid properties by the addition of surfactants or nanoparticles. The main goal is usually to increase the heat transfer coefficient and/or, in the particular case of pool boiling systems, increase the upper limit imposed by the Critical Heat Flux. However, many researchers focused mainly on the application of the surface modification technologies to achieve their goal, in a trial and error process, leaving the understanding of the physics governing the energy and mass transport phenomena to a secondary role. This is particularly evident when one tries to describe the effect of surface topology and wettability. Despite there is a known, although complex relation between these two factors, many studies do not account for such relation in the analysis of the results. Also, these effects are often mixed up and even misinterpreted. Hence, although the theory dealing with heat and mass transfer at liquid-solid interfaces, has been extensively explored, particularly in pool boiling systems, there are still many issues to solve related to the accurate description of the effect of surface properties. In this context, this talk will revise the effect of the surface properties on the fluid dynamics and heat transfer processes occurring at liquid-solid interfaces, with transition of the liquid phase. Emphasis is given to the heat transfer and bubble dynamics phenomena occurring in pool boiling, although other systems such as droplet/surface interfaces will be considered, particularly for the introduction of wettability concepts. To overcome the historical aforementioned empiricism related with the evaluation of the pool boiling heat transfer on modified surfaces, an alternative approach is suggested to the definition of a theoretical model. This model takes into account the different parcels of heat flux associated with the boiling process and their relation with bubble dynamics and interaction mechanisms. The independent data required for bubble nucleation and heat transfer characterization are collected coupling high speed camera visualization, PIV (Particle Image Velocimetry) and heat flux/surface temperature measurements. Some case study applications are then exploited, mainly related to electronics cooling, thus using dielectric fluids.

Bio: Post-Doc Researcher at the Laboratory of Thermofluids, Combustion and Energy Systems of IN+ - Center for Innovation, Technology and Policy Research, in Instituto Superior Técnico. PhD (2009) – Mechanical Engineering in Instituto Superior Técnico (Lisbon-Portugal). MSc (2004) - Mechanical Engineering (Energy) in Instituto Superior Técnico (Lisbon-Portugal). Mechanical Engineering Degree - 5year course (2001) in Instituto Superior Técnico (Lisbon, Portugal). In 2010 she got a contract from the National Research Foundation to develop a scientific program, for a period of six years, at Instituto Superior Técnico, in collaboration with the University of Sttugart and with the University of Bergamo, under the topic” Integrated strategies to control the transport phenomena in liquid-solid interfaces”. She earned an Honorable Mention in the Young Scientists Awards for the year of 2009 and the 1st Prize in the same awards for the year of 2010. The work developed during the Post-Doc and throughout a significant part of her PhD addressed the characterization of the effects of patterned surfaces on the hydrodynamic and thermal behaviour of liquid droplets and liquid films interacting with heated substrates. Outcomes of her work have been mostly explored for cooling applications, although recent collaborations with Biomedical and Biological Engineering have extended research applications to Biomimetics and sample transport in Biomedical Engineering.

Fundamental Issues in Nanoscale Heat Transfer: From Phonon Coherence in Heat Conduction to Acoustic Based Near-Field Radiation

July 15, 2014 09:20

Abstract: When system sizes shrink to nanoscales as in the case of electronic and optical devices, heat transfer laws are altered due to the modification of the basic physical mechanisms at play, especially in the fields of conduction and radiation. We first expose recent advances in the understanding of heat conduction in semi-conductor superlattices and carbone based systems. The effect of (i) coherence and (ii) interfaces/surfaces becoming predominant, we use a direct simulation technique -i.e. Molecular Dynamics- to estimate the thermal resistance generated by those effects. A mode analysis is also implemented to understand the contributions of coherence, scattering and to reveal the microscopic definition of a Kapitza resistance. We secondly tackle the mechanism of radiation at small scales. When the gap distance between two emitting bodies decreases below the Wien's photon wavelength, direct electrostatic interactions between charges yield an exalted heat transfer larger than the one predicted by Stefan's Law. This so-called "near-field" radiation has been extensively studied in the frame of Maxwell equations by considering dipole-dipole interactions. We show that this approach remains limited to gaps larger than about 10nm and we highlight that charge-charge interactions predominate below this distance down to a few Angstroëms. Below this latter limit, we also prove that Maxwell equations fail because charges have to be described by Schrödinger equations as atoms share electrons. This is the transition between radiation and heat conduction. Those elements provide key tools to design today's thermal interface materials and nanoscale cooling strategies.

Jet in Crossflow: Experiments on the Interaction of Flowstructure and Cooling Efficiency

July 15, 2014 09:20

Abstract: Film-cooling is one of the major techniques used in the protection of materials in gasturbines. Better cooling allows higher gas temperatures which leads to a better engine performance. The drilling of the nozzles can generate imperfections of the geometry, which (due the small size of the nozzles) can lead to imperfection size up to 25% of the nozzle diameter. In this paper, an study will be presented of experiments performed in an appropriately-scaled water channel. Measurements are performed using laser induced fluoresce, particle image velocimetry and thermo-chromic liquid crystal sheets. Different shapes (square, triangular and round) and size (5-25% blockage) of imperfections are used to investigate the role of the nozzle geometry at different velocity ratios (0.15-1.50) with a fixed nozzle angle (37o). As a reference, experiments are conducted with a "perfect" (without any artificial imperfection) hole. Four major coherent structures are found: a counter-rotating vortex pair (in the core of the jet), windward, leeward and spiral (at the hole sides) vortices. Large enough imperfections close to the nozzle exit induce instability in these vertical structures, mainly forcing the counter-rotating vortex pair to oscillate and remain closer to the wall. Since this reduces the exchange of momentum and heat between the jet and the main-stream fluid, the heat-transfer experiments show an increase in cooling effectiveness. When the imperfections are positioned further down in the hole, the lee- and windward vortices grow, which leads to breakdown of the jet. The resulting bursting mechanism lifts the cooled volume and leads to a decrease of the cooling efficiency. Overall this means that the position, size and shape of the geometry disturbance are determining factors in the resulting cooling effectiveness. In some case, the imperfect holes lead to a significantly improved performance, while in some other cases they deteriorate it.

Study of Unsteady Combustion Processes Controlled by Detailed Chemical Kinetics

July 16, 2014 08:00

Abstract: Our understanding of the fundamentals of combustion processes to a large extent was heavily based on the use of a fairly simplified one-step Arrhenius kinetics model. However, the chemical mechanisms are an important factor significantly influencing the processes. The range of validity of simplified chemical schemes is necessarily very limited. Furthermore, it became clear that the use of a one-step Arrhenius model may lead to only a very basic picture describing qualitatively a few major properties of the combustion phenomena with some poor accuracy if any, often rendering misinterpretation of a variety of combustion phenomena. Moreover, many important features of combustion can not be explained without account of the reactions chain nature. An accurate description of unsteady, transient combustion processes controlled by chemical kinetics requires knowledge of the detailed reaction mechanisms for correctly reproducing combustion parameters in a wide range of pressures and temperatures. The availability of such models is essential for gaining scientific insight into the most fundamental combustion phenomena and it is an essential factor for design of efficient and reliable engines and for controlling emissions. In this lecture we consider the option of a reliable reduced chemical kinetic model for the proper understanding and interpretation of the unsteady combustion processes using hydrogen-oxygen combustion as a quintessential example of chain mechanisms in chemical kinetics. Specific topics cover several of the most fundamental combustion phenomena including: the regimes of combustion wave initiated by initial temperature non-uniformity; ignition of combustion regimes by the localized transient energy deposition; the spontaneous flame acceleration in tubes with no-slip walls; and the transition from slow combustion to detonation.

Bio: Mikhail (Misha) A. Liberman is a theoretical physicist born in Moscow, USSR (Russia). After having received his master degree from Moscow State University, in 1966, he received his Ph.D. in 1970 at Lebedev's Institute of General Physics, Moscow, thesis: “Symmetry groups in quantum mechanics”. From 1971 Liberman was invited to the Institute for Physical Problems, Moscow, Russia, where he worked at the Landau Theoretical Department of till 2003. He received his Doctor of Physical and Mathematical Sciences degree in 1981 at A. Budker Institute of Nuclear Physics; thesis: “Nonlinear phenomena and shock waves in plasma”. His many years association with Ya. B. Zeldovich was of particular importance, and Liberman regarded himself as a pupil of Zeldovich. In 1993 Liberman became a professor of Theoretical Physics at Uppsala University, Sweden. He is currently a professor at Nordic Institute for Theoretical Physics (Nordita), Sweden, Professor Emeritus at the Uppsala University and honorary professor of Moscow Institute of Physics and Technology, Russia. He was elected a fellow of American Physical Society: “For outstanding contributions ranging from laboratory plasma experiments to astrophysical phenomena, particularly in the areas of shock waves, Z-pinches, flame stability, and laser produced plasmas.” Liberman made fundamental contributions to many areas of theoretical physics, including physics of shock wave, plasma physics, quantum theory and combustion. His accomplishments include the theory of dynamics and stability of Z-pinches and plasma liners, which also resulted in the development of a new method for production of ultrahigh magnetic field. In collaboration with Sandia National Laboratories a world record pulsed magnetic field of 43MG has been obtained experimentally. In quantum mechanics Liberman obtained an exact analytical solution for a hydrogen atom in a magnetic field of arbitrary strength; and for hydrogen molecule in ultrahigh magnetic fields; developed theory of the Bose condensate of excitons in semiconductors in a high magnetic field and in a low-dimensional systems. He is best known as one of the world's leading scientists in combustion theory. Liberman's major contributions in combustion theory include a comprehensive theory of dynamics and stability of laminar flame and fractal structure of a spherically expanding flame; interaction of flames with acoustic and shock waves; a nonlinear equation for a nonperturbative description of curved premixed flame with arbitrary gas expansion subject to the hydrodynamic instability and its analytical solutions have been obtained (with Kazakov). For the first time in his work the origin and the physical mechanism of the transition from slow combustion (deflagration) to detonation regime was explained. Liberman's recent research is focused on study of key combustion problems with account a detailed chemical kinetics, which led to qualitative and quantitative revision of the combustion fundamentals. Liberman has authored/co-authored the books: Physics of Shock Waves in Gases and Plasmas, Springer-Verlag, 1985 (with A. Velikovich), Physics of High-Density Z-pinch Plasmas, Springer-Verlag, 1998 (with J.DeGroot, A.Toor, R.Spielman), Introduction to Physics and Chemistry of Combustion, Springer-Verlag, 2008. He has authored/co-authored over 300 peer-reviewed papers.

Role of Energy and Exergy Analyses in Performance Improvement and Development of Advanced and Sustainable Energy Systems

July 16, 2014 08:00

Abstract: The energy demand is growing and this has to be met with reduced pollutants and greenhouse gas emissions. Apart from natural gas and coal energy systems, alternative energy sources are receiving a great deal of attention in recent years for power generation. The presentation will discuss natural gas, coal, biomass, solar power generation and hybrid power generation systems. The role of thermodynamics (energy and exergy analyses) in the analysis and performance improvement of natural gas, coal and biomass advanced and integrated energy systems will be discussed. Biomass power systems, biomass co-firing hybrid power generation systems are also receiving attention to reduce greenhouse emissions. The biomass power generation systems and the recent developments in biomass hybrid power generation systems will also be presented. The presentation will also focus on integrated and multi-generation systems. The exergy analysis for power generation systems is also receiving attention due to the ability to analyze a power generation system on a component basis and also as a whole system from quality point of view. The exergy analysis for natural gas, coal and biomass power generation systems and its role on plant performance will be discussed.

Bio: Dr. Bale V. Reddy is a Professor in Department of Mechanical Engineering in Faculty of Engineering and Applied Science, University of Ontario Institute of Technology (UOIT), Oshawa, Ontario, Canada. Prior to this, Dr. Reddy also worked as an Associate Professor in Mechanical Engineering Department, University of New Brunswick (UNB), Fredericton, Canada. Dr. Reddy received his MTech and PhD degrees in Mechanical Engineering from IIT, Kharagpur, India. Dr. Reddy research interests are in the area of natural gas and coal advanced energy systems, biomass, gasification, exergy analysis, solar energy, energy management and waste heat recovery. Dr. Reddy has led funded research projects in the area of fluidized bed combustion, natural gas and coal energy systems, biomass, energy efficiency improvement and biofuels. He has also supervised/co-supervised graduate and under graduate project/design thesis students, research assistants and postdoctoral fellows. Dr. Reddy has published so far 185 papers in refereed international journals and refereed conference proceedings. Dr. Reddy has delivered keynote and invited presentations in many international conferences. He has also chaired technical sessions in various international conferences. He has also delivered invited seminar presentations in various universities. Dr. Reddy is involved in the organization of conferences in heat transfer, thermal, energy and mechanical engineering areas as a conference chair, organizing chair, organizing committee member etc. He is also involved in the ASME Energy Sustainability Conferences as a track chair. As an organizing committee member, he is involved in Global Conference on Global Warming conference organization. He is also involved as an organizing/advisory committee member and coordinating scientist in many international conferences. Dr. Reddy also contributed ten book chapters along with his research collaborators and students in the area of thermodynamics and energy systems area. Dr. Reddy has also received best professor award for teaching excellence five times both in India (VIT, Vellore) and in Canada (UNB, Fredericton; UOIT, Oshawa).

Can We Obtain First Principle Results for Turbulence Statistics?

July 16, 2014 09:20

Abstract: Text-book knowledge proclaims that Lie symmetries such as Galilean transformation lie at the heart of fluid dynamics. These important properties also carry over to the statistical description of turbulence, i.e. to the Reynolds stress transport equations and its generalization, the multi-point correlation equations (MPCE). Interesting enough, the MPCE admit a much larger set of symmetries, in fact infinite dimensional, subsequently named statistical symmetries.

Most important, theses new symmetries have important consequences for our understanding of turbulent scaling laws. The symmetries form the essential foundation to construct exact solutions to the infinite set of MPCE, which in turn are identified as classical and new turbulent scaling laws. Examples on various classical and new shear flow scaling laws including higher order moments will be presented. Even new scaling have been forecasted from these symmetries and in turn validated by DNS.

Turbulence modellers have implicitly recognized at least one of the statistical symmetries as this is the basis for the usual log-law which has been employed for calibrating essentially all engineering turbulence models. An obvious conclusion is to generally make turbulence models consistent with the new statistical symmetries.

Bio: Martin Oberlack is Professor of Mechanical Engineering at Darmstadt University and holder of the chair for fluid dynamics. He received his Bachelors degree in Mechanical Engineering from the University of Essen in 1985. His Diploma degree he obtained in 1988, his Ph.D. degrees in 1994 and his Habilitation in 2000 all from the RWTH Aachen. He joined the TU Darmstadt faculty of Civil Engineering in September 2000. After various external offers, which he declined, he changed to the Department of Theoretical and Applied Mechanics in 2005 and one year later he switched to the Department of Mechanical Engineering. He co-founded the Center of Smart Interfaces and the Graduate School of Excellence Computational Engineering at Darmstadt University. He has been actively involved in the editorial boards of the Theoretical and Computational Fluid Dynamics, Fluid Dynamic Research, Continuum Mechanics and Thermodynamics and is presently co-editor of the book Series “Mathematical Physics: Theory and Applications” of Atlantis Press/Springer publisher. He refereeing activities include almost forty international journals and ten international funding organizations. Prof. Oberlack pioneered the use of Lie symmetry methods for the study of turbulence physics and statistics, combustion and modelling concepts and has written widely on this with a special focus on turbulent shear flows. His current interests include: Lie symmetries of the Lundgren-PDF and Hopf equation of turbulence, construction of conservation laws, hydrodynamic stability theory, multi-phase flows, aerodynamic noise, combustion, high-performance and parallel computing, GPU acceleration, Discontinuous Galerkin numerical methods with special focus on singular problems such as multi-phase flows and large scale direct turbulence simulations. Already for this Habilitation thesis in 2000, in which he laid the foundation for the symmetry based turbulence theory, he was awarded the Friedrich-Wilhelm Award of RWTH Aachen and the Academy Award of the North Rhine-Westphalia Academy of Sciences and he received the Hermann-Reissner-Award of the Dept. of Aero- and Astronautics of the University of Stuttgart for his Contributions in Turbulence Research. Recently he was awarded the Athene Best Teaching Award of the Department of Mechanical Engineering as well as the E-Teaching-Award of TU Darmstadt for the innovative development of electronic media in teaching. Prof. Oberlack is a member of the American Physical Society, the German Committee for Mechanics, the International Association of Applied Mathematics and Mechanics, the European Mechanics Society and the European Research Community on Flow, Turbulence and Combustion.

MAAT System Design - Weight Model of Very Large Lighter-Than-Air Vehicle

July 16, 2014 09:20

Abstract: The main objective of this paper is to provide a realistic weight model, based on the physical-mathematical foundations, for the design of the new very large lighter-than-air vehicle, called Multibody Advanced Airship for Transport (MAAT), the ongoing European FP7 project under intensive research and development activities. The Modeling and Simulation (M&S) principles, aided with simulations and visualization tools, have been extensively used, as the key enablers to combine, manage and structure such highly complex engineering process, which emerged as a natural integration mechanism and evidence provider of the encountered complexity, successfully encompassing the MAAT multidisciplinary design requirements. The authors experience, in solving the M&S problems, gained within the European R&D projects, was efficiently reused, where the use of such software technologies have been successfully demonstrated, and today, further applied for the new generation transportations solutions, as envisaged by MAAT, especially addressing the best practices in taking advantage of the variety of multi-physics software and their related analysis tools. The MAAT system is envisaged to be composed of two airships: the Cruiser, which stays at a constant altitude of 16 km, travelling horizontally; and the Feeder, which acts like an elevator system connecting the Cruiser to the ground. In this paper, the proposed weight model is similar to the typical one applied in the aircraft design process. The main difference is primarily the airship teardrop shape, which is commonly applied for the currently produced airships. The main challenge is that MAAT has a very large shape, which has required the introduction of new elements and references, as being presented in this work. The achieved results show that MAAT can be realized, by taking into account the significant weight estimated for such aircrafts, to be for the Cruiser about 533 tons, while the Feeder weight is about 12 tons. As highlighted before, the MAAT design is still under intensive developments, and thus, it is expected that in the coming years, by taking into account the new emerging technological solutions, the lightening of such aircrafts structure is inevitable. In addition, the authors plans are to further investigate new materials and their related applications, in order to improve the structural part of the MAAT system, as one of the essential parts in such new transportation system, expected to become the reality in the forthcoming future.

Bio: Prof. Dr. Ir. Dean Vučinić joined Vesalius College (VeCo) affiliated to the Vrije Universiteit Brussel (VUB) in 2017. He is affiliated to VUB since 1988, before VeCo, member of Mechanical Engineering (MECH) and Electronics & Informatics (ETRO). Part-time associate professor at the Faculty of Electrical Engineering, Computer Science and Information Technology (FERIT), University of Osijek. Interested in Scientific Visualization, Modelling and Simulation, Optimization, Software Engineering and HPC-ExaScale. Participated in more than 20 European projects (EC Frameworks, EUREKA/ITEA and Tempus/Erasmus+). Member of International Advisory Boards and Scientific Committees of Journals and Conferences, acting as chair, session organizer, reviewer and editor. European Commission expert in H2020 and member of international organizations: AIAA, IEEE, ACM, SAE & ASME.