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13th International Conference on Liquid Atomization and Spray Systems, ICLASS 2015

作者： Fritsching, U. Lampa, A. Particles and Process Engineering University of Bremen Germany

Preferential concentration and clustering influences the heat and mass transfer for spray droplets. The effect of droplet clustering is of interest for many spray applications, e.g. in automotive spray combustion. In this paper the meso-scale droplet clustering in sprays is investigated. Droplet clustering here is mainly caused by the droplet interaction with eddy structures in the gas flow. In order to simulate the vortex formations in the gas flow the Large-Eddy-Simulation (LES) approach has been used. The heat transfer between the droplets and the gas is analysed with respect to local concentration inhomogeneities. The results of this study indicate that the effect of the spatial inhomogeneity of the droplet concentration on the heat transfer in cluster is of importance in areas of local Stokes regimes slightly larger than unity. The resulting cluster structures on the spray axis are long-living and their formation process is a non-spontaneous. The results of the numerical simulation are compared with Particle-Image-Velocimetry measurements. The spray morphology, namely the droplet clusters, as well as statistical values of the flow variables for the dispersed phase agree well in experiment and simulation. © 2015 International Conference on Liquid Atomization and Spray Systems. All rights reserved.

关键词： Large eddy simulation

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A high-speed process monitoring system to detect and analyze filaments and droplet collisions in spray processes in real time 13

A high-speed process monitoring system to detect and analyze...

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13th International Conference on Liquid Atomization and Spray Systems, ICLASS 2015

作者： Klaiber, M. Guhathakurta, J. Li, W. Wang, Z. Lampa, A. Li, H. Simon, S. Sommerfeld, M. Fritsching, U. Institute of Parallel and Distributed Systems University of Stuttgart Germany Institute of Particles and Process Engineering University of Bremen Germany Institute of Mechanical Process Engineering Martin Luther University of Halle-Wittenberg Germany

In this paper a novel optical high-speed Real-Time process Monitoring System is proposed and used to measure spray and atomization processes. It captures images in high speed and the build-in hardware architecture for image processing is designed to evaluate statistics of dispersed objects in the spray. Thus, it represents an online process measuring tool of the next generation for optical analysis. Features of droplets, particles, ligaments and filaments, such as the size or circularity, are extracted. A novelty is the feature to detect distinctive events online and in real-time. This automatic extraction of time-series of images requires only a low amount of data to be evaluated offline. An application is demonstrated in the context of droplet collisions and filament formation. The Real-Time process Monitoring System provides statistics on the spray which is used to distinguish between spherical droplets, ligaments and filament networks. The high-speed features extraction of object information can be used for an automatic control loop for optimizing the spray process properties. © 2015 International Conference on Liquid Atomization and Spray Systems. All rights reserved.

关键词： Image processing

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Numerical derivation of forces on particles and agglomerates in a resonant acoustic field

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AIP Conference Proceedings 2013年第1期1558卷 1115-1118页

作者： Claas Knoop Udo Fritsching Particles and Process Engineering University Bremen Badgasteiner Straße 3 D-28359 Bremen Germany

particles and agglomerates are investigated in gaseous acoustic flow fields. Acoustic fields exert forces on solid objects, which can influence the shape of the exposed bodies, even to the point of breakage of the structures. Motivated by experimentally observed breakage of agglomerates in an acoustic levitator (f = 20 kHz), a numerical study is presented that derives the acoustic forces on a complex model agglomerate from the pressure and velocity fields of a resonant standing ultrasound wave, calculated by computational fluid dynamics (CFD). It is distinguished between the drag and lift/lateral forces on the overall agglomerate and on the different primary particles of the model.

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Controlled quenching of aluminum specimen in flexible spray fields for the reduction of distortion

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6th International Quenching and Control of Distortion Conference: Quenching Control and Distortion, Including the 4th International Distortion engineering Conference

作者： Hornig, Nils Fritsching, Udo Rose, Andrea Schuettenberg, Sven Von Hehl, Axel University of Bremen Particles and Process Engineering Badgasteiner Str. 3 Bremen PA 28359 Germany IWT Stiftung Institut für Werkstofftechnik Badgasteiner Str. 3 Bremen PA 28359 Germany

ISBN: (纸本)1615039805

During heat treatment of age hardenable aluminum alloys, the resulting mechanical properties can particularly be influenced by the quenching process. To achieve a required strength, a high efficient cooling rate after solution annealing is necessary. In order to avoid distortion, a homogeneous distribution of quenching intensity should be realized as well. Controlled quenching within heat treatment processes of aluminum components can be realized by flexible jet and spray fields. Suitable heat transfer conditions of the aluminum components are realized by adjusted flexible flow fields (local and/or temporal) based on quenching simulations by Computational Fluid Dynamic methods (CFD). By the use of gas-(air), spray-(water/air) or jet-(water) flow fields, it is possible to adapt the quenching intensity to the component geometry, thereby controlling the mechanical properties as well as the distortion after heat treatment. The controlled quenching with aqueous media, especially the use of multiphase atomizers for spray cooling processes, offer the possibility for generating specific local heat transfer conditions and therefore achieving results of controlled asymmetric quenching on components to reduce distortion. For this purpose, a flexible spray field quenching process was integrated into the heat treatment for age hardening of different wrought-, cast-, and spray formed aluminum alloys. In this contribution, the process outline for spray quenching of aluminum specimen will be introduced. Results for aluminum specimen quenched in flexible spray fields will be discussed. The effect of quenching process parameters of the aqueous and air phase on the aluminum specimen will be determined through hardness measurements and tensile tests. Furthermore, the temperature profiles of asymmetrically quenched specimen through the usage of flexible nozzle fields will be discussed. Infrared thermography was performed on aluminum specimen to provide experimental data for the implemen

关键词： Quenching

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Numerical investigation of binary droplet collisions in all relevant collision regimes

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Journal of Computational Multiphase Flows 2011年第4期3卷 207-224页

作者： Li, Xing Fritsching, Udo Particles and Process Engineering Department University of Bremen Badgasteiner Str. 3 D-28359 Bremen Germany

A numerical investigation of binary droplet collisions in a gaseous phase has been conducted. A volume of fluid (VOF) based interface capturing method, which is characterized by introducing an extra artificial compression term into the volume-fraction transport equation, is employed to capture the liquid-gas interface. The full Navier-Stokes equations coupled with the volume-fraction transport equation are discretized on a fixed, uniform grid using the finite volume method. The solution of the volume-fraction transport equation is bounded by an explicit universal multidimensional limiter. The simulations cover five major regimes of binary droplet collisions: (I) coalescence with minor deformation, (II) bouncing, (III) coalescence with major deformation, (IV) reflexive separation and (V) stretching separation. A ghost cell method is introduced in order to simulate bouncing and retarded coalescence in head-on collisions. Especially, for retarded coalescence collisions, the volumefraction boundary condition on the symmetry plane is switched to numerically control coalescence at a critical time which is determined by tracking the interface front. The simulated results are compared with the attainable experimental data and provide detailed pictures exhibiting the droplet collision processes. The inter-droplet pressure, defined by the static pressure on the symmetry plane in head-on collisions, is also evaluated and analyzed.

关键词： Deformation

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Turbulence and little rip cosmology

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Physical Review D 2012年第6期86卷 063007-063007页

作者： I. Brevik R. Myrzakulov S. Nojiri S. D. Odintsov Department of Energy and Process Engineering Norwegian University of Science and Technology N-7491 Trondheim Norway Eurasian International Center for Theoretical Physics and Department of General & Theoretical Physics Eurasian National University Astana 010008 Kazakhstan Department of Physics Nagoya University Nagoya 464-8602 Japan Kobayashi-Maskawa Institute for the Origin of Particles and the Universe Nagoya University Nagoya 464-8602 Japan Consejo Superior de Investigaciones Científicas ICE/CSIC-IEEC Campus UAB Facultat de Ciències Torre C5-Parell-2a pl E-08193 Bellaterra (Barcelona) Spain Institució Catalana de Recerca i Estudis Avançats (ICREA) 08010 Barcelona Spain Tomsk State Pedagogical University Tomsk 634061 Russia

A variety of conditions are considered under which the cosmic dark fluid may be able to develop a future Big Rip or Little Rip singularity. Both one-component and two-component models are considered. In the latter case we present a way in which the fluid can be decomposed into two components, one nonturbulent (ideal) and one turbulent part, obeying two different equations of state. For the nonturbulent part, the thermodynamical parameter, commonly called w, is assumed to be less than −1 throughout. For the turbulent part, it turns out that it is sufficient that wturb lies in the quintessence region in order to lead to a singularity. Both Big Rip and Little Rip behavior for dark energy are found. In the one-component case, we examine how the universe may develop from a viscous era with constant bulk viscosity into a turbulent era, the turbulence in effect protecting the universe from encountering the singularity at all. The equivalent description of the same cosmology in terms of inhomogeneous (imperfect) fluid is also presented.

关键词： COSMOLOGY NUCLEAR models TURBULENCE DARK matter (Astronomy) THERMODYNAMICS EQUATIONS of state FLUIDS

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Viscous little rip cosmology

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Physical Review D 2011年第10期84卷 103508-103508页

作者： I. Brevik E. Elizalde S. Nojiri S. D. Odintsov Department of Energy and Process Engineering Norwegian University of Science and Technology N-7491 Trondheim Norway Consejo Superior de Investigaciones Científicas ICE/CSIC-IEEC Campus UAB Facultat de Ciències Torre C5-Parell-2a pl E-08193 Bellaterra (Barcelona) Spain Department of Physics Nagoya University Nagoya 464-8602 Japan Kobayashi-Maskawa Institute for the Origin of Particles and the Universe Nagoya University Nagoya 464-8602 Japan Institució Catalana de Recerca i Estudis Avançats (ICREA) Tomsk State Pedagogical University

Dark energy of phantom or quintessence nature with an equation of state parameter w almost equal to −1 often leads the universe evolution to a finite-time future singularity. An elegant solution to this problem has been recently proposed [P. H. Frampton, K. J. Ludwick, and R. J. Scherrer, Phys. Rev. D 84, 063003 (2011).] under the form of the so-called little rip cosmology, which appears to be a realistic alternative to the ΛCDM model. A viscous little rip cosmology is here proposed. Whereas generically bulk viscosity tends to promote the big rip, we find that there are a number of situations where this is not the case and where the formalism nicely adjusts itself to the little rip scenario. We prove, in particular, that a viscous fluid (or, equivalently, one with an inhomogeneous [imperfect] equation of state) is perfectly able to produce a little rip cosmology as a purely viscosity effect. The possibility of its induction as a combined result of viscosity and a general (powerlike) equation of state is also investigated in detail. To finish, a physical, inertial force interpretation of the dissolution of bound structures in the little rip cosmology is presented.

关键词： DARK energy (Astronomy) COSMOLOGY VISCOSITY FORCE & energy HYDRODYNAMICS

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Transition Metal-Doped Lithium Titanium Oxide Nanoparticles Made Using Flame Spray Pyrolysis

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International Scholarly Research Notices 2011年第1期2011卷

作者： T. Karhunen A. Lähde J. Leskinen R. Büchel O. Waser U. Tapper J. Jokiniemi Fine Particle and Aerosol Technology Laboratory Department of Environmental Science University of Eastern Finland 70211 Kuopio Finlanduef.fi Particle Technology Laboratory Department of Mechanical and Process Engineering ETH Zürich 8092 Zürich Switzerlandethz.ch Fine Particles VTT Technical Research Centre of Finland 02044 VTT Finlandvtt.fi

Defect spinel phase lithium titanate (Li 4 Ti 5 O 12 ) has been suggested as a promising negative electrode material for next generation lithium ion batteries. However, it suffers from low electrical conductivity. To overcome this problem conduction path length can be reduced by decreasing the primary particle size. Alternatively the bulk conductivity of Li 4 Ti 5 O 12 can be increased by doping it with a conductive additive. In this paper a steady, single-step gas-phase technique for lithium titanate synthesis that combines both approaches is described. The process is used to produce doped Li 4 Ti 5 O 12 nanoparticles with primary particle size of only 10 nm. The product is found to consist of single-crystalline nanoparticles with high phase and elemental purity. Two dopant materials are tested and found to behave very differently. The silver dopant forms a separate phase of nanometre-sized particles of metallic silver which agglomerate with Li 4 Ti 5 O 12 . The copper dopant, on the other hand, reacts with the lithium titanate to form a double spinel phase of Li 3 (Li 1−2 x Cu 3 x Ti 5− x )O 12 .

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Pilot Study on Drinking Water Advanced Treatment by GAC-MF System

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Journal of Donghua University(English Edition) 2004年第1期21卷 135-139页

作者：王欣泽薛罡王宝贞王琳 School of Environmental Science and Engineering Shanghai Jiaotong University Shanghai 200240 School of Municipal & Enviromnental Engineering Harbin Institute of Technology Harbin 150090 College of Environmental Science and Engineering Donghua University Shanghai 200051 School of Municipal & Enviromnental Engineering Harbin Institute of Technology Harbin 150090 School of Municipal & Enviromnental Engineering Harbin Institute of Technology Harbin 150090he pilot performance of the combined GAC-MF membrane process for drinking water advanced treatment was described. In the process of GAC adsorption under the conditions of 20 min HRT and 6 m/h filtration rate the removal efficiencies of UV_(254) and trichloromethane could reach 40% and 50% respectively and the UV_(254) and trichloromethane in system effluent was less than 0.015 cm~(-1) and 5μg/L respectively. In the post MF membrane process MF membrane effectively retained the particles and bacteria in raw water. The effluent turbidity was less than 0.2 NTU and no bacteria were detected at all in permeate. A computer-controlled system was employed to control this system. The membrane operating parameters of backwash interval duration and flux were studied. The backwash interval of 10-min 20-min and 60-min was researched respectively and the variation of trans-membrane pressure was also analyzed. Consequently short backwash interval was recommended under the same water consume.

The pilot performance of the combined GAC-MF membrane process for drinking water advanced treatment was described. In the process of GAC adsorption, under the conditions of 20 min HRT and 6 m/h filtration rate, the removal efficiencies of UV_(254) and trichloromethane could reach 40% and 50% respectively and the UV_(254) and trichloromethane in system effluent was less than 0.015 cm^(-1) and 5μg/L respectively. In the post MF membrane process, MF membrane effectively retained the particles and bacteria in raw water. The effluent turbidity was less than 0.2 NTU and no bacteria were detected at all in permeate. A computer-controlled system was employed to control this system. The membrane operating parameters of backwash interval, duration and flux were studied. The backwash interval of 10-min, 20-min and 60-min was researched respectively, and the variation of trans-membrane pressure was also analyzed. Consequently short backwash interval was recommended under the same water consume.

关键词： granular activated carbon adsorption MF membrane drinking water advanced treatment

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Simulation of the Clustering Phenomenon in a Fast Fluidized Bed: The Importance of Drag Correlation

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Chinese Journal of Chemical engineering 2004年第3期12卷 335-341页

作者：王维李佑楚 Institute of Process Engineering Chinese Academy of Sciences Beijing 100080 China Institute of Process Engineering Chinese Academy of Sciences Beijing 100080 Chinarag force is a key parameter in the numerical modeling of gas-particle flow in circulating fluidized beds. The reliability of current drag force correlations over the regime of fast fluidization has however not been thoroughly investigated. In this article a drag force correlation accounting for the clustering effects for Geldart A particles is used to simulate the behaviors typical of fast fluidization including dynamic evolution of clusters as well as time- averaged axial and lateral voidage profiles. Diverse images of clusters are captured and the time-averaged profiles of voidage are shown to be in quantitative agreement with the present empirical correlation. The results based on different constitutive correlations of drag force show the importance of the choice of drag force in modeling fast-fluidized beds. This drag force correlation based on a simple averaging assumption could give some basic insights about the magnitude of the drag reduction.

Drag force is a key parameter in the numerical modeling of gas-particle flow in circulating fluidized beds. The reliability of current drag force correlations over the regime of fast fluidization has, however, not been thoroughly investigated. In this article, a drag force correlation accounting for the clustering effects for Geldart A particles is used to simulate the behaviors typical of fast fluidization, including dynamic evolution of clusters as well as time- averaged axial and lateral voidage profiles. Diverse images of clusters are captured and the time-averaged profiles of voidage are shown to be in quantitative agreement with the present empirical correlation. The results based on different constitutive correlations of drag force show the importance of the choice of drag force in modeling fast-fluidized beds. This drag force correlation, based on a simple averaging assumption, could give some basic insights about the magnitude of the drag reduction.

关键词： drag force kinetic theory granular materials fast fluidization multiphase flow simulation

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