Publikationen
Publikationen
Forschung ist unsere Leidenschaft
O. Sommer und G. Wozniak: Über die Ausbildung und Form von flüssigen Wülsten an gekrümmten Festkörperkanten. Forschung im Ingenieurwesen. https://doi.org/10.1007/s10010-023-00679-2 (2023)
L. Kille, V. Strohbücker, R. Niesner, O. Sommer und G. Wozniak: Experimental Investigation of Droplet Formation and Droplet Sizes behind a Side Mirror. SAE Technical Paper 2022-01-5107, doi:10.4271/2022-015107 (2022)
E. Tadrous und (and) G. Wozniak: Experiments on the transition of thermocapillary convection towards turbulent flow. Physical Review Fluids 6, 063601 (2021)
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M. Roudini und (and) G. Wozniak: Experimental Investigation of Spray Characteristics of Prefilming Air-blast Atomizers II – Influence of liquid Properties. Journal of Applied Fluid Mechanics, Vol. 13, No. 2, pp. 679-691 (2020)
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J. Emmrich und G. Wozniak: Ein Beitrag zur experimentellen Untersuchung hybrider Filterzyklone für die Partikelabscheidung aus Gasen. Forschung im Ingenieurwesen – Engineering Research, 2015, DOI 10.1007/s10010-015-0192-3
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Heiland, H. G.; Sommer, O.; Wozniak, G.: Experimentell Untersuchung der thermischen Konvektion in einem geneigten Spalt. Forschung im Ingenieurwesen Vol. 76, No. 3-4, 87-95 (2012)
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Heiland, H. G.; Rubes, D.; Wozniak, G.: Convection experiments in an inclined narrow cavity. Heat and Mass Transfer Vol. 48, No. 12, 2007-2012 (2012)
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Heiland, H. G.; Schade, K.-P.; Wozniak, G.: Thermocapillary flow on a gas surface under normal and reduced gravity. Proc. Appl. Math. Mech. Vol. 11, 609-610, (2011)
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H. G. Heiland und G. Wozniak: Application of a novel colour imaging technique to thermal convection under reduced gravity. Meas. Sci. Technol. (2010) 125902 (9pp)
Abstract: The quantitative measurement performance and the robustness of a novel high-speed imaging system using a liquid crystal tunable filter have been verified by a fluid dynamic experiment in a reduced gravity environment. This new type of diagnostic tool is a combination of a monochrome high-speed CCD camera with fast ferroelectric liquid crystal control. The filter can be tuned to red, green and blue colour planes (RGB filter), which provides real colour images without loss of resolution. The scientific application was the investigation of the influence of buoyancy on the surface tension-driven flow around a bubble on heated wall. The flow velocity and temperature patterns were observed in gravity and microgravity environments. The measuring technique is based on particle image velocimetry and thermometry (PIV/T). The principle of this optical full-field technique relies on seeded thermochromic liquid crystals (TLCs) as signal particles, which change colour depending on their temperature. The experimental results of the flow investigations under 1-g and μ-g conditions are discussed and compared with one another.
D. Rubes, H. G. Heiland und G. Wozniak: Experimental Investigation of thermal convection in an inclined narrow gap II. Proc. Appl. Math. Mech. 9, 491-492 (2009)
Abstract:In the past decade the development in micro technology has experienced great progress, what made the knowledge of the flow behavior in small cavities fundamentally interesting. Our experimental contribution describes the measured temperature and velocity fields in a fluid containing inclined cavity with the dimensions 17 x 6 x 24 mm3 (w x d x h). Using PIV/T, we can determine the velocity and temperature distribution in the cavity simultaneously. The chamber is illuminated with a white light sheet of 1 mm. A 20 % glycerin-water mixture is examined. The lower side is heated to 46,2°C, while the upper side has a constant temperature of 26°C. In this work we present the measured velocity and temperature fields of the fluid at different angles of the cavity orientation with respect to the direction of gravity in the stationary state. This is a continuation of last years presentation [1] in the sense that the temperature difference has been substantially increased.
K.-P. Schade, G. Wozniak und D. Rubes: Unstable Thermocapillary Flow at a Gas-Liquid Phase Boundary. Proc. Appl. Math. Mech. 9, 455-456 (2009)
Abstract:We present results of thermocapillary experiments in the vicinity of a bubble under a heated wall. Thermocapillary convection is a flow along the interface of two fluids, which is caused by local gradients of the surface tensions σ.
The aim of the present work is to study this flow phenomenon at higher Marangoni-numbers Mg. At sufficiently high values of Mg the flow exhibits oscillatory fluid motion and eventually becomes turbulent. For the detection of the flow velocity and temperature field, we applied a PIV method and a modified differential interferometer. ln order to separate buoyancy effects from thermocapillary convection, we chose an experimental setup, where a bubble is positioned in a liquid matrix under a heated wall.
We could observe various regimes of Marangoni flow, from steady flow over regular oscillating up to highly irregular oscillating flows at Mg up to 63.000. However, we also found unexpected stable flow regions and additional evaporation processes.
The aim of the present work is to study this flow phenomenon at higher Marangoni-numbers Mg. At sufficiently high values of Mg the flow exhibits oscillatory fluid motion and eventually becomes turbulent. For the detection of the flow velocity and temperature field, we applied a PIV method and a modified differential interferometer. ln order to separate buoyancy effects from thermocapillary convection, we chose an experimental setup, where a bubble is positioned in a liquid matrix under a heated wall.
We could observe various regimes of Marangoni flow, from steady flow over regular oscillating up to highly irregular oscillating flows at Mg up to 63.000. However, we also found unexpected stable flow regions and additional evaporation processes.
J. Wu, D. Rubes, H. G. Heiland und G. Wozniak: Investigation of Thermal Convection in an Inclined Narrow Cavity. Proc. Appl. Math. Mech. 8, 10647-10648 (2008)
Abstract: ln order to adapt to the rapid progress in fabricating and utilizing micro electromechanical systems, the investigation of the fluid behaviour in small volumes is of fundamental importance as far as heat and mass transfer are concerned. After the experimental exploration in a small vertical gap with a temperature gradient [1], subsequently the investigation of thermal convection in an inclined narrow cavity is followed experimentally. The gap volume is 6 x 24 x 17 mm3 with a width of 6 mm. Liquid crystal tracer particles are used for measuring the temperature and velocity distribution of the fluid. The measurement results are presented and discussed.
H. Shalaby, K. Wozniak und G. Wozniak: Numerical calculation of particle-laden flow using LES. Engineering Applications of Computational Fluid Mechanics 2, 4, 382-392 (2008)
Abstract: Numerical flow calculations were carried out at various axial positions of a gas cyclone separator for industrial applications. Due to the nature of cyclone flows, which exhibit highly curved streamlines and anisotropic turbulence, we used the advanced turbulence model of Large Eddy Simulation (LES). The application of LES reveals better agreement with the experimental data, however, it requires higher computer capacity and longer running times when compared to standard turbulence models. These calculations of the continuous phase flow were the basis for modeling the behavior of the solid particles in the cyclone. Particle trajectories, pressure drop and the cyclone separation efficiency have been studied in some details. The paper is organized into five sections. The first section consists of an introduction and a summary of previous work. Section 2 deals with the LES turbulence calculations of the continuous phase flow. The third section treats modeling of the dispersed phase behavior. ln section 4, computational issues are presented and discussed as applied grids, boundary conditions and the solution algorithm. ln section 5, prediction profiles of the gas flow at axial positions are presented and discussed in some details. Moreover, pressure drop, particle trajectories and cyclone efficiency are discussed. Section 6 summarizes V and concludes the paper.
G. Wozniak, K.-P. Schade, K. Wozniak und H. H. Shalaby: Über die Auslegung und den Entwicklungsstand von Zyklon-Abscheidern. Forsch Ingenieurwes 71, 171-180 (2007)
Abstract: Cyclone separators are technically simple and robust devices for the separation of solid or liquid materials from fluids and widely used in industry. Their layout and design is mostly based on empirical calculation methods. However, due to the advancing computer technology numerical flow calculation methods (Computational Fluid Dynamics CFD) are increasingly applied to the design and optimization of particle separators.
In the present paper, standard procedures and novel numerical flow simulation methods for the design of cyclonseparators for industrial purposes are presented and described. We discuss the pros and conts of both methods andgive hints regarding the potential of numerical flow simulation for further improving the separation efficiency.
In the present paper, standard procedures and novel numerical flow simulation methods for the design of cyclonseparators for industrial purposes are presented and described. We discuss the pros and conts of both methods andgive hints regarding the potential of numerical flow simulation for further improving the separation efficiency.
H. G. Heiland, K. Wozniak und G. Wozniak: Experimental investigation of thermal convection in a small vertical gap using liquid crystals. Heat and Mass Transfer 43: 863 – 870 (2007)
Abstract: Abstract Thermal convection in a small vertical gap is studied experimentally applying digital particle image velocimetry/thermometry. This optical method enables the simultaneous measurement of two-dimensional flow and temperature fields in a liquid. The principle is based on seeding the liquid flow medium with thermochromic liquid crystal particles. The temperature is measured by the crystal particles which change their reflected colour as function of temperature. The flow velocity is measured by using the same particles as flow tracers. The investigation shall contribute to the understanding of the fluid mechanical behaviour of biological liquids within micro reactor systems. However, the problem is also of fundamental interest as far as heat and mass transfer is concerned. Measured temperature and fiow velocity fields are presented and discussed.
H. Shalaby, K. Wozniak und G. Wozniak: Particle-Laden Flow Simulation in a Cyclon Separator. Proc. Appl. Math. Mech. 6, 547-548 (2006)
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Wozniak, G., Rubes, D., Wozniak, K., Heiland, H. G.: Konvektionsexperimente mit flüssigkristallinen Tracerteilchen in einem engen vertikalen Spalt. Forsch Ingenieurwes, 70, 221-229, (2006)
Abstract: Thermal convection of a liquid in a small vertical gap is studied experimentally applying the liquid crystal tracer technique. This optical method enables the simultaneous measurement of both flow and temperature field in a liquid. The investigation shall contribute to the understanding of the fluid mechanical behaviour of liquids in small cavities like in micro bioreactor systems. However, the problem is also of fundamental interest as far as heat and mass transfer are concerned. Measured temperature and flow velocity fields of the liquids under investigation are presented and discussed.
Shalaby, H., Pachler, K., Wozniak, K., Wozniak, G.: Comparative Study of the Continuos Phase Flow in a Cyclone Seperator Using Different Turbulence Models. International Journal for Numerical Methods in Fluids, 48, 1175-1197 (2005)
Abstract: Numerical calculations were carried out at the apex cone and various axial positions of a gas cyclone separator for industrial applications. Two different NS-solvers (a commercial one (CFX 4.4 ANSYS GmbH, Munich, Germany, CFX Solver Documentation, 1998), and a research code (Post-doctoral Thesis, Technical University of Chemnitz, Germany, September, 2002)) based on a pressure correction algorithm of the SIMPLE method have been applied to predict the flow behaviour. The flow was assumed as unsteady, incompressible and isothermal. A k-ε turbulence model has been applied first using the commercial code to investigate the gas flow. Due to the nature of cyclone flows, which exhibit highly curved streamlines and anisotropic turbulence, advanced turbulence models such as Reynolds stress model (RSM) and large eddy simulation (LES) have been used as well. The RSM simulation was performed using the commercial package activating the Launder et al.’s (J. Fluid. Mech. 1975; 68(3):537-566) approach, while for the LES calculations the research code has been applied utilizing the Smagorinsky model. It was found that the k-ε model cannot predict flow phenomena inside the cyclone properly due to the strong curvature of the streamlines. The RSM results are comparable with LES results in the area of the apex cone plane. However, the application of the LES reveals qualitative agreement with the experimental data, but requires higher computer capacity and longer running times than RSM.
This paper is organized into five sections. The first section consists of an introduction and a summary of previous work. Section 2 deals with turbulence modelling including the governing equations and the three turbulence models used. ln Section 3, computational parameters are discussed such as computational grids, boundary conditions and the solution algorithm with respect to the use of MISTRAL/PartFlow-3D. In Section 4, prediction profiles of the gas flow at axial and apex cone positions are presented and discussed. Section 5 summarizes and concludes the paper.
This paper is organized into five sections. The first section consists of an introduction and a summary of previous work. Section 2 deals with turbulence modelling including the governing equations and the three turbulence models used. ln Section 3, computational parameters are discussed such as computational grids, boundary conditions and the solution algorithm with respect to the use of MISTRAL/PartFlow-3D. In Section 4, prediction profiles of the gas flow at axial and apex cone positions are presented and discussed. Section 5 summarizes and concludes the paper.
Heiland, H., G., Wozniak, K., Wozniak, G.: Ein Particle-Image-Velocimetry/Thermography System (PIV/T) zur Untersuchung thermischer Konvektionsströmungen. GALA, 13. Fachtagung „Lasermethoden in der Strömungsmesstechnik“, BTU Cottbus, 6.-8. September, 17.1 – 17.8, ISBN 3-98056132-1 (2005)
Abstract: Flüssigkristalline Substanzen können für unterschiedliche berührungslose Messzwecke eingesetzt werden, da die optischen Signale, die von den Flüssigkristallen reflektiert werden, sich in Abhängigkeit von verschiedenen physikalischen Parametern reproduzierbar andern. Diese Parameter können z. B. die Temperatur, der Druck oder auch das elektrische oder magnetische Feld sein. Eine Änderung dieser Größen wird durch eine selektive Farbreflexion von einfallendem weißem Licht der Flüssigkristalle sichtbar. Die resultierende Farbverteilung erlaubt eine quantitative Auswertung der anfallenden Messdaten. In dieser Studie wird ein Particle-lmage—Velocimetry / Thermography System (PIV/T) zur simultanen Messung der Geschwindigkeits- und Temperaturverteilung der thermischen Konvektion in einem schmalen Behälter angewendet. Die Bestimmung dieser Größen mittels elektronischer Bilddatenerfassung und -verarbeitung wird im Detail beschrieben.
Shalaby, H., Pachler, K. Wozniak, K., Wozniak, G.: Numerical Simulation of Turbulent Flow Through a Straight Square Channel. Proceedings of Applied Mathematics and Mechanics PAMM, 4, Dresden, 484-485 (2004)
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Hädrich, Th., Erdmann, H.-J.: Laser-Doppler-Messungen am Apexkegel eines Staubzyklons. GALA – 11. Fachtagung über Lasermethoden in der Strömungsmesstechnik, 11 – 13 September 2003
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A. Maurer, G. Wozniak, A. C. Hübler, W. Beier: Über das Zerstäuben von Offset-Druckfarbe. Forschung im Ingenieurwesen – Engineering Science, 1-7, 2005, ISSN: 0015-7899 (Paper) 1434-0860 (Online)
Abstract: Results from experiments on the atomization of printing ink for the application to a novel offset printing concept are presented and discussed. Offset printing ink is a highly viscous fluid exhibiting a complex rheology and thus difficult to disintegrate into fine droplets. Hence, a special atomization technique has been developed to coat the respective roller of the printing unit with ink. The article contains information on the theology of printing ink, a description of the atomization experiments and their results in form of droplet size distributions in dependence of various parameters, and a dimensional analysis of the process.
Wozniak, G.: Zerstäubungstechnik, Springer Verlag, ISBN 3-540-41170-4 (2002)
Subramanian, R. S., Balasubramanian, R., Wozniak, G.: Fluid mechanics of bubbles and drops. In: Physics of Fluids in Microgravity (Edited by R. Monti). Earth Space Institute Book Series, Taylor & Francis, London and New York (2001)
Abstract: The literature on the motion of bubbles and drops, due to the action of interfacial tension gradients which arise from temperature variation along the interface. is reviewed, highlighting recent work. First. theoretical developments are considered. These include asymptotic analyses of the motion of an isolated drop or bubble when convective transport effects are either very small or very large as well as a variety of numerical solutions of the problem. Also, theoretical work on drops interacting with other drops or with neighboring surfaces is mentioned very briefly. This is followed by a discussion of results from ground-based and reduced gravity experiments. Experiments on thermocapillary migration on the ground have been restricted to conditions wherein convective transport effects play only a small role. The only ground-based experiments in which such effects are large involve drops that are held stationary under the combined influence of gravity and thermocapillarity. Experiments were initiated under reduced gravity conditions in the late seventies, and gathered momentum in the last two decades of the twentieth century due to the availability of long periods of reduced gravity conditions aboard the United States space shuttle. We conclude this review with comments about future prospects for this field, pointing out the importance of conducting experiments under low gravity conditions.
Wozniak, G., Balasubramanian, R., Hadland, P., Subramanian, R. S.: Temperature fields in a liquid due to the thermocapillary motion of bubbles and drops. Experiments in Fluids (2001)
Abstract: Experiments were performed on the motion of isolated air bubbles and drops of Fluorinert FC-75 moving in a Dow-Corning silicone oil under the action of an applied temperature gradient in a reduced gravity environment aboard the Space Shuttle in orbit. The disturbance of the imposed temperature field due to the motion of the objects was studied optically using a shearing interferometer with a Wollaston prism and the results of a typical bubble run were compared with theoretical predictions. Also, the liquid velocity field surrounding the bubbles and drops has been qualitatively investigated in a few runs by the observation of tracer particles dispersed in the continuous phase fluid. The measurement techniques are described, and the results for the temperature and flow fields are presented and discussed.
Glathe, A., Wozniak, G., Richter, T.: The influence of eccentricity on the performance of a coaxial prefilming air-assist atomizer. Atomization and Sprays, 11, pp. 21-33 (2001)
Abstract: The influence of eccentricity of the central tube delivering the liquid to be atomized on the performance of a coaxial prefilming air-assist atomizer has been studied experimentally. Local droplet size mesurements performed using a phase Doppler anemometer show the dependense of the droplet diameter on the relative eccentricity of the liquid tube. This article presents the experimental technique and a dimensional analysis of the data. A comparison of experimental data with the developed empirical equations shows good agreement. The coefficients of the empirical equation lead to a quantification of the deviation of the Sauter mean diameter that is dependent on the leading parameters even in the spatial direction.
Koukan, E., Wozniak, G., Wozniak, K., Siekmann, J.: Experimental study of flow fields around small gas bubbles under the combined action of buoyancy and thermocapillarity. Heat and Mass Transfer 37, 437-441 (2001)
Abstract: Due to the combined action of buoyancy and thermocapillarity, the flow around a moving or stationary bubble, surrounded by a liquid matrix, exhibits a relative complex structure. The results of recent experiments show two different cases. First the buoyancy force is stronger than the thermocapillary force, secondly, the reverse relationship holds.
