Praktische Anwendungen der Lorentzkraft-Anemometrie. - In: Workshop Elektroprozesstechnik, (2013), 6, insges. 7 S.
The effect of a uniform magnetic field on vortex breakdown in a cylinder with rotating upper lid. - In: Computers & fluids, ISSN 1879-0747, Bd. 88 (2013), S. 510-523
The effects of an axial uniform magnetic field on vortex breakdown in the swirling flow, which is steady, axisymmetric and generated by the rotation of upper lid of an enclosed cylinder, are investigated. A collocation spectral solver is developed. After validating by dynamic and magnetohydrodynamic (MHD) problems, it is applied for the solution of the swirling flow in an enclosed cylinder with aspect ratio (height/radius) of 1:5 6 c 6 2. In the presence of an axial uniform magnetic field, the effects of magnetic field on the dimensionless lengths of vortex along the z-axis and the central positions of vortex on the zaxis are analyzed. The conductivities of the upper lid, lower base and side wall are considered. The results show that, for different electrical boundary conditions, the behaviors of vortex are significantly different and even converse. In particular, when the upper rotating lid is the only perfectly conducting, the magnetic effects are the strongest.
https://doi.org/10.1016/j.compfluid.2013.10.006
Untersuchung des realen Betriebsverhaltens von neun SolarAktivHäusern. - In: Aktiv-Solarhaus, ISBN 978-3-943891-13-3, (2013), S. 88-95
Multiscale structures in solutal Marangoni convection: three-dimensional simulations and supporting experiments. - In: Physics of fluids, ISSN 1089-7666, Bd. 25 (2013), 9, 092109, insges. 31 S.
Transient solutal Marangoni convection in a closed two-layer system is studied by a combination of numerical simulations and supplementary validation experiments. The initially quiescent, equally sized liquid layers are the phases of a cyclohexanol/water mixture. Butanol is additionally dissolved in the upper organic layer. Its diffusion across the interface is sensitive to the Marangoni instability. Complex convective patterns emerge that develop a hierarchical cellular structure in the course of the mass transfer. Our highly resolved simulations based on a pseudospectral method are the first to successfully reproduce the multiscale flow observed in the experiments. We solve the three-dimensional Navier-Stokes-Boussinesq equations with an undeformable interface, which is modeled using the linear Henry relation for the partition of the weakly surface-active butanol. Length scales in the concentration and velocity fields associated with the small and large-scale cells agree well with our experimental data from shadowgraph images. Moreover, the simulations provide detailed information on the local properties of the flow by which the evolution of the patterns and their vertical structure are analyzed. Apart from relatively weak influences due to buoyancy, the evolution of the convective structures is self-similar between different initial butanol concentrations when length and time are appropriately rescaled.
https://doi.org/10.1063/1.4821536
Experimental investigation of the velocity and temperature fields near the walls in turbulent Rayleigh-Bénard convection, 2013. - Online-Ressource (PDF-Datei: X, II, 106 S., 13,17 MB) : Ilmenau, Techn. Univ., Diss., 2013
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Für den Wärmetransport in turbulenter Rayleigh-Bénard-Konvektion sind die beiden Grenzschichten an Heiz- und Kühlplatte von besonderer Bedeutung. In der vorliegenden Arbeit wird über die Messung von dreidimensionalen Geschwindigkeits- und Temperaturfeldern in turbulenter Rayleigh-Bénard-Konvektion mittels Laser-Doppler-Anemometrie und Mikro-Thermistor berichtet. Es wurden hochaufgelöste Geschwindigkeits- und Temperaturmessungen innerhalb und außerhalb der Grenzschichten bei verschiedenen Rayleigh-Zahlen, Aspektverhältnissen und Messpositionen durchgeführt. Ein Teil der Daten wurde mit äquivalenten Ergebnissen aus direkten numerischen Simulationen (DNS) verglichen. Für die physikalische Beschreibung der Grenzschicht und für die Überprüfung von verschiedenen Grenzschichtmodellen, wie zum Beispiel die Prandtl-Blasius-Lösung, werden zeitgemittelte Geschwindigkeits- und Temperaturprofile, die Profile von deren Fluktuationen, die Skalierungsgrößen der Grenzschicht, die Scher-Reynolds-Zahl und die Invarianten des Reynoldsschen Spannungstensors bei Rayleigh-Zahlen im Bereich zwischen Ra = 3,44 × 10^9 und Ra = 9,78 × 10^{11} und für Aspektverhältnisse im Bereich zwischen [Gamma] = 1,0 und [Gamma] = 3,0 analysiert. Die dreidimensionalen Geschwindigkeitsmessungen haben gezeigt, dass in der Nähe der Kühlplatte bei Ra = 3,44 × 10^9 und Ra = 2,88 × 10^{10} keine wand-normale Geschwindigkeitskomponente existiert. Sowohl die viskose als auch die thermische Grenzschichtdicke skalieren mit der Rayleigh-Zahl wie [Delta] _v Ra^{ 0,24} und [Delta] _ [Theta] Ra^{ 0,24}. Der Vergleich der experimentell gewonnenen Daten mit denen aus der DNS basiert auf Ergebnissen bei Rayleigh-Zahlen Ra = 3 × 10^9 und Ra = 3 × 10^{10}, sowie einem festen Aspektverhältnis von [Gamma] = 1. Es zeigte sich, dass die gemessenen Geschwindigkeitsdaten sehr gut mit den DNS-Daten übereinstimmen [1], die Temperaturdaten jedoch leicht differieren. Speziell die gemessenen Temperaturprofile zeigen nicht den linearen Verlauf der DNS-Daten und die gemessenen Temperaturgradienten an der Wand sind signifikant größer als die DNS-Werte. Weiterhin wird in der Arbeit über simultane Geschwindigkeits- und Temperaturmessungen in der großen Konvektionszelle bei Ra = 8,96 × 10^{11}, [Gamma] = 1,13 an drei verschiedenen Messpositionen berichtet. Es wurden die Profile der wand-normalen Geschwindigkeit und der Temperatur untersucht sowie diffusiver und konvektiver Wärmetransport aus den gemessenen Geschwindigkeits- und Temperaturfluktuationen berechnet. Dabei zeigte es sich, dass bei der Wärmeübertragung innerhalb der Grenzschicht der diffusive und außerhalb der Grenzschicht der konvektive Transport dominiert.
http://www.db-thueringen.de/servlets/DocumentServlet?id=22807
Thermodynamic efficiency of pumped heat electricity storage. - In: Physical review letters, ISSN 1079-7114, Bd. 111 (2013), 11, 110602, insges. 5 S.
Pumped heat electricity storage (PHES) has been recently suggested as a potential solution to the large-scale energy storage problem. PHES requires neither underground caverns as compressed air energy storage (CAES) nor kilometer-sized water reservoirs like pumped hydrostorage and can therefore be constructed anywhere in the world. However, since no large PHES system exists yet, and theoretical predictions are scarce, the efficiency of such systems is unknown. Here we formulate a simple thermodynamic model that predicts the efficiency of PHES as a function of the temperature of the thermal energy storage at maximum output power. The resulting equation is free of adjustable parameters and nearly as simple as the well-known Carnot formula. Our theory predicts that for storage temperatures above 400 C PHES has a higher efficiency than existing CAES and that PHES can even compete with the efficiencies predicted for advanced-adiabatic CAES.
https://doi.org/10.1103/PhysRevLett.111.110602
Electromagnetic force on a magnetic dipole inside an annular pipe flow. - In: Physics of fluids, ISSN 1089-7666, Bd. 25 (2013), 9, 097102, insges. 9 S.
We present an illuminating example of electromagnetic flow measurement in liquid metals that is easy to analyze yet displays a remarkably good agreement with laboratory experiments. Our system involves a small permanent magnet located inside an annular pipe carrying the flow of a liquid metal. We investigate the Lorentz force acting upon the magnet using a combination of laboratory experiments with liquid metal at room temperature and a simple analytical model.We demonstrate that the measured Lorentz forces are in very good agreement with the predictions of our model over a wide range of geometry parameters. By virtue of its simplicity and close relationship to the well known creeping magnet classroom experiment, our system can also serve as an educational tool for introductory courses in liquidmetal magnetohydrodynamics.
https://doi.org/10.1063/1.4820239
Theoretical and experimental investigations of the pulse tube engine. - In: Journal of thermophysics and heat transfer, ISSN 1533-6808, Bd. 27 (2013), 3, S. 534-541
The pulse tube engine is a simple prime mover based on the pulse tube process. It has high potential to be applicable in waste heat usage. In the present work a simulation model is used to design a pressurized experimental pulse tube engine employing helium as working fluid. The measured engine characteristics are compared with the calculated predictions. Using the model and the experimental test rig, the engine performance is studied for different heat input temperatures, filling pressures, and operating frequencies. The energy conversion process, based on a broken thermodynamic symmetry and a thermal lag occurring in the pulse tube, is proven theoretically. Fundamental characteristics and application limitations of the pulse tube engine are disclosed experimentally. The obtained engine behavior provides suggestions for its further development.
http://dx.doi.org/10.2514/1.T4021
The pulse tube engine: a numerical and experimental approach on its design, performance, and operating conditions. - In: Energy, ISSN 1873-6785, Bd. 55 (2013), S. 703-715
The pulse tube engine is a simple heat engine based on the pulse tube process. Due to its simplicity it has a high potential to be applicable in waste heat usage and energy harvesting purposes. In this work, mathematical and experimental design tools are developed to study a pressurized laboratory scale pulse tube engine. The mathematical model is based on the transient numerical solution of the governing differential equations for mass, momentum and energy. The Modelica environment of SimulationX is used to solve the equations numerically and the model is employed to design the experimental test engine with helium as working fluid. The transient behavior of the pulse tube engine's underlying thermodynamic properties is studied numerically and experimentally under different design parameters as well as for different heat input temperatures, filling pressures and operating frequencies. The measured engine characteristics are compared with the calculated predictions. Internal and external power losses are quantified. Design studies for a further development of the pulse tube engine are performed experimentally. The developed numerical tool provides a rational framework for up-scaling the current laboratory model to industrial scale.
http://dx.doi.org/10.1016/j.energy.2013.03.052
Verwertungsstrategien für Lorentzkraft-Anemometer in der Materialherstellung : Schlussbericht zum BMBF ForMaT-Projekt ; Projektlaufzeit: 01.01.2010 - 30.06.2012. - Ilmenau : Univ.. - Online-Ressource (29 S., 1,01 MB)Förderkennzeichen BMBF 03FO2292
https://edocs.tib.eu/files/e01fb13/755748174.pdf