07 Fakultät Konstruktions-, Produktions- und Fahrzeugtechnik

Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/8

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Open Access
On the dynamic behavior of the catalytic fixed-bed reactor in the region of multiple steady states. Pt. 1, The influence of heat conduction in two phase models
(1972) Eigenberger, Gerhart
Die Benutzung des Zweiphasenmodells für den katalytischen Festbettreaktor führte im Bereich mehrfacher stationärer Zustände bisher stets zu Schwierigkeiten, da sich ein Kontinuum von mehrfachen stationären Lösungen ergab. Dabei war es gleichgültig, ob die von Liu und Amundson aufgestellten kontinuierlichen Zweiphasenmodelle oder die von Amundson und Mitarbeitern entwickelten Zellenmodelle zugrunde gelegt wurden. In der vorliegenden Arbeit wird gezeigt, daß sich die unendliche Mannigfaltigkeit stationärer Lösungen auf wenige Lösungen reduziert, wenn man annimmt, daß Wärmeleitung in der Katalysatorphase stattfindet. Unterschiede zwischen den bisher benutzten Modellen und dem vorgeschlagenen Modell werden am Beispiel der Zündung und des Verlöschens der Reaktion dargelegt.
Open Access
On the dynamic behavior of the catalytic fixed-bed reactor in the region of multiple steady states. Pt. 2, The influence of the boundary conditions in the catalyst phase
(1972) Eigenberger, Gerhart
It has been shown in a preceding paper that a reasonable two-phase model for the catalytic fixed-bed reactor in the region of multiple steady states should take into account heat conduction in the catalyst phase. In this paper the study of the proposed model will be continued using the example of the adiabatic fixed-bed reactor. It turns out that the behavior in the region of multiple steady states is essentially affected by the boundary conditions of the catalyst phase. If one assumes that the catalyst phase is isolated adiabatically at the front of the reactor, threefold stable steady states in a wide range of hysteresis can be obtained. If heat exchange by radiation takes place in the frontal surface of the catalyst phase threefold stable steady states can also occur but the range of hysteresis is much narrower. Twofold stable steady states exist only if the fixed-bed is composed of three parts; the first and third parts consist of inert material and the second contains the active catalyst. The results of the computation of this example will be compared qualitatively with the experiments of Padberg and Wicke.
Open Access
Influence of the wall on the dynamic behavior of homogeneous tubular reactors with a highly exothermic reaction
(1974) Eigenberger, Gerhart
The influence of the tube wall on the behavior of tubular reactors with a highly exothermic reaction was studied. The effect of heat accumulation in the wall has a considerable influence upon the transient behavior of the reactor. Because of this influence excess temperatures can occur if the feed temperature is lowered or the flow velocity is raised. For a gas phase reaction the transient behavior is determined almost completely by the heat capacity of the wall. An example of multiple steady states caused by axial heat conduction in the wall is given, and the influence of heat conduction in the wall is compared with that in the reaction mixture.
Open Access
Mechanismen und Auswirkungen kinetischer Instabilitäten bei heterogen-katalytischen Reaktionen
(1976) Eigenberger, Gerhart
Die gewonnenen Ergebnisse lassen den Schluß zu, daß kinetische Instabilitäten bei heterogen-katalytischen Reaktionen mit formalkinetischen Ansätzen vom Langmuir-Typ sinnvoll beschrieben werden können. Die gelegentlich geäußerte Hoffnung, daß aus einer solchen modellmäßigen Beschreibung der Reaktion im Instabilitätsbereich Schlüsse auf die tatsächlich wirksamen Mechanismen (Mikrokinetik) der Reaktion gezogen werden können, wird allerdings selten erfüllt sein. Wie bei der Aufstellung von Langmuir-Hinshelwood-Ansätzen für eine Oberflächenreaktion ergibt sich auch hier eine beinahe unbeschränkte Mannigfaltigkeit bei der Postulation möglicher Mechanismen. Hier wie dort wird es das Ziel der reaktionstechnischen Betrachtung sein, einen möglichst einfachen Mechanismus mit einem möglichst großen Gültigkeitsbereich zu finden. Für den Fall der CO-Oxydation an Platin sollte diese Arbeit einige Hinweise dazu liefern.
Open Access
A modified Crank-Nicolson technique with non-equidistant space steps
(1976) Eigenberger, Gerhart; Butt, John B.
A finite difference method with non-equidistant space steps, based upon the Crank-Nicolson technique is presented. Its prime feature is the automatic positioning of axial grid points at required positions. Thus reducing considerably the total number of grid points and hence the amount of computer time. The method is demonstrated for a number of examples of tubular reactor calculations. It proves to be well suited for the solution of all kinds of diffusion type models, especially if steep gradients or moving profiles occur, and can be used even on moderate size process computers.
Open Access
Kinetic instabilities in catalytic reactions : a modelling approach
(1976) Eigenberger, Gerhart
It is the purpose of this contribution to show under which conditions relatively simple Langmuir-type rate mechanisms exhibit steady state multiplicity as well as periodic instabilities and may serve as models for experimentally observed phenomena.
Open Access
Kinetic instabilities in heterogeneously catalyzed reactions. Pt. 1, Rate multiplicity with Langmuir-type kinetics
(1978) Eigenberger, Gerhart
This paper is concerned with the occurrence of rate multiplicities (ignition-extinction phenomena). It is shown that rate multiplicity can be caused by the competing chemisorption of A and B upon the same active sites of the catalyst. Rate multiplicity can occur if at least one of the chemisorption or reaction steps is of second order. No rate multiplicity can be expected, if either A or B reacts via an Eley-Rideal type mechanism.
Open Access
Kinetic instabilities in heterogeneously catalyzed reactions. Pt. 2, Oscillatory instabilities with Langmuir type reactions
(1978) Eigenberger, Gerhart
An analysis of the kinetic model studied in Part I of this contribution gave no indication for the occurrance of periodic solutions. However if an additional slow chemisorption ("buffer") step is added to the model, relaxation oscillations can develop in regions where the original model exhibited multiple solutions. The behaviour of the extended model is analysed via the singular perturbation approach and by simulation. It is shown that a broad variety of slow chemisorption steps can serve as buffer with the restriction that the buffer step should not, or at least only slightly, contribute to the surface reaction.
Open Access
Real-time displacement and tilt analysis by a speckle technique using Bi12SiO20-crystals
(1980) Tiziani, Hans J.; Leonhardt, Klaus; Klenk, Jürgen
Storage of speckle pattern in real time by means of Bi12SiO20-crystals will be reported. Applying the double exposure technique, deformations, displacements as well as tilts can be analysed. The novel speckle technique displays the Young-interference fringes in quasi real time.
Open Access
Holography and speckle techniques for real time displacement deformation and vibration analysis
(1980) Tiziani, Hans J.; Klenk, Jürgen; Leonhardt, Klaus
Holographic interferometry and speckle application are powerful techniques for deformation, displacement and vibration analysis especially when they can be applied in real time. Bismuth Silicon Oxide crystals Bi12SiO20 (BSO) were used for real-time deformation, displacement and vibration analysis using holography and "speckle photography". After a short introduction of holographic interferometry for deformation measurement using BSO crystals, speckle applications for deformation, displacement and vibration analysis in real time will be discussed.
Open Access
Real-time contour holography using BSO crystals
(1981) Küchel, Michael; Tiziani, Hans J.
Contour holography can be a powerful tool for contactless measurements. Its application in real time is even more useful for the engineer. The BSO crystal was found to be appropriate for real-time contour holography using two wavelengths.
Open Access
Vibration analysis by speckle techniques in real time
(1981) Tiziani, Hans J.; Klenk, Jürgen
Vibration analysis in quasi-real time is studied by recording the time-averaged speckle pattern in a bismuth silicon oxide crystal (Bi12SiO20). When the crystal is illuminated with a spherical wave, the spatially structured information from the time-averaged speckle pattern leads to fringes in the Fraunhofer plane. No storage device is required when the appropriate wavelength is chosen for writing and reading out the information. Experimental results will be presented together with a comparison of measurements obtained with a Doppler shift vibrometer.
Open Access
Real time metrology with BSO crystals
(1982) Tiziani, Hans J.
Electro-optical crystals are used for real-time holography, optical data storage, optical information processing and more recently for speckle applications. Many ferro-electric materials were investigated, the Bi12 SiO20 (BSO), a cubic, para-electric and electro-optic material was found to be very useful for real-time holographic interferometry and speckle applications. For the application of the BSO in real-time metrology, the crystals is usually biased with a transverse electric field in the 110 or 100 crystallographic direction. Illuminating the crystal with spatially structured information in the 110 direction as a result of a hologram or speckle pattern, a space charge field is built up, leading to a refractive index variation in the crystal. Double-exposure techniques and time average exposure will be presented for real-time deformation displacement and vibration analysis and for contour line holography using a two-wavelengths method. Young's fringes of double-exposed, or in the time-average recorded speckle patterns will be attractive for real-time deformation displacement and vibration analysis.
Open Access
Lage- und Kraftregelung strukturvariabler mechanischer Systeme
(1982) Schiehlen, Werner
Strukturvariable mechanische Systeme sind in der Fertigungstechnik und bei Transportvorgängen häufig zu finden. Eine wichtige Aufgabe besteht darin, geeignete Regelgesetze für einen sanften Bewegungsablauf ohne Kraftsprünge und Kraftimpulse (Stöße) zu finden. Es werden zunächst die Bewegungs- und Reaktionsgleichungen von Mehrkörpersystemen mit Minimalkoordinaten aufgestellt. Dann werden geeignete Regelgesetze entworfen, welche die Sollbewegung sicherstellen und kleine Störungen in den Sensorsignalen ausregeln. Die Methode wird am Beispiel einer ebenen, aus sieben starren Körpern aufgebauten Gehmaschine verdeutlicht. Der Bodenkontakt des abhebenden Fußes erweist sich als vollständig steuerbar, so daß Kraftsprünge beim Übergang von der Stützphase in die Schwingphase vermieden werden können. Der auftretende Fuß erreicht den Boden ohne Stoß.
Open Access
Removing ambiguities in surface roughness measurement
(1982) Leonhardt, Klaus; Tiziani, Hans J.
A new method is presented for the measurement of surface roughness in the range Ra ≈ 0·05-10 μm. The data from a strongly defocused low-contrast image of a rough surface is scanned, and the contrast value, C = σI/<I>, is processed. A relatively low degree of spatial and temporal coherence, combined with a relatively high-image aperture and a detector aperture (which is much wider than the nominal speckle width of the corresponding highly coherent speckle pattern) led to important instrumental advantages, e.g., illumination by an incandescent lamp, simple photodetectors, short measuring times and simple, inexpensive, compact construction. The superposition of uniform intensity to the phase contrast structure, which leads to a strictly monotonic dependence of the measured contrast over a very wide range of the roughness values Ra is of great importance. Practical measurements of metallic surface standards are reported and discussed, and the theoretical aspects of the superposition of uniform intensity are pointed out with the help of a new analytic expression for the stochastic contrast.
Open Access
Real-time measurements in optical metrology
(1982) Tiziani, Hans J.
Methods as well as recording materials for real-time measurements were discussed. Electrooptical crystals can be used for nearly realtime contactless measuring techniques. The BSO was found appropriate for real-time holographic interferometry, contour line display and for deformation, displacement and vibration analysis. Furthermore, for real-time speckle photography the BSO was found to be very useful. For noise and vibration analysis of oscillating objects such as rotating car tyres, gearing boxes, turbines blades, a vibrometer based on Doppler shift measuring principles was found to be useful, leading to an amplitude and frequency analysis. For the analyse of rotating objects an image derotator is frequently used for compensation of the rotation. In optical metrology real-time methods will be useful for the engineer in future.
Open Access
Berührungslose optische Echtzeitmesstechnik
(1983) Tiziani, Hans J.
Es wird über einige Messverfahren der berührungslosen optischen Messtechnik berichtet. Neben dem Einsatz von synthetischen Hologrammen zum Formenvergleich von asphärischen Flächen werden Messverfahren zur Verformungs- und Schwingungsmessung vorgestellt. Der Einsatz fotorefraktiver Kristalle steht noch am Anfang. Verschiedene Anwendungen mit dem BSO-Kristallspeicher werden kurz diskutiert, wie holografische Interferometrie, Konturlinien-Holografie, Speckle-Anwendungen und optische Korrelation. Am Ende wird auch gezeigt, wie eine Dopplershift-Technik zur Geschwindigkeits- und Schwingungsmessung eingesetzt werden kann. Die Ergebnisse werden verglichen mit denen der Doppelpulsholografie.
Open Access
Holographic interferometry and speckle metrology : a review of the present state
(1983) Tiziani, Hans J.
The review paper will describe the present state of holographic and speckle techniques as applied to industrial measurement. The basic principles of both techniques will be outlined with special attention given to their advantages and limitations. Current developments in the field will then be described including the testlng of rotating automobile tyres by holographic interferometry and a heterodyne technique to gain an insight into noise generation mechanism. Methods for real-time holographic and speckle recording to facilitate the use of the techniques in an industrial situation will be discussed.
Open Access
Beitrag zur Verwendung von Zernike-Polynomen bei der automatischen Interferenzstreifenauswertung
(1983) Küchel, Michael; Schmieder, Thomas; Tiziani, Hans J.
Bei der automatischen Messung und anschließenden analytischen Darstellung von Phasenfrontdifferenzen in Zweistrahlinterferometern erhebt sich das Problem der Verteilung der Meßpunkte über das Interferogramm. Die Anzahl und Anordnung der StützsteIlen beeinflußt stark die Varianz der Koeffizienten einer Zernike-Entwicklung der Phasenfront. Da zur Messung von Phasenfronten mit großen Gradienten δψ/δχ und δχ/δγ die Stützstellen sehr eng gelegt werden müssen, wird eine Kombination aus lokaler und globaler ausgleichender Interpolation vorgeschlagen, bei der die Entwicklungskoeffizienten mit hoher Genauigkeit bei kurzen Rechenzeiten ermittelt werden können.
Open Access
Neue Entwicklungen der berührungslosen optischen Meßverfahren
(1983) Tiziani, Hans J.
Der berührungslosen optischen Meßtechnik haben sich neue Möglichkeiten eröffnet durch die Einführung des Lasers. Dadurch wurde die praktische Realisierung der Holographie erst möglich. Anwendung finden neue Verfahren in der berührungslosen Abstands-, Entfernungs-, Geschwindigkeitsmessung sowie Deformations-und Schwingungsmessung.