Inst. Prozess- und Verfahrenstechnik

152 Items

Recent Submissions
Composition dependent transport diffusion in non-ideal mixtures from spatially resolved nuclear magnetic resonance spectroscopy

Pantoja, Christian F. ; Muñoz-Muñoz, Y. Mauricio ; Guastar, Lorraine ; Vrabec, Jadran ; Wist, Julien (2018-10-16)

Nuclear magnetic resonance (NMR) spectroscopy is a well-established technique for the measurement of intra-diffusion coefficients. Recently, such information has been used as a basis of predictive models to extrapolate to the Fick diffusion coefficient of liquid mixtures. The present work presents a new approach to directly access the Fick diffusion coefficient by spatially resolved NMR experim...

Diffusion Coefficients of a Highly Nonideal Ternary Liquid Mixture: Cyclohexane–Toluene–Methanol

Janzen, Tatjana ; Vrabec, Jadran (2018-10-26)

To better understand diffusion phenomena in highly nonideal ternary liquid mixtures, cyclohexane–toluene–methanol is studied by equilibrium molecular dynamics (EMD) simulation. Intradiffusion and Maxwell–Stefan (MS) diffusion coefficients, being strictly kinetic properties, are predicted by EMD over the entire composition range at ambient conditions. The thermodynamic contribution to the Fick d...

Kirkwood-Buff integration: A promising route to entropic properties?

Fingerhut, Robin ; Vrabec, Jadran (2018-12-13)

Kirkwood-Buff integration (KBI) is implemented into the massively-parallel molecular simulation tool ms2 and assessed by molecular dynamics simulations of binary liquid mixtures. The formalism of Krüger et al. (P. Krüger et al., J. Phys. Chem. Lett. 4: 235–238, 2013) that adopts NVT ensemble data to the μVT ensemble is employed throughout. Taking advantage of its linear scaling with inverse sys...

Diffusion limited evaporation of a binary liquid film

Chatwell, René Spencer ; Heinen, Matthias ; Vrabec, Jadran (2018-12-21)

An analytical solution of a model fluid’s time behavior, known as the Stefan problem, is presented. A scenario is investigated in which a planar two-component liquid film is continuously evaporating into a thermodynamically non-ideal vapor phase. Evaporation is initiated and maintained by a spatial chemical potential gradient, while its rate is limited by the components’ diffusion fluxes across...

Do ternary liquid mixtures exhibit negative main Fick diffusion coefficients?

Kozlova, S. ; Mialdun, Aliaksandr ; Ryzhkov, I. ; Janzen, Tatjana ; Vrabec, Jadran ; Shevtsova, Valentina (2019-01-07)

Experimental data on Fick diffusion coefficients of ternary and higher mixtures depend on the reference frame; those which are in common use are associated with the average velocity either with respect to volume, mass or mole number. In this study, the dependence of diffusion coefficients on the reference frame is thoroughly analyzed for three ternary mixtures of different types. The first one,...

Digitalization in Thermodynamics

Forte, Esther ; Jirasek, Fabian ; Bortz, Michael ; Burger, Jakob ; Vrabec, Jadran ; Hasse, Hans (2019-01-08)

Digitalization is about data and how they are used. This has always been a key topic in applied thermodynamics. In the present work, the influence of the current wave of digitalization on thermodynamics is analyzed. Thermodynamic modeling and simulation is changing as large amounts of data of different nature and quality become easily available. The power and complexity of thermodynamic models ...

Thermodynamic Speed of Sound Data for Liquid and Supercritical Alcohols

Javed, Muhammad Ali ; Baumhögger, Elmar ; Vrabec, Jadran (2019-02-28)

Because of their caloric and thermal nature, speed of sound data are vital for the development of fundamental Helmholtz energy equations of state for fluids. The present work reports such data for methanol, 1-propanol, 2-propanol, and 1-butanol along seven isotherms in the temperature range from 220 to 500 K and a pressure of up to 125 MPa. The overall expanded uncertainty varies between 0.07% ...

Efficient implementation of advanced molecularly-based equation of state models out of the documentation level

Merchan Restrepo, Victor Alejandro (2019)

Considering the increasing number of modern thermodynamic models for engineering applications and their continuously growing algebraic complexity, in the chemical process industry and research there is a high demand for methods and mechanisms that enhance the dissemination and reuse of these models in an efficient way. Experience shows that the common practice of providing model equations as a...

Experimental and numerical analysis of non-spherical particles in fluidized process/energy technology systems

Vollmari, Kevin (2019)

Fluid flow through a packing of granular material is commonly encountered in natural processes such as deep percolation of water, in industrial processes such as the movement of petroleum/natural gas through sand/rock in oil and gas extraction as well as in fixed and fluidized beds. Fixed beds are used among others for applications such as catalytic reactions, heat transfer, filtering, adsorpti...

DEM-Simulation der Trennkurven in Siebung und Gegenstromsichtung bei geringen Gutbeladungen

Spötter, Christian ; Elskamp, Frederik ; Hennig, Manuel ; Teipel, Ulrich ; Weber, Alfred P. ; Kruggel-Emden, Harald (2017)

Zur Abtrennung von Partikeln mit unterschiedlicher Größe sind in der Feststoffverfahrenstechnik trockene Klassierprozesse zur Herstellung von engen Fraktionen von großer Bedeutung. Um das Trennverhalten von Strömungs- und Siebklassierprozessen genauer vorhersagen zu können, wurden experimentelle Resultate mit DEM-Simulationen verglichen. Bei der Siebklassierung wurde der Einfluss der Partikelfo...

Extension of process models to predict batch screening results under the influence of moisture based on DEM simulations

Elskamp, Frederik ; Kruggel-Emden, Harald (2018)

Screening is a technical simple but still not fully understood process step, which can be used in a wide field of applications to separate bulk materials according to their particle sizes. A severe issue in screening technologies is that particles frequently prevail in moist conditions, due to effects related to the environment, the material or the process. This is often not preventable, althou...

DEM simulations of screening processes under the influence of moisture

Elskamp, Frederik ; Kruggel-Emden, Harald (2018)

In a wide field of applications, screening is required to separate bulk materials according to their particle sizes. Due to environmental, material or process related effects, particles frequently prevail in moist conditions, which is not preferred due to attractive forces altering the screening efficiency, but often not preventable. As for the design of dry screening processes detailed particl...

A strategy to determine DEM parameters for spherical and non-spherical particles

Elskamp, Frederik ; Kruggel-Emden, Harald ; Hennig, Manuel ; Teipel, Ulrich (2017)

In Discrete element method (DEM) simulations the choice of appropriate contact parameters is significant to obtain reasonable results. Particularly, for the determination of DEM parameters for non-spherical particles a general straightforward procedure is not available. Therefore, in a first step of the investigation here, methods to obtain the friction and restitution coefficients experimental...

Dispersion and phase separation in liquid multiphase systems

Hohl, Lena Katharina (2019)

Microemulsion systems consisting of water, 1-dodecene and different non-ionic surfactants can develop up to three liquid phases as a function of composition and process conditions. These innovative solvent systems are promising reaction media for processes such as the hydroformylation of long-chained olefins. In this work, the influence of the third phase on the drop size distributions and the ...

Entwicklung von Fehlererkennungs-, Zustandsschätzungs-, Regelungs- und ganzzahligen Optimalsteuerungsmethoden für pulsierende, detonative Brennkammern anhand eines akustischen Ersatzsystems

Wolff, Sascha Dominik (2019)

Aktuelle Forschungsbestrebungen zur Effizienzsteigerung von Gasturbinen verfolgen häufig den Ansatz eines Wechsels des zugrundeliegenden Kreisprozesses weg vom Brayton- hin zum Humphrey-Kreisprozess. Eine vielversprechende Möglichkeit, diesen Kreisprozess technischzu realisieren, ist durch den Einsatz einer pulsierenden, druckerhöhenden Detonationsbrennkammer gegeben. Eine solche Brennkammer be...

A framework for the derivation of dynamic process models for sieving

Elskamp, Frederik (2018)

For a wide field of applications in mechanical process engineering and materials preparation technology, screening as technical simple but still not satisfactorily understood process step is well suited to separate bulk materials according to their particle sizes. Frequently, particles prevail in broad size distributions, highly non-spherical shape and under moist conditions, complicating the h...

Time Response of Shape Memory Alloy Actuators

Potapov, Pavel L. ; Da Silva, Edson P. (2000)

Force/displacement actuators with the high output power and time response can be fabricated from shape memory wires or ribbons. Typically Ni-Ti shape memory alloys are used as an active material in such actuators. They are driven by Joule heating and air convection cooling. In the present work, the time response of various types of Ni-Ti actuators having different transformation temperatures an...

Inflating a Rubber Balloon

Müller, Ingo ; Struchtrup, Henning (2002)

A spherical balloon has a non-monotonic pressure-radius characteristic. This fact leads to interesting stability properties when two balloons of different radii are interconnected, see [1, 2, 3]. Here, however, we investigate what happens when a single balloon is inflated, say, by mouth. We simulate that process and show how the maximum of the pressure-radius characteristic is overcome by the p...

Extensions of adaptive slope-seeking for active flow control

Henning, L. ; Becker, R. ; Feuerbach, G. ; Muminovic, R. ; King, Rudibert ; Brunn, A. ; Nitsche, W. (2008)

To speed up gradient estimation in a slope-seeking controller two different modifications are proposed in this study. In a first approach, the gradient estimation is based on a locally identified black-box model. A further improvement is obtained by applying an extended Kalman filter to estimate the local gradient of an input—output map. Moreover, a simple method is outlined to adapt the search...

Piezo-Polymer-Composite Unimorph Actuators for Active Cancellation of Flow Instabilities Across Airfoils

Haller, Daniel ; Pätzold, A. ; Losse, N. ; Neiss, S. ; Peltzer, Inken ; Nitsche, W. ; King, Rudibert ; Woias, P. (2011)

This article presents a smart device for active cancellation of flow instabilities. An array of two piezo unimorph actuators fabricated in piezo-polymer-composite technology is combined with a thin silicone membrane to mimic a movable wall with a closed surface. By locally displacing the thin membrane, a surface wave is generated that interferes with naturally occurring flow instabilities withi...