To improve the performance of particle image velocimetry in measuring instantaneous velocity fields, direct cross-correlation of image fields can be used in place of auto-correlation methods of interrogation of double- or multiple-exposure recordings. With improved speed of photographic recording and increased resolution of video array detectors, cross-correlation methods of interrogation of successive single-exposure frames can be used to measure the separation of pairs of particle images between successive frames. By knowing the extent of image shifting used in a multiple-exposure and by a priori knowledge of the mean flow-field, the cross-correlation of different sized interrogation spots with known separation can be optimized in terms of spatial resolution, detection rate, accuracy and reliability.

Theory of cross-correlation analysis of PIV images : Image analysis as measuring technique in flows

Direct numerical simulation of interphase heat and mass transfer in multicomponent vapour–liquid flows

3D modeling of hydrodynamics and physical mass transfer characteristics of liquid film flows in structured packing elements

Fundamentals and applications of CFD technology on analyzing falling film heat and mass exchangers: A comprehensive review

Dynamic and microscopic simulation of the counter-current flow in a liquid desiccant dehumidifier

Structured packed columns are widely used in the chemical industry for distillation and absorption. However, the understanding of the transfer mechanism behind the counter-current gas-liquid flow in structured packed columns is still limited. In this work, a three-dimensional CFD model that considers the local absorption and the local momentum transfer mechanism is developed for a film flow on a small plate with a counter-current gas flow. The model, based on the Volume of Fluid (VOF) method, is built up on the basis of a pressure drop model and the penetration theory to quantitatively investigate the instantaneous hydrodynamics and mass transfer characteristics of the liquid phase. Simulations and experiments are carried out for a system consisting of propane and toluene. A comparison of the simulation results with the experimental data for the outlet concentrations shows good agreement.

Computational Approach to Characterize the Mass Transfer between the Counter‐Current Gas‐Liquid Flow

The design of packed columns requires the detailed description of the hydrodynamics on the surface of the packings. To analyze the local flow behavior of the liquid phase, a three-dimensional Computational Fluid Dynamics (CFD) model was developed that applies to the two-phase countercurrent flow on an inclined and flat plate. This model, based on the volume-of-fluid (VOF) method, considers the gravity, the surface tension and the drag force between the two phases. The development of such a model allows investigation of the influences of the liquid and gas flow rates on the flow behavior such as the film flow and the rivulet flow. A validation of the model was performed using data from the literature and from experiments conducted in this work. Simulation and experimental results demonstrate that the specific wetted area on the plate decreases with decreasing liquid load. Moreover, CFD simulations reveal that the presence of the countercurrent gas phase tends to increase the fluctuation and the thickness of the film flow, which is in accordance with experimental data. It also affects the flow behavior of the rivulet flow and changes the velocity profiles for both film and rivulet flow behavior. On the other hand, the simulation results indicate that CFD is a potent tool for analyzing and investigating the flow phenomena in chemical engineering.

Portraying the Countercurrent Flow on Packings by Three-Dimensional Computational Fluid Dynamics Simulations

Packed towers are widely used for distillation processes due to their higher separation efficiency and capacity in comparison to tray towers. The separation performance of the tower depends strongly on the liquid flow behaviour inside the packing, which becomes more complex with the appearance of a second liquid phase. This type of flow behaviour can be observed in the three-phase distillation process in packed and tray towers, whereas in packed towers two immiscible liquid phases flow down the packing co-currently and vapour phase flows in counter-current flow. For a better understanding of this process it is necessary to investigate the three-phase flow behaviour inside packed towers in detail. Therefore, a simplified setup of two immiscible liquids running down an inclined steel plate is applied for the first studies. Numerical investigations are carried out with CFD and are validated with own flow measurements of the liquid spreading, surface velocity and fluid thickness on the inclined plate. Additionally, the application of the validated CFD model to the more complex geometry of a packing segment is shown in this contribution.

On the track to understanding three phases in one tower

This paper focuses on the detailed investigations of the (multi-) liquid flow behaviors on an inclined stainless steel plate in simulations and experiments. Simulations are carried out with FLUENT 6.3; a three-dimensional computational fluid dynamics model considering the gravity, surface tension, and local drag force is developed and presented. Experimental data is obtained with optical methods. One main aspect of the paper’s presentation is the validation of the developed model for the case of one-liquid phase with a countercurrent gas phase, where the parameters (e.g., the thickness and the velocity profile of the liquid phase) are compared with the simulation results and the experimental data. The other key part of the presentation is the numerical investigations with the developed model for the case of two immiscible liquid phases with a countercurrent gas phase. Results show that with the current gas flow rate, the complex flow behavior strongly depends on the (multi-) liquid flow rates and the feed...

Detailed Investigations of the Countercurrent Multiphase (Gas–Liquid and Gas–Liquid–Liquid) Flow Behavior by Three-Dimensional Computational Fluid Dynamics Simulations

Der Warme- und Stoffubergang in Packungskolonnen wird erheblich durch die komplexe Fluiddynamik der flussigen Phase beeinflusst, fur deren tiefergehendes Verstandnis zwingend Informationen uber das Geschwindigkeitsfeld benotigt werden. Zu diesem Zweck wurde eine neue μPIV (Micro Particle Image Velocimetry)-Messmethode entwickelt, bei der das Geschwindigkeitsprofil durch die bewegte wellige Oberflache gemessen wird, sodass erstmalig Analysen auf nicht transparenten Packungsmaterialien ermoglicht werden.

S. Paschke

Papers

Computational Approach to Characterize the Mass Transfer between the Counter‐Current Gas‐Liquid Flow

Portraying the Countercurrent Flow on Packings by Three-Dimensional Computational Fluid Dynamics Simulations

On the track to understanding three phases in one tower

Detailed Investigations of the Countercurrent Multiphase (Gas–Liquid and Gas–Liquid–Liquid) Flow Behavior by Three-Dimensional Computational Fluid Dynamics Simulations

Untersuchungen von Filmströmungen mittels eines neuartigen Micro Particle Image Velocimetry Messverfahrens