Showing papers on "Slug flow published in 2011"

Extraction in microreactors: Intensification by adding an inert gas phase

Abstract: The influence of an inert gas phase on liquid extraction using a microstructured device is analyzed. The gas phase establishes a modified flow pattern. The performance of the gas–liquid–liquid flow is compared to that of a segmented two phase flow, as regards mass transport as well as separation. The extraction of vanillin dissolved in water with toluene was chosen as an example and experiments at different residence times were conducted by varying the total volumetric flow rate. μ-PIV measurements were performed to reveal the influence of the inert gas phase on recirculation within the liquid slugs. Addition of the gas leads to an increase in mass transfer at flow velocities above 0.08 m/s. However, no difference can be noted at lower flow velocities and longer residence times, respectively. The two liquid phases were separated within the microstructured device by using a capillary separator. Purity was always higher than 96%. For two phase segmented flow, the toluene phase was pure, whereas the water phase was free of toluene rests when applying the inert gas phase. Thus, the inert gas phase can be used to enhance mass transfer under certain circumstances and to tune the separation behavior of a capillary separator.

Quantitative prediction of flow patterns in liquid–liquid flow in micro-capillaries

Abstract: Flow patterns in microstructured reactors (or microchannels) play an important role in dictating the mass transfer rates. In the present work, experiments were carried out to investigate the two phase (liquids) flow patterns in microchannels with different cross sections and contacting geometries. The pattern formation was analysed and conditions were classified in the three regions: surface tension dominated (slug flow), transition (slug-drop and deformed interface flow) and inertia dominated region (annular or parallel flow). A criterion for liquid-liquid flow pattern transition was developed using Capillary and Reynolds numbers based on the work of Dessimoz et al. Ill for gas-liquid systems. Finally, it was applied to the literature data and good agreement was obtained. The criterion is suitable for capillaries with hydraulic diameter up to 3 mm independently of cross section form and is an important predictive tool for the rational design of micro reactors for liquid-liquid reactions. (C) 2011 Elsevier B.V. All rights reserved.

Liquid/Liquid Slug Flow Capillary Microreactor

Abstract: The liquid-liquid slug flow capillary microreactor offers an excellent mass transfer performance for extraction and biphasic reactions. In combination with a simple phase separator based on wettability discrimination between the two liquids, it provides a powerful tool for process intensification and microscale processing. By new visualization techniques, the interfacial surface and slug vortex structures dictating inter- and intraphase mass transfer have been revealed to be more complex than previously assumed. Suspending fine catalyst particles in one phase of a two-phase slug flow is an effective technique for using heterogeneous catalysts in microreactors, owing to the very good mass transfer characteristics and because catalyst recovery becomes simply a matter of separating the catalyst carrier phase from the reaction medium. To exploit the performance attributes of capillary microreactors at higher throughputs, distributor and control strategies for parallelisation were developed to provide a flow distribution uniform to within 1 % or less.

Micromechanic modeling and analysis of the flow regimes in horizontal pneumatic conveying

Abstract: Pneumatic conveying is an important technology for industries to transport bulk materials from one location to another. Different flow regimes have been observed in such transportation processes, but the underlying fundamentals are not clear. This article presents a three-dimensional (3-D) numerical study of horizontal pneumatic conveying by a combined approach of discrete element model for particles and computational fluid dynamics for gas. This particle scale, micromechanic approach is verified by comparing the calculated and measured results in terms of particle flow pattern and gas pressure drop. It is shown that flow regimes usually encountered in horizontal pneumatic conveying, including slug flow, stratified flow, dispersed flow and transition flow between slug flow and stratified flow, and the corresponding phase diagram can be reproduced. The forces governing the behavior of particles, such as the particle–particle, particle-fluid and particle-wall forces, are then analyzed in detail. It is shown that the roles of these forces vary with flow regimes. A general phase diagram in terms of these forces is proposed to describe the flow regimes in horizontal pneumatic conveying. © 2011 American Institute of Chemical Engineers AIChE J, 2011

Wax Deposition in the Oil/Gas Two-Phase Flow for a Horizontal Pipe

Abstract: An experimental flow loop was designed and constructed to perform the wax deposition tests under the oil/gas two-phase flow conditions in a horizontal pipe. The oil sample came from the Daqing Oilfield of China, which was characterized by high wax content. A particular local sampler was designed and installed at the outlet of the test section in the flow loop to make up for the drawback of no visual observation during the course of flow pattern verification, which is a good device to help verify the flow pattern by analyzing the inner flow situations at different circumferential and vertical positions. Using the local sampler in combination with analyzing the changes in pressure drop and liquid holdup, which is defined as the fraction of an element of pipe occupied by liquid at the same instant, flow patterns were identified and divided into two main categories, namely, the stratified flow and slug flow. Wax deposition tests were selected in the definite flow pattern regions instead of flow pattern transi...

Modeling of pressure losses for the slug flow of a gas–liquid mixture in mini- and microchannels

Abstract: In addition to the previously constructed model of the hydrodynamics of a gas-liquid slug flow, a mathematical model is developed that describes pressure losses taking into account the rearrangement of a velocity profile in liquid slugs and energy losses on the formation and renewal of interfacial area during the motion of bubbles. The contribution of different forms of pressure losses in capillaries is analyzed. It is shown that in microchannels tangential stresses on the surface of a bubble substantially affect the total pressure losses. It is found that the length of bubbles does not affect the rate of surface formation and respective pressure losses if bubbles have the same velocity. The results of modeling are in satisfactory agreement with experimental data of other researchers.

Systems and methods for acid gas removal

Abstract: A method and system for the selective removal of CO2 and/or H2S from a gaseous stream containing one or more acid gases. In particular, a system and method for separating CO2 and/or H2S from a gas mixture containing an acid gas using an absorbent solution and one or more ejector venturi nozzles in flow communication with one or more absorbent contactors. The method involves contacting a gas mixture containing at least one acid gas with the absorbent solution under conditions sufficient to cause absorption of at least a portion of said acid gas. The absorbent contactors operate in co-current flow and are arranged in a counter-current configuration to increase the driving force for mass transfer. Monoliths can be used that operate in a Taylor flow or slug flow regime. The absorbent solution is treated under conditions sufficient to cause desorption of at least a portion of the acid gas.

Statistical characterization of two-phase slug flow in a horizontal pipe

Abstract: The present paper reports the results of an ongoing project aimed at providing statistical information on slugs in two-phase flow in a horizontal pipe. To this end, the flow was examined experimentally and numerically. On the experimental side, three non-intrusive optical techniques were combined and employed to determine the velocity field and bubble shape: particle image velocimetry (PIV), Pulsed Shadow Technique (PST) and Laser-Induced Fluorescence technique (LIF). Statistical information was provided by photogate cells installed at two axial positions. The flow was numerically determined based on the one-dimensional Two-Fluid Model. The tests were conducted on a specially built transparent pipe test section, using air and water as the working fluids. The velocity fields were obtained for flow regimes where the slugs were slightly aerated to facilitate the utilization of the optical methods employed. The main parameters for characterizing the statistically steady flow regime such as slug length and velocity obtained numerically were compared with the experimental data and good agreement was obtained.