Showing papers on "Slug flow published in 2015"
TL;DR: In this article, both numerical and experimental studies on the hydrodynamics and heat transfer of two-phase flow without phase change in small channels and tubes are reviewed and a perspective on future directions in the field is suggested, including control through wettability and the use of novel liquids.
98 citations
TL;DR: The development of a continuously operated tubular crystallizer for the production of protein crystals has been described, and using the model enzyme lysozyme, product particles ranging between 15 and 40 μm in size are generated.
Abstract: Protein crystals have many important applications in many fields, including pharmaceutics. Being more stable than other formulations, and having a high degree of purity and bioavailability, they are especially promising in the area of drug delivery. In this contribution, the development of a continuously operated tubular crystallizer for the production of protein crystals has been described. Using the model enzyme lysozyme, we successfully generated product particles ranging between 15 and 40 μm in size. At the reactor inlet, a protein solution was mixed with a crystallization agent solution to create high supersaturations required for nucleation. Along the tube, supersaturation was controlled using water baths that divided the crystallizer into a nucleation zone and a growth zone. Low flow rates minimized the effect of shear forces that may impede crystal growth. Simultaneously, a slug flow was implemented to ensure crystal transport through the reactor and to reduce the residence time distribution.
89 citations
TL;DR: In this article, an indirect ultrasonication-assisted nucleation process is designed to vary the seed generation rate during operation independent of mass flow rate, by varying the ultrasonization power.
Abstract: Continuous-flow solution crystallization is an approach to manufacture pharmaceutical crystals with improved control of product characteristics, simplified postcrystallization operations, higher production rate flexibility, and reduced capital costs and footprint. An indirect ultrasonication-assisted nucleation process is designed to vary the seed generation rate during operation independent of mass flow rate, by varying the ultrasonication power. The ultrasonication probe is pressed against a tube to generate a spatially localized zone within the tube inside of a temperature bath for the generation of crystal nuclei without heating or contaminating the supersaturated solution. This nucleation design is integrated into a continuous slug-flow crystallization process to generate uniform-sized product crystals within each slug at a high supersaturation level and a short residence time of ∼8.5 min, without inducing significant secondary nucleation. By increasing size uniformity, the indirect ultrasonication-a...
87 citations
TL;DR: In this paper, the mass transfer coefficients of gas-liquid slug flow under elevated pressure up to 3.0 MPa in a microchannel were investigated with CO 2 -water system, and the results showed that the ratio of the initial bubble length to the unit cell length is linear with the injection gas volume fraction under each pressure condition, but the slope decreases with an increase in the system pressure.
80 citations
TL;DR: This work presents a robust, high-power and highly efficient USMR by directly coupling a microreactor plate with a Langevin-type transducer to intensify gas-liquid mass transfer of slug flow in a microfluidic channel.
Abstract: The combination of ultrasound and microreactor is an emerging and promising area, but the report of designing high-power ultrasonic microreactor (USMR) is still limited. This work presents a robust, high-power and highly efficient USMR by directly coupling a microreactor plate with a Langevin-type transducer. The USMR is designed as a longitudinal half wavelength resonator, for which the antinode plane of the highest sound intensity is located at the microreactor. According to one dimension design theory, numerical simulation and impedance analysis, a USMR with a maximum power of 100 W and a resonance frequency of 20 kHz was built. The strong and uniform sound field in the USMR was then applied to intensify gas-liquid mass transfer of slug flow in a microfluidic channel. Non-inertial cavitation with multiple surface wave oscillation was excited on the slug bubbles, enhancing the overall mass transfer coefficient by 3.3-5.7 times.
76 citations
TL;DR: In this article, the authors compared two well-known designs, namely the Y-jet and outside in gas (OIG) effervescent atomizers, with their new design (CFT) and an “outside in liquid” (OIL) configuration for the EIG atomizer.
65 citations
TL;DR: In this paper, a high-speed camera was used to investigate the flow patterns of Newtonian/non-Newtonian fluids two-phase flow in T-shaped rectangular microchannels.
Abstract: This paper presents an experimental investigation on the flow patterns of Newtonian/non-Newtonian fluids two-phase flow in T-shaped rectangular microchannels by using a high-speed camera. Three different dimensions of microchannels are employed with 400 μm × 400 μm, 400 μm × 600 μm, 400 μm × 800 μm in depth and width, respectively. The cyclohexane is used as the dispersed phase, and various concentrations of carboxyl methyl cellulose (CMC) aqueous solutions as the continuous phase. Results show that slug flow, droplet flow, parallel flow and jet flow are the main flow patterns for cyclohexane-CMC two-phase flow in rectangular microchannels. The larger the concentration of CMC solutions and the smaller the size of the microchannels are, the wider of the regimes are for the droplet flow and parallel flow. A model is proposed to predict the transitions between adjacent flow regimes for liquid–liquid two-phase flow in non-Newtonian fluids in rectangular microchannels.
59 citations
TL;DR: In this paper, the internal structure of different sub-regimes of slug flow is analyzed and five distinct slug flow subregimes are identified based on the visual observations, which correspond to slug at formation stage (onset of slug); less aerated slug; highly aerated slugs; slug and plug; and slug and wavy.
52 citations
TL;DR: The average net leakage flow in a bubble formation cycle at T-junction can be as large as 62.4% of the feeding liquid flow rate, depending on the liquid properties.
Abstract: The leakage flow is that liquid does not push gas bubbles and leaks through the channel corners. This leakage flow was confirmed by tracking particles moving in the liquid film with a double light path method and was quantified by tracking the gas–liquid interface movement. The results show that leakage flow varies during bubble formation process. The average net leakage flow Qnet-leak in a bubble formation cycle at T-junction can be as large as 62.4% of the feeding liquid flow rate, depending on the liquid properties. Qnet-leak for regular flow at main channel is much smaller, ranging from about 0 to 30% of the feeding liquid flow rate. The difference between the two leakage flows would lead to an increase in liquid slug length after generation. Finally, the effects of parameters such as phase flow rates, surface tension, and viscosity were investigated. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3964–3972, 2015
47 citations
TL;DR: In this paper, the effect of pipe inclination angle on transition boundaries between flow patterns is investigated comprehensively, showing that non-stratified flows such as bubbly and slug flows are dominant flow patterns in the upward flows and stratified flows in the downward flows.
46 citations
TL;DR: In this article, a flow visualization study is performed in an air-water test facility constructed from 3.81 cm inner diameter clear acrylic round pipes to characterize bubble interaction mechanisms and flow regime transition processes in horizontal gas-liquid two-phase flow.
TL;DR: In this article, the authors used a 2mm ID quartz glass capillary with molten tin and nitrogen and a superficial velocity of 0.092m−s−1, demonstrating that the use of molten metal in the capillary reactor is both controllable and feasible.
TL;DR: In this paper, the effect of bubble size and flow capillary number on different flow parameters, such as the shape and velocity of bubbles, thickness of the liquid film formed between the bubbles and the channel wall, and the development lengths in front and at the back of the bubbles are investigated.
Abstract: Experimental and numerical studies are performed to characterise the dynamics of isolated confined air bubbles in laminar fully developed liquid flows within channels of diameters d = 0.5 mm and d = 1 mm. Water and glycerol are used as the continuous liquid phase, and therefore, a large range of flow capillary numbers 10−4 < Ca < 10−1 and Reynolds numbers 10−3 < Re < 103 are covered. An extensive investigation is performed on the effect of bubble size and flow capillary number on different flow parameters, such as the shape and velocity of bubbles, thickness of the liquid film formed between the bubbles and the channel wall, and the development lengths in front and at the back of the bubbles. The micro-particle shadow velocimetry technique (μPSV) is employed in the experimental measurements allowing simultaneous quantification of important flow parameters using a single sequence of high-speed greyscale images recorded at each test condition. Bubble volume and flow rate of the continuous liquid phase are precisely determined in the post-processing stage using the μPSV images. These parameters are then used as initial and boundary conditions to set up CFD simulations reproducing the corresponding two-phase flow. Simulations based on the volume of fluid technique with the aim of capturing the interface dynamics are performed with both ANSYS Fluent v. 14.5, here augmented by implementing self-defined functions to improve the accuracy of the surface tension force estimation, and ESI OpenFOAM v. 2.1.1. The present approach not only results in valuable findings on the underlying physics involved in the problem of interest but also allows us to directly compare and validate results that are currently obtained by the experimental and computational methods. It is believed that similar methodology can be employed to rigorously investigate more complex two-phase flow regimes in micro-geometries.
TL;DR: In this paper, a new empirical closure relationship is proposed as a function of viscosity (viscous) and Froude (inertia) dimensionless numbers to predict the gas fraction in slugs for high-viscosity liquid (180-587mPa) and gas flow in horizontal pipes.
TL;DR: In this article, the effect of flow pattern on the performance of AVMD process and the heat and mass transfer mechanism in this process were studied, and the results showed that performance of VMD was improved obviously by air-bubbling method.
TL;DR: In this article, a multi-phase flow strategy based on oscillatory motion of a bi-phasic slug within a fluorinated ethylene propylene (FEP) tubular reactor, under inert atmosphere, is designed and developed to address mixing and mass transfer limitations associated with continuous slug flow chemistry platforms for studies of biphasic catalytic reactions.
TL;DR: In this paper, the authors investigate mass transfer characteristics during flow of immiscible liquids through glass capillaries of internal diameter 2mm and 6mm, and propose that an efficient co-current tubular contactor should be trumpet shaped with short horizontal sections connecting long vertical up and downflow sections.
TL;DR: In this article, the characteristics of air-water two-phase flow in the vertical helical rectangular channel are performed using the high speed flow visualization and the flow pattern map and the transition in the helical rectilinear channel are presented.
TL;DR: In this paper, a numerical treatment is proposed to minimize the creation of unphysical, spurious currents in modeling liquid-gas slug flow using the volume of fluid-continuum surface force (VOF-CSF) method.
Abstract: A numerical treatment is proposed to minimize the creation of unphysical, spurious currents in modeling liquid–gas slug flow using the volume of fluid-continuum surface force (VOF-CSF) method. An elongated gas slug drawn into a small circular channel initially filled with liquid is considered. To suppress spurious currents formed by numerical errors in calculation of the surface tension force at small capillary numbers (Ca < 0.01), an artificial relative reference frame is specified with motion in a direction opposite to the flow. An increase in the local relative velocity magnitude near the interface is demonstrated to be the key mechanism for spurious current suppression. A comparison of simulations performed with and without this treatment shows that spurious currents are eliminated at Ca = 0.0029; liquid film thickness, gas slug velocity, and liquid-phase circulation near the leading slug interface are preserved and the computed values agree with the literature. This demonstrates that the proposed mov...
TL;DR: The dynamic experimental results indicate that the multivariate sample entropy (MSampEn) is sensitive to complexity change of flow patterns including bubbly flow, stratified flow, plug flow and slug flow.
Abstract: Flow behavior characterization is important to understand gas-liquid two-phase flow mechanics and further establish its description model. An Electrical Resistance Tomography (ERT) provides information regarding flow conditions at different directions where the sensing electrodes implemented. We extracted the multivariate sample entropy (MSampEn) by treating ERT data as a multivariate time series. The dynamic experimental results indicate that the MSampEn is sensitive to complexity change of flow patterns including bubbly flow, stratified flow, plug flow and slug flow. MSampEn can characterize the flow behavior at different direction of two-phase flow, and reveal the transition between flow patterns when flow velocity changes. The proposed method is effective to analyze two-phase flow pattern transition by incorporating information of different scales and different spatial directions.
TL;DR: In this article, the authors quantitatively measured and described the uniformity of slug flow in multiple microchannels, defined as homogeneity of emerging bubbles, in two parallel micro-channels.
TL;DR: In this article, an ensemble-averaged digital image processing technique was applied for detection of the liquid-gas interface with aid of a set of photo gates to synchronize bubble passage with image acquisition.
TL;DR: In this paper, an infrared thermography technique, high-speed visualization, and a film thickness sensor were used to characterize vapor Taylor bubbles rising in a vertical, co-current, liquid flow.
TL;DR: In this paper, the authors examined the influence of slug length and carrier phase variations on the local Nusselt numbers in a two phase liquid-liquid Taylor flow regime and proposed a novel correlation to model the flow in the thermally developing and fully-developed regions.
TL;DR: In this paper, Gerris et al. studied slug flow in circular capillaries using the open source computational fluid dynamics (CFD) code, Gerris (Popinet, 2003, 2009), and derived new correlations for the film thickness, bubble velocity, and pressure drop.
TL;DR: In this paper, the authors investigate experimentally the flow characteristics of air/shear-thinning liquid systems in horizontal and slightly inclined smooth pipes using a high-speed camera.
Journal Article•
TL;DR: A multi-phase flow strategy, based on oscillatory motion of a bi-phasic slug within a fluorinated ethylene propylene (FEP) tubular reactor, under inert atmosphere, is designed and developed to address mixing and mass transfer limitations associated with continuous slug flow chemistry platforms for studies of bi- focusesic catalytic reactions.
Abstract: A multi-phase flow strategy, based on oscillatory motion of a bi-phasic slug within a fluorinated ethylene propylene (FEP) tubular reactor, under inert atmosphere, is designed and developed to address mixing and mass transfer limitations associated with continuous slug flow chemistry platforms for studies of bi-phasic catalytic reactions. The technique is exemplified with C–C and C–N Pd catalyzed coupling reactions.
TL;DR: In this article, an in-depth study of the slug flow pattern has been performed using image analysis, and the influence of inlet phase velocities on slug characteristics namely length, frequency and velocity of toluene plugs, in-situ tofluene fraction and relative slip between the phases has been investigated.
TL;DR: In this paper, a mechanistic model is developed for predicting the characteristics of slug flows of highly viscous liquid in horizontal pipes, where a control volume is drawn around the slug body and slug film in a slug unit.
Abstract: Slug flow characteristics in highly viscous liquid and gas flow are studied experimentally in a horizontal pipe with 0.074 m ID and 17 m length. Results of flow regime map, liquid holdup and pressure gradient are discussed and liquid viscosity effects are investigated. Applicable correlations which are developed to predict liquid holdup in slug body for low viscosity flow are assessed with high viscosity liquids. Furthermore, a mechanistic model is developed for predicting the characteristics of slug flows of highly viscous liquid in horizontal pipes. A control volume is drawn around the slug body and slug film in a slug unit. Momentum equations with a momentum source term representing the significant momentum exchange between film zone and slug body are applied. Liquid viscosity effects are considered in closure relations. The mechanistic model is validated by comparing available pressure gradient and mean slug liquid holdup data produced in the present study and those obtained from literature, showing satisfactory capabilities over a large range of liquid viscosity.
TL;DR: In this article, the two-phase flow patterns of R410A were observed in two 7.9mm inner diameter horizontal tubes filled with 5 or 10 PPI (pores per inch) copper foams.