Plug Velocity Research Articles

Control of plug flow dynamics in microfluidic T-junction using pulsations of dispersed phase flow rate

Active control methods are commonly employed in droplet-based microfluidics. While passive methods of droplet generation face limitations, active methods, including flow rate pulsations provide an avenue for precise control. We investigate the influence of sinusoidal pulsations of dispersed phase flow rate on the plug flow dynamics in a T-junction microchannel. The study covers a range of fluid sets, including gas-liquid and liquid-liquid systems. In the absence of pulsations, distinct regimes of plug formation were identified, and plug length, velocity, and natural frequency of formation were determined. Introducing flow rate pulsations at frequencies proportional to the natural ones f = fpulse/fplug, we observed distinct plug length distributions, including double- or triple-mode, drop-on-demand mode, and multi-mode distribution. The influence of pulsations on plug length was particularly notable at low dimensionless frequencies (f < 1), especially for fluid combinations with higher viscosity ratios. The model was proposed to explain plug length distribution patterns under pulsatile conditions. Micro-PIV measurements provided insights into the velocity fields within plugs, revealing the stretching of streamlines without altering plug length. Our findings contribute to the understanding of active control methods in droplet-based microfluidics and suggest potential applications for precise control over microfluidic processes.

Desulfurization of Zawia Refinery Diesel Using Adsorption Fixed Bed Process

The study focuses on the dynamic modeling of a fixed-bed adsorber for the adsorption of sulfur compounds in diesel fuel. The model considers non-ideal plug flow behavior and velocity variation along the column, providing a more realistic representation of the adsorption process. Additionally, internal mass-transfer resistances due to pore diffusion mechanisms are incorporated into the model. The study investigates adsorption performance by examining different flow rates (5 cc/min, 10 cc/min, 15 cc/min, and 20 cc/min) and inlet concentrations ranging from 586 to 100 ppm. The bed height is constant at 30 cm. The behavior of various parameters, such as bed utilization, breakpoint time, film mass transfer coefficient, and height of the adsorption zone, is analyzed. The results indicate that a sharp front of the breakthrough curve is observed, followed by the broadening of the tail of the breakthrough curve. The breakthrough curve represents the adsorbate concentration in the effluent stream over time. The investigation reveals that a high flow rate of 20 cc/min and a high inlet concentration yield better overall bed capacity utilization for the adsorption system. This means that the bed is more effectively utilized at higher flow rates and higher inlet concentrations, leading to improved adsorption performance. In conclusion, high flow rates and high inlet concentrations are favorable for enhancing the adsorption system's performance in terms of bed utilization. These results provide valuable insights for optimizing the design and operation of fixed-bed adsorbers that remove sulfur compounds from diesel fuel.

Experimental observation and pressure drop modeling of plug formation in horizontal millifluidic hydraulic conveying.

The hydraulic conveying of glass beads is studied in a horizontal tube. At low flow rates, plugs can be observed moving across the tube, whereas pseudoplugs can be seen at higher flow rates. A statistical analysis of the plugs' and pseudoplugs' velocities and the plugs' lengths observed is conducted. A transition of the propagation speed distribution is established when the crossing over from a plug to a pseudoplug regime is reached, where the peaked plug velocity distribution turns into a uniform pseudoplug velocity distribution. On the other hand, the statistical distribution of plug lengths exhibits a log-normal mathematical shape. The interpretation of the measured pressure drop evolution with the imposed flow rate by means of an effective viscosity shows an apparent shear-thinning effect coming from the dilution of the granular material. This approach provides a predictive tool for pressure drop calculation in the pseudoplug regime.

Biomechanics of abdominal aortic aneurysm in the framework of Windkessel effect and fully-developed inflow velocity via two-way non-linear FSI

Abdominal aortic aneurysm (AAA) is a pathological condition characterised by localised dilation of the infrarenal aorta, which can be fatal if rupture occurs. Current diagnostic criteria for repair are not patient-specific, but computational modelling may help to predict the potential growth and risk of AAA rupture accurately. This paper highlights how important using the Windkessel effect and fully-developed inflow velocity framework for the biomechanical analysis of AAA is; in other words, this research investigates how different boundary conditions in modelling methods affect the ability to correctly represent the biomechanics of AAA with complex non-linear parameters using a two-way fluid–structure interaction (FSI) technique. Time-averaged wall shear stress (TAWSS) is highly sensitive to boundary conditions, so unrealistic or simplified boundary conditions can lead to very different TAWSS results. This study also revealed that the use of outflow 3-element Windkessel boundary conditions on pulsatile pressure affects the flow pattern and increases the flow recirculation period. By accounting for the Windkessel effect and preventing backflow in numerical studies of AAA, the maximum displacement found in the distal branches can also be reduced. Models assuming plug velocity profiles overestimate peak wall stress by approximately 20% compared with models using fully developed parabolic inlet velocity profiles. This study incorporated a three-layer anisotropic material model and non-Newtonian fluid properties into the simulation, providing a more realistic representation of the effect of boundary condition selection on AAA mechanics. The results summarised from the parametric study could contribute to better prediction of AAA growth and rupture risk, and have important implications for the development of improved treatment strategies for AAA patients.

Predictive modelling approach for cottonseed plug velocity applying a circuit theory analogy

In this study, a circuit theory analogy was used to investigate plug behaviour in dense phase pneumatic conveying of cottonseeeds. It was found that the time series aeration/deaeration pressure drop of a fixed bed exhibits exponential behaviour, similar to the charging/discharging of a capacitor in a circuit. Using this analogy, the pressure drop below transition superficial air velocity was considered equivalent to the potential voltage across a capacitor over time. By extending this analogy beyond transition superficial air, a potential pressure drop was introduced and found to separate from the measured pressure drop at the moment the plug moves. It was demonstrated that the difference between the potential and measured pressure drop can be scaled to the plug velocity, indicating a linear relationship between these variables. This approach provides a novel method for understanding and predicting plug behaviour in pneumatic conveying, which may have practical applications for various types of other materials.

Experimental Study of Mass Transfer in a Plug Regime of Immiscible Liquid–Liquid Flow in a T-Shaped Microchannel

In the presented work, the influence of parameters such as the total flow rate of phases, the ratio of flow rates, and residence time on mass transfer during the two-phase flow of immiscible liquids in a T-shaped microchannel was investigated using the micro-LIF technique. The study focused on the plug flow regime, where a 70% water–glycerol solution was used as the dispersed phase, and tri-n-butyl phosphate (TBP) was used as the carrier phase. We determined the transition boundary between the dispersed and parallel flow patterns and calculated the plug length and velocities to develop a mass transfer model. Furthermore, we measured the partition coefficient for the set of liquids used in the experiments and analyzed the concentration fields inside the slugs of the continuous phase at various distances downstream of the T-junction. Using the obtained data, we determined the extraction efficiency and overall volumetric mass transfer coefficient and established dependencies demonstrating the effect of the flow-rate ratio, total flow rate, and the residence time on mass transfer rate and extraction efficiency. Finally, we developed a model for the overall volumetric mass transfer coefficient corresponding to the set of liquids used with an R-squared value of 0.966.

Numerical Investigation of Flow Patterns and Plug Hydrodynamics in a 3D T-junction Microchannel

A three-dimensional (3D) numerical simulation of a two-phase flow liquid/liquid is performed in a rectangular microchannel with a T-junction. The volume of fluid (VOF) method was used under ANSYS Fluent to capture the interface between the two phases. The dynamic mesh adaptation technique together with the assumption of symmetry plane helps us to reduce the computational cost. The study focuses on the flow patterns and hydrodynamics of plugs. So, the influence of the flow rate ratio $$q$$ , the capillary number $$Ca$$ , and the viscosity ratio on the liquid film, the plug/droplet shape, and velocity are examined here. Particularly, the plug/droplet lengths predicted by the simulation show good agreement with the experimental and correlation available in the literature. The results revealed six distinct flow patterns by dispersing water in a continuous phase of silicone oil. By decreasing the flow rate ratio as well as the viscosity ratio, the liquid film thickness increases in the corners and side planes. In turn, this greatly impacts the liquid film velocity and the plug velocity. Furthermore, capillary number (based on two-phase flow velocity) is also shown to have a greater impact than viscosity ratio and flow rate ratio on plug shape, with the curvature radii of the tail always larger than the front one.

Experimental and numerical studies of separation intensification in segmented flow microreactors

Process intensification studies have already been well-established in continuous operations, particularly achieved by using microreactors. Separation intensification benefits from the application of process intensification and shows great potential, yet it is still not sufficiently studied. In this work, liquid-liquid two-phase segmented flow capillary microreactors and simulation models based on finite element method were used to perform experimental and numerical studies on the extractive separation intensification of the Zn-Cd-Mn system, respectively. The influence of hydrodynamics including metal ion concentration, plug velocity, and initial pH of the aqueous phase on the separation factor was explored. By regulating the hydrodynamic conditions, higher separation factors are obtained in shorter times to achieve separation intensification. The Damkhler number (Da) was introduced to clarify the rate-determining step and elaborate the separation mechanism. During the simulations, the results obtained from the model based on the finite element method agree well with the experimental ones. Taking advantage of the strong complementarity between numerical and experimental studies, separation intensification can be more deeply understood.

Experimental investigation on the motion of a single plug and its constituent particles in a horizontal pneumatic pipeline

In this study, the revolution of individual plug constituent particles, the relation between plug length and pressure drop, and the relation between plug velocity and pressure drop were experimentally examined, for a single plug in a negative pressure system, using high-speed video cameras. The horizontal pipeline consists of an 8.8 m long, 30 mm i.d. transparent acrylic tube. The particles used are three kinds of uniform spherical ABS resin particles of 6.0 mm diameter and different densities, and the non-spherical polyethylene pellet of 3.27 mm spherical equivalent diameter. By observing the plug-constituent particles, it was found that more than 65% of spherical particles revolve and about 33–39% of them are forward revolving. Some plug-constituent particles revolve in reverse due to the frictional force between the particles. For non-spherical particles, more than half revolve, although the revolution axis frequently changes and most revolutions are intermittent. Furthermore, a plug begins to be conveyed spontaneously as soon as it is generated, and plug length increases up to a definite length depending on the pressure drop across the plug.

Experimental analysis and transient numerical simulation of a large diameter pulsating heat pipe in microgravity conditions

A multi-parametric transient numerical simulation of the start-up of a large diameter Pulsating Heat Pipe (PHP) specially designed for future experiments on the International Space Station (ISS) are compared to the results obtained during a parabolic flight campaign supported by the European Space Agency. Since the channel diameter is larger than the capillary limit in normal gravity, such a device behaves as a loop thermosyphon on ground and as a PHP in weightless conditions; therefore, the microgravity environment is mandatory for pulsating mode. Because of a short duration of microgravity during a parabolic flight, the data concerns only the transient start-up behavior of the device. One of the most comprehensive models in the literature, namely the in-house 1-D transient code CASCO (French acronym for Code Avancé de Simulation du Caloduc Oscillant: Advanced PHP Simulation Code in English), has been configured in terms of geometry, topology, material properties and thermal boundary conditions to model the experimental device. The comparison between numerical and experimental results is performed simultaneously on the temporal evolution of multiple parameters: tube wall temperature, pressure and, wherever possible, velocity of liquid plugs, their length and temperature distribution within them. The simulation results agree with the experiment for different input powers. Temperatures are predicted with a maximum deviation of 7%. Pressure variation trend is qualitatively captured as well as the liquid plug velocity, length and temperature distribution. The model also shows the ability of capturing the instant when the fluid pressure begins to oscillate after the heat load is supplied, which is a fundamental information for the correct design of the engineering model that will be tested on the ISS. We also reveal the existence of strong liquid temperature gradients near the ends of liquid plugs both experimentally and by simulation. Finally, a theoretical prediction of the stable functioning of a large diameter PHP in microgravity is given. Results show that the system provided with an input power of 185W should be able to reach the steady state after 1min and maintain a stable operation from then on.

Numerical study on the pipe flow characteristics of grouting repairing pastes used in slab track

In this study, the pipe flow characteristics of the grouting repairing pastes (GRPs) used in slab track were investigated based on three-dimensional flowing models taking into account the hydration effects. Firstly, the rheological properties of GRPs at different hydration times were measured and fitted to obtain key rheological parameters of GRPs. Then the flowing models of GRPs in pipes were established based on these rheological parameters and were verified by comparing with theoretical values. Finally, the effects of pressure gradients, pipe diameters and cement hydration on the flow characteristics of GRPs were systematically studied in terms of four indices including plug diameter, plug velocity, average velocity and the velocity ratio. Results show that the increases of pipe diameters and pressure gradients both lead to the growth of flow velocity, causing an inhomogeneity flow of GRPs in pipes. Yield stress of GRPs has the greatest influence on the flow indices. Consistency index contributes more to plug velocity and average velocity while fluid behavior index dominates the velocity ratio. To achieve a homogeneous flow at high flow rate, it is recommended to prepare a grouting repair material with moderate yield stress and low consistency index and fluid behavior index. Moreover, cement hydration causes noticeable decreases of plug velocity and average velocity under the coupling effects of rheological parameters, which may lead to the setting of GRPs near pipe wall and eventually to the occurrence of pipe blockage during transportation. In order to satisfy efficient repairing in short skylight period, it is suggested to adopt a special grouting repair material featured with slow hydration during grouting but rapid hardening after filling in the debonding area.

Real-time imaging and analysis of cell-hydrogel interplay within an extrusion-bioprinting capillary

Additive manufacturing platforms are transforming research and industrial sectors worldwide. In regenerative medicine and pharmaceutical applications, they facilitate the development of patient-specific devices for implantation, as well as in vitro models of tissues and organs for disease modelling and drug screening. A key example is extrusion-based bioprinting, where a bioink that contains cells, biomolecules and a support matrix (often hydrogel), is extruded through a narrow capillary onto a platform forming the desired structure. The printing parameters and hydrogel flow behavior likely determine the extent to which cells are damaged mechanically as they pass through the capillary. Here, we present direct observations of the hydrogels and suspended cells during the printing process to help elucidate conditions potentially leading to mechanical damage and cell death. Light-sheet fluorescence microscopy was applied to observe the real-time flow of bioinks through a capillary mimicking the conditions found in bioprinting. Bioink formulations exhibiting constant and shear thinning viscosities, along with UV-crosslinked gelatin methacrylol (GelMA) were studied, and cell viability of post-printed gels were measured via fluorescent imaging. Cell tracking enabled flow profiles of bioinks to be deduced. In agreement with current flow simulations, the constant and shear thinning formulations displayed a Poiseuille flow profile although with a plug velocity profile for the latter. The UV-crosslinked GelMA formulation exhibited a two-phase annular flow with gel morphologies depicting gross-melt fractures attributed to over-gelled hydrogels. Cell viability was higher in UV-crosslinked GelMA at high flow rates compared to uncrosslinked GelMA. The findings presented here will improve modeling cell-material flow during bioprinting through accurate estimation of flow conditions, in particular for complex materials. The novel imaging approach could be further exploited to provide process monitoring and feedback to improve the outcomes of 3D bioprinting.

Comparing single‐phase, non‐Newtonian approaches with experimental results: Validating flume‐scale mud and debris flow in HEC‐RAS

AbstractPost‐fire debris flows and tailing impoundment failures destroy lives and property. These geologic hazards – and other similar processes – fall on a continuum between classic Newtonian flood analyses and geotechnical stability analyses. The US Army Corps of Engineers (USACE) is developing a non‐Newtonian library (DebrisLib) that includes a suite of rheological and clastic approaches to hyper‐concentrated, mudflow and debris flow dynamics. The Hydrologic Engineering Center (HEC) has implemented these non‐Newtonian methods into the widely used, public‐domain open‐channel hydraulics and morphodynamic software, HEC‐RAS (river analysis system). This work presents part of the verification and validation of these non‐Newtonian approaches, applying several rheological equations to published laboratory results high‐concentration flume experiments.This study tested the linear Bingham model as well as the turbulent and Bagnold quadratic terms of the O'Brien equation. HEC‐RAS also includes the non‐linear Herschel–Bulkley (HB) approach, which quantifies shear‐thickening or shear‐thinning processes. The study used these non‐Newtonian models in HEC‐RAS to simulate 10 of Parsons et al.’s (2001) flume experiments, which measured the snout and plug velocity of fluids with high solid concentrations (Cv = 68–74%) and a broad range of material gradations (d50 = 0.05–1 mm, d15 = 0.006–0.1 mm). The experiments also measured and back‐calculated Bingham and HB parameters of the materials, finding HB powers between 0.45 and 1.25 (i.e. fluids that are dilatant, pseudo‐plastic and visco‐plastic).The rheological models incorporated into DebrisLib and implemented in HEC‐RAS reproduce experimental data well for most experiments. The Bingham model generated a plug velocity root‐mean‐square error (RMSE) of 0.21 m/s using standard flow parameters and Parsons et al.’s calibrated parameters, a substantial improvement over the unmodified shallow water flow equations (RMSE 0.77 m/s). Experiments with strong snout effects tended to generate higher residuals, especially in the snout velocity. The RMSE associated with the O'Brien equation was larger with the Parsons et al. fit parameters, but similar (0.23 m/s) with measured parameters. The turbulent parameter was the largest (often the dominant) parameter in most O'Brien simulations, with the dispersive stress only proving significant for the coarsest material. DebrisLib had to use a modified version of the dispersive term to simulate these concentrations. Both the 2D depth‐averaged shallow water equation (SWE) and diffusion wave equation were used to simulate the experiments. The best results were obtained with the SWE with horizontal mixing.

Viscosity Ratio Influence on Liquid‐Liquid Flow in a T‐shaped Microchannel

AbstractThe ratio of the dispersed phase viscosity to that of the continuous phase is a critical parameter for microfluidic two‐phase flows. Here, the influence of the viscosity ratio on liquid‐liquid flow in T‐shaped microchannels is studied experimentally. Three basic flow patterns, i.e., parallel, plug, and droplet flow, are observed for different sets of immiscible liquids. Flow pattern maps are plotted and generalized using a combination of Weber and Ohnesorge dimensionless numbers. In the plug flow pattern, interface deformations occur for low viscosity ratios. Existing correlations from the literature are tested against experimental data for plug velocity and lengths. Despite the significant plug interface deformations, the influence of the viscosity ratio on the plug length and velocity is negligible.

Stochastic sensitivity analysis of volcanic activity

In the present paper, we study the stochastically induced behavior of a nonlinear volcanic model containing three prognostic variables: the plug velocity u, the pressure p under the plug, and the conduit volume V. The nouvelle phenomena of noise‐induced transitions from the equilibrium to the cycle in the bistability parametric zone and noise‐induced excitement with the generation of spike oscillations in the monostability zone are found in the presence of N‐shaped friction force. To study these phenomena numerically, we used the computations of random solutions, the phase trajectories and time series, the statistics of interspike intervals, and the mean square variations. To study these phenomena analytically, we applied the stochastic sensitivity function technique and the confidence domains method. This approach is used to predict the noise‐induced transition from a “dormant volcano” state to the “active volcano” mode. From the physical point of view, the volcano is capable to become active under the influence of external noises in the friction force, which model various compositions and properties of volcanic rocks. What is more, the volcanic plug can pop out when its slipping becomes heavy, and the volcano can erupt.

Experimental investigation and constitutive modelling of the deformation behaviour of high impact polystyrene for plug-assisted thermoforming

This paper concerns the experimental and numerical study of the plug-assisted thermoforming process of high impact polystyrene (HIPS). The thermomechanical properties of this polymer were characterized at different temperatures and deformation rates. To study the influence of different parameters in the real conditions of plug-assisted thermoforming process, we carried out “plug-only” tests at different temperatures and plug velocities. To model the deformation behaviour of HIPS, we proposed a thermo-elastic-viscoplastic model, which we have implemented in Abaqus software. A thermo-dependent friction model was also proposed and implemented in Abaqus software. The parameters of the proposed models were identified by the inverse analysis method in the real conditions of plug-assisted thermoforming. The proposed models were validated with “plug-only” tests and plug-assisted thermoforming of yogurt container.

Ionic liquid-water flow in T-shaped microchannels with different aspect ratios

In this article we investigate the influence of a rectangular microchannel aspect ratio on the liquid–liquid flow. An ionic liquid was chosen as one of the working fluids due to a vast scope of applications. Immiscible ionic liquid-water flow in T-shaped microchannels with 160μm hydraulic diameter and aspect ratios equal to 2 and 4 was studied experimentally. Flow pattern maps were drawn and compared for two channels in terms of We*Oh dimensionless number. Parallel flow was shown to prevail for the channel with higher aspect ratio. The influence of channel aspect ratio on plug flow peculiarities was studied in detail. Plug length and velocity were measured at different bulk flow rates. Velocity fields in aqueous plugs were measured using the micro-PTV technique. Velocity circulations were calculated for different flow rates. Total circulation value inside plugs was found to be higher in the channel with the lower aspect ratio.

Particle velocity and stationary layer height analysis for modification and validation of particulate Plug-2 pressure drop model

For the plug flow mode of dense-phase pneumatic conveying, three different types of plugs have been defined, and models for predicting the pressure drop in conveying pipeline have been established. In literature, the model for Plug-2 pressure drop is mechanistic and depends on several properties of the materials forming the plug. Therefore, modification of the model with experimentally corrected material properties is considered in this study. The parameters tested in this study are plug velocity, particle velocity, and the stationary layer height. Using the new functional relationships, the Plug-2 pressure drop model is modified and its predictions are compared with experimentally measured pressure drops obtained in conveying Plug-2. It is found that the modified Plug-2 pressure drop model matches experimental values well within the variation range of ±20%. Further, a detailed analysis of various types of related velocities is presented and a new type of plug, called ‘Plug-2*’, is developed.

Transport of a Micro Liquid Plug in a Gas-Phase Flow in a Microchannel.

Micro liquid droplets and plugs in the gas-phase in microchannels have been utilized in microfluidics for chemical analysis and synthesis. While higher velocities of droplets and plugs are expected to enable chemical processing at higher efficiency and higher throughput, we recently reported that there is a limit of the liquid plug velocity owing to splitting caused by unstable wetting to the channel wall. This study expands our experimental work to examine the dynamics of a micro liquid plug in the gas phase in a microchannel. The motion of a single liquid plug, 0.4–58 nL in volume, with precise size control in 39- to 116-m-diameter hydrophobic microchannels was investigated. The maximum velocity of the liquid plug was 1.5 m/s, and increased to 5 m/s with splitting. The plug velocity was 20% of that calculated using the Hagen-Poiseuille equation. It was found that the liquid plug starts splitting when the inertial force exerted by the fluid overcomes the surface tension, i.e., the Weber number (ratio of the inertial force to the surface tension) is higher than 1. The results can be applied in the design of microfluidic devices for various applications that utilize liquid droplets and plugs in the gas phase.

Experimental investigation on vertical plug formation of coarse particles by a non-mechanical feeder

ABSTRACT Plug flow receives attention due to its advantages of low particle attrition, low pipeline wear and low energy consumption. A novel non-mechanical draft tube type feeder (DTF) for plug formation has been proposed in our previous study for vertical plug conveying of coarse particles. We further investigate the influence of key geometry parameter of the DTF on plug formation for different particle diameter. Furthermore, we attempt to extend the application of PIV technique to evaluate plug velocity in pneumatic plug conveying. Experiments for vertical plug formation are conducted with glass beads of three kinds of particle diameter (i.e. 6 mm, 4 mm and 2 mm). Plug formation characteristics are examined in terms of flow pattern in riser pipe, solids mass flowrate and pressure fluctuation. The experimental results show that four main features of plug flow pattern in the riser pipe are observed. Solids mass flowrate displays good linear relation to superficial gas velocity forthe same particle diameter in the plug flow regime, even with different relative entrainment height. Some interesting phenomena are observed for the pressure fluctuation. Plug velocity is successfully obtained by PIV technique with high temporal resolution. The present study provides a further understanding of the flow pattern and dynamic behavior of coarse particles in vertical plug formation with the draft tube type feeder.