arXiv subjects

Somasekhara Goud Sontti

Publications and source records attributed to Somasekhara Goud Sontti.

At least 19 recordsLinked to original sources

arXiv2025

Numerical Insights on Controlled Droplet Formation in a Microfluidic Flow-Focusing Device

In this article, we have developed a computational model to determine the droplet formation regime and its transition in a square microfluidic flow-focusing device that eventually dictate the droplet shape, size, and its formation frequency. We have methodically explored the influences of various physicochemical parameters on the droplet dynamics and flow regime transition, which are essential in the development of new methods for on-demand droplet generation. On the basis of the droplet formation mechanism, we have formulated flow maps for different liquid-liquid systems, and have also proposed a scaling law to predict the droplet length for a wide range of operating condition resulting from the variation of flow rates, and viscosities of the continuous phase as well as the interfacial tension. This work can effectively contribute in providing helpful guidelines on the design and operations of droplet-based flow-focusing microfluidic systems.

physics.flu-dyn↗

arXiv2025

CFD study on Taylor bubble characteristics in Carreau-Yasuda shear thinning liquids

In the present study, Taylor bubble formation in two-phase gas-non-Newtonian Carreau liquid flowing through a confined co-flow microchannel is investigated. Systematic analysis are carried out to explore the influences of rheological properties, inlet velocities, and surface tension on Taylor bubble length, shape, velocity and liquid film thickness. Aqueous solutions of carboxymethyl cellulose (CMC) with different mass concentrations are considered as the non-Newtonian liquids to understand the fundamentals of flow behaviour. With increasing solution viscosity and liquid phase inlet velocity, Taylor bubble formation frequency and velocity increased, however, the bubble length was found to decrease. Velocity profiles inside the Taylor bubble and liquid slug were analyzed, and distinct velocity distributions were found for different CMC concentrations. Flow pattern maps are constructed based on inlet velocities for Carreau liquids in co-flow microchannel. This study essentially provides useful guidelines in designing non-Newtonian microfluidic system for precise control and manipulation of Taylor bubbles.

physics.flu-dyn↗

arXiv2025

Formation characteristics of Taylor bubbles in power-law liquids flowing through a microfluidic co-flow device

Formation and dynamics of Taylor bubble in power-law liquids flowing through a circular co-flow microchannel are numerically investigated using coupled level set and volume-of-fluid method. Aqueous solutions of polyacrylamide (PAAm) are used as power-law liquids. Influences of PAAm concentration, gas-liquid velocities, and surface tension on bubble characteristics are explored. Various mechanism of bubble breakup are observed in different concentration of PAAm. Based on the bubble length with respect to the channel diameter, two different flow regimes are identified. Flow pattern maps are constructed based on inlet velocities, and scaling laws are proposed to estimate the bubble length.

physics.flu-dyn↗

arXiv2025

Enhanced accumulation of bitumen residue in a highly concentrated tailings flow by microbubbles from in-situ catalytic decomposition of hydrogen peroxide

The massive volume of oil sands tailings has been one of the most challenging environmental issues. In this work, we experimentally explore a simple and effective approach to bitumen residue separation from a highly concentrated slurry flow of the artificial oil sands tailings. By utilizing microbubbles from in-situ catalytic decomposition of H2O2 at low concentrations, bitumen aggregation is enhanced on the top part of the hydrotransport pipeline. The microscopic image analysis revealed the in-situ formation of microbubbles and confirmed that magnetic particles present in the slurries contributed to the fast release of the gas products and bubble formation from hydrogen peroxide decomposition. A high-speed camera was applied to capture images of the tailings flow in the pipeline through a transparent view window. A large number of tiny bubbles were identified post to the injection of H2O2 to the slurry flow. More than 70 % bitumen could be recovered from a lab-scale pipeline loop within 30 mins after injection. The bitumen recovery efficiency from the collected froth was quantitatively compared under seven conditions with varied dosages, the concentration of H2O2, and the amount of magnetic solids in the slurries. Our results confirmed that the total dosage of H2O2 is the dominant factor in in-situ microbubble formation for enhanced bitumen aggregation in the flow. Importantly, microbubbles were generated rapidly in the real mature fine tailings. The results from our study provide insights into the preferential distribution of oil residue in the flow during hydrotransport without the requirement for an additional device. Removal of oily residues from concentrated slurries may bring economical and environmental advantages.

physics.flu-dyn↗

arXiv2025

Effects of Coal Particles on Microbubble-Enhanced Bitumen Separation in the Concentrated Slurry Flow of Oil Sands Tailings

Our study investigates the segregation of bitumen residues within the transport pipeline before disposal in the presence of coal particles in carriers and microbubbles. Coal particles decreased the bitumen recovery by 17% without the injection of microbubbles. In addition, the improvement in bitumen recovery efficiency by 6 mL of H2O2 is negligible due to a small number of bubbles formed from H2O2 decomposition in the flow. However, tremendous enhancement in the recovery efficiency was achieved with the simultaneous addition of coal particles and H2O2. Further increase in recovery was noted as a larger volume of H2O2 was injected to form more microbubbles. Computational fluid dynamics (CFD) simulations were conducted to help understand the effects of coal particles and microbubbles. The simulation results illustrated that the introduction of coal particles caused bitumen contents to accumulate in the middle of the pipe. Furthermore, an increased volume fraction of microbubbles contributed to a higher distribution of bitumen at the top of the pipe. This study not only offers valuable insights for developing an innovative strategy to enhance the efficiency of bitumen separation in hydrotransport processes but also contributes to a deeper understanding of the intricate interactions among bubbles, bitumen, and coal particles in a slurry flow.

physics.flu-dyn↗

arXiv2025

Understanding the Influence of Rheological Properties of Shear-Thinning Liquids on Segmented Flow in Microchannel using CLSVOF Based CFD Model

In this study, two phase gas-shear-thinning liquid flow in a square microchannel is numerically investigated using the coupled level set and volume of fluid (CLSVOF) methods. A systematic investigation is carried out to explore the influence of polyacrylamide (PAM) concentration, surface tension, velocity ratios, and contact angle on the gas slug length, volume, unit cell length, and pressure drop. Three different concentrations of PAM solutions, which exhibit shear-thinning behaviour are considered as the continuous phase. Gas slug length, volume, and unit cell length decreased with increasing the PAM concentration. Velocity and non-homogeneous viscosity distributions in the liquid slug for three different PAM concentration solutions are reported. Gas slug length decreases with an increase of the contact angle and the bubble shape change from convex to concave. This numerical work provides the fundamental insights in segmented flow formation and two-phase flow characteristics comprising shear-thinning liquids.

physics.flu-dyn↗

arXiv2025

CFD analysis of microfluidic droplet formation in non-Newtonian liquid

A three-dimensional, volume-of-fluid (VOF) based CFD model is presented to investigate droplet formation in a microfluidic T-junction. Genesis of Newtonian droplets in non-Newtonian liquid is numerically studied and characterized in three different regimes, viz., squeezing, dripping and jetting. Various influencing factors such as, continuous and dispersed phase flow rates, interfacial tension, and non-Newtonian rheological parameters are analyzed to understand droplet formation mechanism. Droplet shape is reported by defining a deformation index. Near spherical droplets are realized in dripping and jetting regimes. However, plug shaped droplets are observed in squeezing regime. It is found that rheological parameters have significant effect on the droplet length, volume, and its formation regime. The formation frequency increases with increasing effective viscosity however, the droplet volume decreases. This work effectively provides the fundamental insights into microfluidic droplet formation characteristics in non-Newtonian liquids.

physics.flu-dyn↗

arXiv2025

CFD Analysis of Taylor Bubble in a Co-Flow Microchannel with Newtonian and Non-Newtonian Liquid

We present a CFD based model to understand the Taylor bubble behavior in Newtonian and non-Newtonian liquids flowing through a confined co-flow microchannel. Systematic investigation is carried out to explore the influence of surface tension, inlet velocities, and apparent viscosity on the bubble length, shape, velocity, and film thickness around the bubble. Aqueous solutions of carboxymethyl cellulose (CMC) with different concentrations are considered as power-law liquid to address the presence of non-Newtonian continuous phase on Taylor bubble. In all cases, bubble length was found to decrease with increasing Capillary number, inlet gas-liquid velocity ratio, and CMC concentration. However, bubble velocity increased due to increasing liquid film thickness around the bubble. At higher Capillary number and inlet velocity ratio, significant changes in bubble shapes are observed. With increasing CMC concentration, bubble formation frequency and velocity increased, but length decreased.

physics.flu-dyn↗

arXiv2025

Regulation of droplet size and flow regime by geometrical confinement in a microfluidic flow-focusing device

We have developed a coupled level set and volume of fluid-based computational fluid dynamics model to analyze the droplet formation mechanism in a square flow-focusing microchannel. We demonstrate a flexible manipulation of droplet formation and flow regime based on the modified flow-focusing microchannel with a constricted orifice. Furthermore, we have systematically studied the influence of geometrical confinement, flow rate, and interfacial tension on the droplet formation regime, length, volume, velocity, and shape. Three different flow regimes, namely squeezing, dripping, and jetting, are observed, and the flow regime maps are formulated based on the Reynolds and capillary numbers. After an extensive numerical investigation, we described the boundaries between the different regimes. Droplet shape is also quantified based on the deformation index value. Plug-shaped droplets are observed in the squeezing regime, and near spherical droplets are found in the dripping and jetting regimes. Our study provides insights into the transition of a regime under various geometrical confinement and fluid properties. The results reveal that the modified flow-focusing microchannel can substantially enhance dripping while decreasing the squeezing regime, which is of paramount importance from the standpoint of producing high throughput stable and monodisperse microdroplets. Eventually, this work emphasizes the importance of geometrical confinement, fluid properties, and flow conditions on the droplet formation process in a flow-focusing microchannel that can effectively provide helpful guidelines on the design and operations of such droplet-based microfluidic systems.

physics.flu-dyn↗

arXiv2025

Numerical analysis of controlled droplet formation surrounded by shear-thinning fluid in a co-flow microfluidic device

In this work, we used a coupled level set and volume of fluid (CLSVOF) computational method for studying the generation of microdroplets in a two dimensional circular co-flow microfluidic device. The fundamental understanding of shear thinning behavior on controlled droplet formation in a microchannel is systematically investigated. Droplet generation and dynamics are controlled by altering the operating conditions and fluid properties, such as CMC solution concentration, both fluids flow rates, and interfacial tension. The droplet length, velocity, liquid film thickness, and formation frequency are quantitatively analyzed and presented in a non-dimensional form. The droplet length decreased with the flow rate and concentration of the CMC solution. However, the length of the droplet increased with dispersed phase flow rate and interfacial tension. From the set of simulation data, the flow regime maps and scaling relations are developed over a range of operating conditions. This work provides critical insights into the uniform and controlled droplet formation in shear-thinning fluids within a circular co flow microchannel, offering guidance for future innovations in the design and optimization of microfluidic systems for specific applications.

physics.flu-dyn↗

arXiv2025

High-throughput controlled droplets generation through a flow-focusing microchannel in shear-thinning fluids

This study presents a three-dimensional transient computational fluid dynamics simulation of droplet generation in a flow-focusing microfluidic device using the Coupled Level Set and Volume of Fluid method for interface capturing. We systematically investigated the effects of shear-thinning non-Newtonian fluids, specifically carboxymethyl cellulose solutions, on the generation of mineral oil droplets. The rheological properties of carboxymethyl cellulose were analyzed at concentrations of 0.1%, 0.25%, 0.5%, and 1.0%, with the parameters K and n specified in terms of viscosity. The study examines the influence of rheological properties, continuous and dispersed phase flow rates, and interfacial tension forces on the generation and dynamics of controlled high-throughput droplets. The numerical results provide insights into droplet characteristics, including droplet length, velocity, formation frequency, liquid film thickness, pressure distribution, and flow regimes. The findings revealed that increasing the carboxymethyl cellulose concentration (0.1% to 1.0%) and continuous phase flow rate (10 μL/min to 30 μL/min) reduces droplet length by 53% and 45%, respectively. while increasing the dispersed phase flow rate (2 μL/min to 18 μL/min) and interfacial tension results in increased droplet length by 62% and 42%. At lower concentrations of carboxymethyl cellulose, plug-shaped droplets fully occupy the channel width in the squeezing regime. As concentration increases, a transition to the dripping and jetting regimes is observed. The study further explores non-dimensional parameters, expressing the Weber and modified Capillary numbers as functions of flow rate and interfacial tension. These insights impact drug delivery, material synthesis, and microfluidic technologies requiring precise droplet control.

physics.flu-dyn↗

arXiv2025

Impacts of flow velocity and microbubbles on water flushing in a horizontal pipeline

Water flushing to remove particle sediment is essential for safe and continuous transport of many industrial slurries through pipelines. An efficient flushing strategy may reduce water consumption and the cost associated with water usage, and help water conservation for sustainability. In this study, a computational fluid dynamics (CFD) model coupled with the kinetic theory of granular flow for the flushing process is presented. The CFD models were validated against field data collected from a coal slurry pipeline of 128 $km$ in length, 0.575~$m$ in diameter, achieving an average error of less than 15\% for outlet solid concentration over time. A parametric study evaluated the effects of water velocity (1.88-5.88~$m/s$), bubble size (50~$μm$, 150~$μm$, and 1000~$μm$) and bubble volume fraction (0.05-0.2) on flushing performance including pipeline cleanness, cleanness efficiency, and water consumption. The obtained outcomes indicate that higher water velocity is preferred and an increase in water velocity from $1.88~m/s$ to $5.88~m/s$ reduces the water consumption by $28\%$. Large bubbles may hinder the flushing process and increase the water consumption by $23\%$. Remarkably, small bubbles facilitates the flushing process and lead to $35\%$ reduction in water consumption. These effects are attributed to the turbulent characteristics in the pipelines in presence of microbubbles.

physics.flu-dyn↗

arXiv2025

Numerical investigation on solids settling in a non-Newtonian slurry inside a horizontal flume

Slurry transportation is always crucial for many industrial processes. This study numerically investigates the settling behavior of multisize solid particles in a non-newtonian slurry inside a semicircular open channel (flume). The non-newtonian slurry is modelled using a three-dimensional (3D) unsteady Eulerian-Eulerian (E-E) model coupled with the Hershel-Bulkley (HB) rheological model. A detailed sensitivity analysis of drag models is performed to establish the solid-fluid interaction in the slurry flow. The numerical model is validated with the experimental data from the literature and shows a fair agreement. The validated model is used to simulate the settling behavior of the slurry in the flume. The mean particle diameter of the solid particles in the slurry is in the range of 75-296 $μ$m with a median diameter of 188 $μ$m. The effect of particle size distributions (PSDs), flume inclination, bubble size and bubble volume fraction on the particle settling inside the flume is investigated in the parametric study. The analysis of our results revealed that the settling of solids is significantly affected by PSDs in the open channel system. In particular, the increase in flume inclination progresses the settling and dissipation of fine and coarse particles, respectively. Additional simulations showed that the inception of bubbles influences the settling velocity of solids, which changes the settling behavior of multisize solids inside the flume. The presented study can be used as a valuable guideline for the optimisation of intermediate exclusion of water from thickened slurry in order to ensure the stability of tailing storage facility.

physics.flu-dyn↗

arXiv2024

Numerical insights from population balance model into the distribution of bitumen residues in industrial horizontal pipes during the hydrotransport of oil sands tailings

Pipeline transportation is a vital method for conveying crushed oil sand ores and tailings in the oil sands industry. This study focuses on enhancing economic benefits by exploring the separation of valuable bitumen residues from coarse sand tailings within hydrotransport pipelines. Employing three-dimensional transient Eulerian-Eulerian computational fluid dynamics (CFD) simulations coupled with a population balance model (PBM), we examine the aggregation and breakage of bitumen droplets under various flow conditions. The CFD-PBM model's accuracy is validated against field measurements of velocity profiles and pressure drops. Our findings reveal that higher slurry velocities lead to intensified particle-bitumen interactions, resulting in reduced aggregated bitumen droplet sizes at the pipeline's core. Additionally, variations in bitumen fraction cause shifts in the distribution of coarse particles along the pipe's vertical axis, with increased aggregation and larger droplets in the upper region. Notably, we demonstrate that smaller bubbles promote a more uniform distribution of bitumen compared to larger bubbles. These insights provide valuable knowledge for optimizing bitumen recovery processes, facilitating the integration of pipeline dynamics with downstream separation and extraction units.

physics.flu-dyn↗

arXiv2022

Review of microscale dynamics of dilution-induced asphaltene precipitation under controlled mixing conditions

As the most complex and heaviest component in bitumen, asphaltene precipitation induced by solvent dilution is important in oil sands extraction to remove solids and water from bitumen froth through dilution by paraffinic solvents. This review will compare asphaltene precipitation to dilution-induced solvent shifting in aqueous systems via the ouzo effect. We attempt to highlight similarities and differences in the evolution of nanodroplets and effects from solvent mixing conditions and point out mutual experimental techniques and modeling approaches for the research of both asphaltene precipitation and nanodroplet formation. The review will start from basic concepts in both asphaltene precipitation and the ouzo effect, then move on to the effects of solvent mixing on asphaltene precipitation in bulk. After that, we will introduce advances in microfluidic systems combined with cutting-edge experimental and simulation tools for asphaltene precipitation induced under controlled mixing with solvents and a droplet formation. Such comparison will inspire more in-depth understanding and control of asphaltene precipitation and the ouzo effect in aqueous systems.

physics.flu-dyn↗

arXiv2022

Ultrasensitive Surface-Enhanced Raman Spectroscopy Detection by Porous Silver Supraparticles from Self-Lubricating Drop Evaporation

This work demonstrates an original and ultrasensitive approach for surface-enhanced Raman spectroscopy (SERS) detection based on evaporation of self-lubricating drops containing silver supraparticles. The developed method detects an extremely low concentration of analyte that is enriched and concentrated on sensitive SERS sites of the compact supraparticles formed from drop evaporation. A low limit of detection of 10^-16 M is achieved for a model hydrophobic compound rhodamine 6G (R6G). The quantitative analysis of R6G concentration is obtained from 10^-5 to 10^-11 M. In addition, for a model micro-pollutant in water triclosan, the detection limit of 10^-6 M is achieved by using microliter sample solutions. The intensity of SERS detection in this approach is robust to the dispersity of the nanoparticles in the drop but became stronger after a longer drying time. The ultrasensitive detection mechanism is the sequential process of concentration, extraction, and absorption of the analyte during evaporation of self-lubrication drop and hot spot generation for intensification of SERS signals. This novel approach for sample preparation in ultrasensitive SERS detection can be applied to the detection of chemical and biological signatures in areas such as environment monitoring, food safety, and biomedical diagnostics.

physics.chem-ph↗

arXiv2022

Computational fluid dynamics investigation of bitumen residues in oil sands tailings transport in an industrial horizontal pipe

Bitumen residues in the oil sand tailings can be a threat to the environment that separating them from tailings before disposal is crucial. However, low bitumen concentration in the tailings slurry and the complex transport characteristics of the four-phase mixture make the process difficult. This study establishes an Eulerian-Eulerian CFD model for an industrial-scale oil sand tailings pipeline. A comprehensive sensitivity analysis was conducted on the selection of carrier-solid and solid-bitumen drag models. The combination of small and large particle sizes (i.e., 75 & 700 um) and bitumen droplet size (i.e., 400 um) provided good agreement with field data in velocity profiles and pressure drop. The validated model was subsequently extended to investigate the influence of the secondary phase (i.e., bitumen droplets and bubbles) on flow characteristics in a tailing pipeline. The investigation covered a range of bitumen droplet size (100-400 um), bitumen fraction (0.0025-0.1), bubble size (5-1000 um), and bubble fraction (0.0025-0.3) and their influences on the velocity, solids, and bitumen distribution are revealed. For an optimum bubble size of 500 um, a maximum recovery of 59% from the top 50 % and 83 % from the top 75 % of the pipe cross-section was obtained. The present study demonstrates the preferential distribution of bitumen and provides valuable insight on bitumen recovery from an industrial-scale tailings pipeline.

physics.flu-dyn↗

arXiv2022

Asphaltene precipitation under controlled mixing conditions in a microchamber

Solvent exchange is a controlled process for dilution-induced phase separation. This work utilizes the solvent exchange method to reveal the effect of the mixing dynamics on the asphaltene precipitation process under 20 different mixing conditions using a model system of n-heptane and asphaltene in toluene. The external mixing between the asphaltene solution and the paraffinic solvent is strictly controlled. We employed a high-spatial-resolution total internal reflection fluorescence microscope to detect asphaltene precipitates with a resolution up to 200 nm. A multiphysics model is used to simulate the evolution of the oversaturation pulse in the solvent exchange process. Based on the simulation results, we predicted the effect of the flow rate, dimension, the orientation of the microfluidic chamber, and temperature on the surface coverage and size distribution of asphaltene precipitates. The model predictions of all factors corroborate with the experimental observations. Local concentration of the solvent and shear forces are found to be the two main reasons for the change of asphaltene precipitation caused by mixing dynamics. However, the influence of thermodynamics is more critical than the mixing dynamics as temperature changes. Through a combination of experimental and simulation studies, this work illuminates the significance of the transportation process for the final morphology of asphaltene precipitates and provides an in-depth insight into the mechanism of mixing dynamics on the asphaltene precipitation. A smart mixing may be to boost new phase formation without excessive solvent consumption.

physics.flu-dyn↗