Relation between oil-water interfacial flow structure and their separation in the oil-water mixture flow in a curved channel: An experimental study

Piao, Linfeng,Park, Hyungmin Elsevier 2019 International journal of multiphase flow Vol.120 No.-

<P><B>Abstract</B></P> <P>We investigate the oil-water separation in a curved channel under a range of inflow conditions, focusing on the fundamental multiphase flow physics occurring at the oil-water interface. With a silicone oil (viscosity: 10 mm<SUP>2</SUP>/s, density: 935 kg/m<SUP>3</SUP>), we perform a series of water-tunnel experiments to measure the evolution of oil-water mixture flow inside a curved channel, devised for realizing a continuous and effective oil recovery (separation). The oil-water mixture velocity at the channel inlet is 1.35–2.35 m/s (Reynolds and Froude numbers based on the inlet height and length of the channel are 0.6–2.0 × 10<SUP>4</SUP> and 0.14, respectively), and we vary the inlet oil volume fraction as 0.49–0.85. We find that the efficiency of oil separation is strongly affected by the oil-water interfacial flow structures and identify two typical flow patterns: wavy oil-water interface and dispersed-oil flow. When the inlet oil fraction is high ( > 0.74), the instability occurring at the wavy oil-water interface plays a dominant role in determining the oil recovery rate (which is as high as 80% in general). As the inlet oil fraction becomes smaller ( < 0.7), on the other hand, the oil dispersion starts to appear vigorously, which interferes with the oil separation process and the recovery rate drops below 60% at the oil fraction smaller than 0.5. Through the quantitative analysis of the optically measured oil-water interface phenomena, we suggest theoretical models to predict the oil recovery rate as a function of the interfacial fluctuation of wavy oil-water interface and the fraction of dispersed oil phase, depending on the inlet flow conditions. We also propose a strategy to maximize the oil recovery rate of large-scale oil-water separation device, which is expected to be beneficial in many applications.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Continuous and large-scale separation and recovery of oil confirmed experimentally in a curved channel geometry: oil recovery rate over 80% is achieved at higher inlet oil fraction. </LI> <LI> Flow visualization of oil-water mixture flow in a channel: oil recovery performance shows a strong dependence on two interfacial flow phenomena inside the channel: wavy oil-water interface and dispersed oil flow. </LI> <LI> Quantification of the oil-phase by image processing: we introduced two dimensionless parameters related to specific flow patterns and proposed theoretical correlations to link them to the oil recovery rate. </LI> </UL> </P>

Frit-Inlet Asymmetrical Flow Field-Flow Fractionation (FI-ARIFF): A Stopless Separation Technique for Macromlecules and Nanopariticles

문명희,Mun, Myeong Hui Korean Chemical Society 2001 Bulletin of the Korean Chemical Society Vol.22 No.4

This article gives an overview of a recently developed channel system, frit-inlet asymmetrical flow field-flow fractionation (FI-AFlFFF), which can be applied for the separation of nanoparticles, proteins, and water soluble polymers. A conventiona l asymmetrical flow FFF channel has been modified into a frit-inlet asymmetrical type by introducing a small inlet frit near the injection point and the system operation of the FI-AFlFFF channel can be made with a great convenience. Since sample components injected into the FI-AFlFFF channel are hydrodynamically relaxed, sample injection and separation processes proceed without interruption of the migration flow. Therefore in FI-AFlFFF, there is no requirement for a valve operation to switch the direction of the migration flow that is normally achieved during the focusing/relaxation process in a conventional asymmetrical channel. In this report, principles of the hydrodynamic relaxation in FI-AFlFFF channel are described with equations to predict the retention time and to calculate the complicated flow variations in the developed channel. The retention and resolving power of FI-AFlFFF system are demonstrated with standard nanospheres and protreins. An attempt to elucidate the capability of FI-AFlFFF system for the separation and size characterization of nanoparticles is made with a fumed silica particle sample. In FI-AFlFFF, field programming can be easily applied to improve separation speed and resolution for a highly retaining component (very large MW) by using flow circulation method. Programmed FI-AFlFFF separations are demonstrated with polystyrene sulfonate standards and pululans and the dynamic separation range of molecular weight is successfully expanded.

Flow Field Change before Onset of Flow Separation

Hasegawa, Hiroaki,Sugawara, Takeru Korean Society for Fluid machinery 2009 International journal of fluid machinery and syste Vol.2 No.3

Jets issuing through small holes in a wall into a freestream has proven effective in the control of flow separation. This technique is known as the vortex generator jet (VGJs) method. If a precursor signal of separation is found, the separation control system using VGJs can be operated just before the onset of separation and the flow field with no separation is always attained. In this study, we measured the flow field and the wall static pressure in a two-dimensional diffuser to find a precursor signal of flow separation. The streamwise velocity measurements were carried out in the separated shear layer and spectral analysis was applied to the velocity fluctuations at some angles with respect to the diffuser. The pattern of peaks in the spectral analysis changes as the divergence angle increases over the angle of which the whole separation occurs. This change in the spectral pattern is related to the enhancement of the growth of shear layer vortices and appears just before the onset of separation. Therefore, the growth of shear layer vortices can be regarded as a precursor signal to flow separation.

Microfluidic particle separator utilizing sheathless elasto-inertial focusing

Ahn, Sung Won,Lee, Sung Sik,Lee, Seong Jae,Kim, Ju Min Elsevier 2015 Chemical engineering science Vol.126 No.-

<P><B>Abstract</B></P> <P>Microfluidics-based particle separation has attracted much attention in a wide range of chemical, environmental, and biological applications. However, most of the existing methods require complex channel designs to generate inertial flows or external forces such as electric fields. In this work, we demonstrate a facile particle separation technology with extremely simple straight channel geometry not relying on any external force. In viscoelastic flow, larger particles are enriched downstream of a straight channel in a self-modulated manner by sheathless elasto-inertial focusing mechanism (Yang et al., Lab Chip, 2011, 11, 266-273). We evaluated the performance of a microfluidic separator based on this mechanism, and found significant effects for polymer and particle concentrations, as well as flow rate. In particular, we determined an upper limit for the polymer concentration, which was attributed to the occurrence of shear-thinning behavior, and we found optimal flow rates for the separation. In addition, we found that particle-particle interaction plays an important role in the separation process and the purity of separated particles is gradually degraded with increasing particle concentration. This work will contribute to the design of microfluidic particle separators and the fundamental understanding of particle dynamics in polymer solutions flowing through confined geometries.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We demonstrated particle separation by size under microfluidic viscoelastic flow. </LI> <LI> Performance evaluation of a separator based on sheathless elasto-inertial focusing. </LI> <LI> Polymer and particle concentrations, as well as flow rate affect the separation. </LI> <LI> Existence of upper limit for polymer concentration and optimal flow rates. </LI> </UL> </P>

유동 가스 온도 변화에 따른 삼각 분리 막대형 차압 유량계 특성 연구

김광일(Kwangil Kim),유원열(Wonyuel Yoo),이충훈(Choonghoon Lee) 한국자동차공학회 2008 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-

Differential pressure flow meters which have a shape of triangular separate bar (TSB) were tested for investigating the flow characteristics of the flow meters with varying the temperature of the gas flow. Three kinds of the triangular separate bar flow meters whose aerodynamic angles are different one another are used. The mass flow rate of the flow meters are evaluated using non-dimensional parameter which includes the gas temperature, exhaust gas pressure, the differential pressure at the flow meters and atmospheric pressure. A burner system was used for raising the gas temperature. The burner system was operated with varying the air/fuel ratio by controlling both the fuel injection rate at the fuel nozzle and air flow rate from a blower. An empirical correlation between mass flow rate at the TSB flow meter and the non-dimensional parameter was obtained. The empirical correlation shows linear relationship between the mass flow rate and the non-dimensional parameter H. Also, the mass flow characteristics at the TSB flow meter was affected by the gas temperature.

Adaptive Flow Separation Control Over an Asymmetric Airfoil

Choi, Byunghun,Hong, Youkyung,Lee, Byunghyun,Kim, Minhee,Kim, H. Jin,Kim, Chongam The Korean Society for Aeronautical Space Sciences 2018 International Journal of Aeronautical and Space Sc Vol.19 No.2

A closed-loop adaptive flow control system was experimentally demonstrated to control the flow separation over an NACA 64A210 airfoil. To control the flow separation, piezoelectrically driven synthetic jet actuators and pressure sensors were used. Before performing the closed-loop flow separation control experiment, the effectiveness of the synthetic jet actuator was investigated by open-loop experiments for an NACA 64A210 airfoil in various operating conditions to examine the effective control parameter. The pressure gradient, which was calculated from the difference of mean pressure coefficients between two sensor positions, was found to be a criterion for flow recovery in these experiments. Therefore, the pressure gradient was selected as a control parameter for separated flow. An adaptive flow control system using adaptive inverse control and extremum-seeking control was developed to control the pressure gradient for separated flow over an NACA 64A210 airfoil. The performance of the resulting flow control system was compared with a simple PID control system. Experimental results based on the proposed adaptive flow control system demonstrated the satisfactory tracking performance of the pressure gradient for the pressure recovery. As a result, the proposed adaptive flow control approach enhanced the aerodynamics performances in terms of lift and drag coefficients and lift/drag ratio in the closed-loop control system.

유동 가스 온도 변화에 따른 삼각 분리 막대형 차압 유량계 유량 특성에 관한 연구

김광일(Kwangil Kim),유원열(Wonyuel Yoo),이충훈(Choong Hoon Lee) 한국생산제조학회 2008 한국생산제조학회지 Vol.17 No.4

Differential pressure flow meters which have a shape of triangular separate bar(TSB) were tested for investigating the flow rate characteristics of the flow meters with varying the temperature of the gas flow. Three kinds of the triangular separate bar flow meters whose aerodynamic angles are different one another are used. The mass flow rate of the flow meters are evaluated using a non-dimensional parameter which includes the gas temperature, exhaust gas pressure and differential pressure at the flow meters, and atmospheric pressure. A burner system which is similar to gas turbine was used for raising the gas flow temperature. The burner system was operated with varying the air/fuel ratio by controlling both the fuel injection rate from the fuel nozzle and air flow rate from a blower. An empirical correlation between the mass flow rate at the TSB flow meter and the non-dimensional parameter was obtained. The empirical correlation showed linear relationship between the mass flow rate and the non-dimensional parameter H. Also, the mass flow rate characteristics at the TSB flow meter was affected by the gas temperature.

Delayed Detached-Eddy Simulation of Subsonic Axisymmetric Base Flow

정민재,윤예지,허서연,지솔근 한국항공우주학회 2023 International Journal of Aeronautical and Space Sc Vol.24 No.4

Axisymmetric base flow is investigated to understand flow physics associated with the massive flow separation at a subsonic speed. The detached-eddy simulation (DES) approach is well suited in the current separated flow with a known separation point. The upstream attached boundary layer is well represented with the Reynolds-averaged Navier–Stokes (RANS) mode, whereas the separated flow from the base is well captured in the large-eddy simulation (LES) mode. Since the spatial resolution in the LES zone impacts directly the fidelity of the DES computation, a systematic approach is applied to the computational grid. Current computational grids are designed for nearly isotropic grids in the separated region (i.e., LES zone) with much reduced anisotropy of the grid in the separating shear layer, compared to computational grids documented in literature. Current grids allow the separating shear layer to undergo the Kelvin–Helmholtz instability, resulting in a rapid shift from the RANS to LES mode right after the flow separation. In consequence, the axisymmetric base flow is well resolved in the current DES computation with good agreement to relevant experimental data including the mean base pressure and the center-line velocity in the wake. The base flow is further discussed with statistical data of the separated flow. Current DES simulation is also compared with a typical RANS simulation to emphasize the high fidelity of the computational approach.

A field study of colloid transport in surface and subsurface flows

Zhang, Wei,Tang, Xiang-Yu,Xian, Qing-Song,Weisbrod, Noam,Yang, Jae E.,Wang, Hong-Lan Elsevier, etc 2016 Journal of hydrology Vol.542 No.-

<P><B>Abstract</B></P> <P>Colloids have been recognized to enhance the migration of strongly-sorbing contaminants. However, few field investigations have examined combined colloid transport via surface runoff and subsurface flows. In a headwater catchment of the upper Yangtze River, a 6m (L) by 4m (W) sloping (6°) farmland plot was built by cement walls to form no-flow side boundaries. The plot was monitored in the summer of 2014 for the release and transport of natural colloids via surface runoff and subsurface flows (i.e., the interflow from the soil-mudrock interface and fracture flow from the mudrock-sandstone interface) in response to rain events. The water sources of the subsurface flows were apportioned to individual rain events using a two end-member model (i.e., mobile pre-event soil water extracted by a suction-cup sampler <I>vs</I>. rainwater (event water)) based on <I>δ</I> <SUP>18</SUP>O measurements. For rain events with high preceding soil moisture, mobile pre-event soil water was the main contributor (generally >60%) to the fracture flow. The colloid concentration in the surface runoff was 1–2 orders of magnitude higher than that in the subsurface flows. The lowest colloid concentration was found in the subsurface interflow, which was probably the result of pore-scale colloid straining mechanisms. The rainfall intensity and its temporal variation govern the dynamics of the colloid concentrations in both surface runoff and subsurface flows. The duration of the antecedent dry period affected not only the relative contributions of the rainwater and the mobile pre-event soil water to the subsurface flows but also the peak colloid concentration, particularly in the fracture flow. The <10μm fine colloid size fraction accounted for more than 80% of the total suspended particles in the surface runoff, while the colloid size distributions of both the interflow and the fracture flow shifted towards larger diameters. These results highlight the need to avoid the application of strongly-sorbing agrochemicals (e.g., pesticides, phosphorus fertilizers) immediately before rainfall following a long no-rain period because their transport in association with colloids may occur rapidly over long distances via both surface runoff and subsurface flows with rainfall.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Subsurface flow was apportioned into rainwater and mobile pre-event soil water. </LI> <LI> The duration of no-rain period affects peak colloid concentration. </LI> <LI> Rainfall intensity and its temporal variation govern colloid discharge dynamics. </LI> </UL> </P>

Estimation of Baseflow based on Master Recession Curves (MRCs) Considering Seasonality and Flow Condition

양동석,이서로,이관재,김종건,임경재,김기성 한국습지학회 2019 한국습지학회지 Vol.21 No.1

Baseflow which is one of the unmeasurable components of streamflow and slowly flows through underground is important for water resource management. Despite various separation methods from researches preceded, it is difficult to find a significant separation method for baseflow separation. This study applied the MRC method and developed the improved approach to separate baseflow from total streamflow hydrograph. Previous researchers utilized the whole streamflow data of study period at once to derive synthetic MRCs causing unreliable results. This study has been proceeded with total nine areas with gauging stations. Each three areas are selected from 3 domestic major watersheds. Tool for drawing MRC had been used to draw MRCs of each area. First, synthetic MRC for whole period and two other MRCs were drawn following two different criteria. Two criteria were set by different conditions, one is flow condition and the other is seasonality. The whole streamflow was classified according to seasonality and flow conditions, and MRCs had been drawn with a specialized program. The MRCs for flow conditions had low R2 and similar trend to recession segments. On the other hand, the seasonal MRCs were eligible for the baseflow separation that properly reflects the seasonal variability of baseflow. Comparing two methods of assuming MRC for baseflow separation, seasonal MRC was more effective for relieving overestimating tendency of synthetic MRC. Flow condition MRCs had a large distribution of the flow and this means accurate MRC could not be found. Baseflow separation using seasonal MRC is showing more reliability than the other one, however if certain technique added up to the flow condition MRC method to stabilize distribution of the streamflow, the flow conditions method could secure reliability as much as seasonal MRC method.