Plug Length Research Articles

Enrichment and Separation of Cationic, Neutral, and Chiral Analytes by Micelle to Cyclodextrin Stacking-Micellar Electrokinetic Chromatography.

Analyte focusing by micelle to cyclodextrin stacking (MCDS) in micellar electrokinetic chromatography (MEKC) using sodium dodecyl sulfate (SDS) and fused silica capillaries is demonstrated for neutral, cationic, and chiral analytes. The stacking was at a dynamic boundary formed between the injected charged SDS micelles and neutral γ-cyclodextrin (γ-CD) zones, where the analytes bound inside micelles were released due to the formation of stable SDS-CD inclusion complexes. The complex formation reduced or eliminated the affinity of the analytes to the micellar phase. There was reversal (for charged) or nulling (for neutrals) of the analyte's effective electrophoretic mobility that caused the analytes to accumulate at the boundary. Under the conditions where the SDS micelles velocity is faster than the electroosmotic flow (using acidic buffer), MCDS was conducted by injection of a long plug of sample in a micellar diluent after injection of a CD solution plug into a capillary that was filled with MEKC background solution. By simply extending the length of the CD plug, chiral separations of chlorpheniramine and phenoxyacid herbicides were achieved without optimizing the MEKC conditions. The analytical figures of merit including linearity and repeatability for the tested compounds were found acceptable, and the sensitivity enhancement factors were up to 171. The stacking strategy in MEKC was applied to metabolic stability studies of small molecules with HepG2 cell line, where the samples were only treated with acetonitrile and then diluted with the micellar diluent (demonstrating the reduction of tedious sample preparation requirements for biological samples prior to chemical analysis).

Flow patterns and plug/slug flow characteristic of R134a in a 0.643 mm microchannel tube

This paper presents visualization of the two-phase flow of R134a in a 24-port microchannel tube with the average hydraulic diameter of 0.643 mm. The experiment is conducted on the same facility in the previous work for R32 (Li and Hrnjak, 2019). Mass flux covers the range from 50 to 250 kg-m−2s−1. The two-phase flow is generated by adding heat in several steps to originally subcooled refrigerant at the very entrance. When mass flux is 50 kg-m−2s−1, no annular flow is observed in the tube. The annular flow starts at x = 0.9 when mass flux is 100 kg-m−2s−1 and x = 0.6 when 250 kg-m−2s−1. The transitional flow starts at x = 0.25 (G = 50 kg-m−2s−1) and x = 0.8 (250 kg-m−2s−1). Revellin and Thome (2007), Ong and Thome (2011), and Zhao and Hu (2000) correlations are plotted against the measurements. None of them fit our data since the experiment is in lower mass flux than the database of their correlations’. The interface velocity and vapor plug length fraction (close to void fraction) are measured from the high speed videos. The velocity and vapor fraction agree to results based on the homogeneous assumption. In plug/slug flow, both the vapor plug and liquid slug lengths are uneven. The length distribution of plug and slug seems to follow Beta distribution. When the quality is low, the quantity of short vapor plugs is larger than long plugs. At fixed mass flux, when quality increases, length of vapor plugs increases and length of liquid slugs decreases.

Field Performance of Open-Ended Prestressed High-Strength Concrete Pipe Piles Jacked into Clay.

The behavior of open-ended pipe piles is different from that of closed-ended pipe piles due to the soil plugging effect. In this study, a series of field tests were conducted to investigate the behavior of open-ended prestressed high-strength concrete (PHC) pipe piles installed into clay. Two open-ended PHC pipe piles were instrumented with Fiber Bragg Grating (FBG) sensors and jacked into clay for subsequent static loading tests. Soil plug length of the test piles was continuously measured during installation, allowing for calculation of the incremental filling ratio. The recorded data in static loading test were reported and analyzed. The distribution of residual forces after installation and the effect on the bearing capacity were also discussed in detail. The test piles were observed to be in partially plugged condition during installation. The measured ultimate shaft resistance and total resistance of the test piles were 639 and 1180 kN, respectively. The residual forces locked in the test piles after installation significantly affected the evaluation of the axial forces, and thus the shaft and end resistances. It tended to underestimate the end resistances and overestimate the shaft resistances if the residual forces were not considered in the loading test. However, the residual forces did not affect the total bearing capacity of open-ended PHC pipe piles in this study.

Comparative embryonic development of nematodes of the genus Тrichuris (Nematoda, Trichuridae) obtained from sheep (Ovis aries)

Biological specifics of Trichuris оvis Abildgaard, 1795 and T. globulosa Linstow, 1901 parasitizing domestic sheep were analyzed enhancing the species identification of these nematode species. The embryonic development of nematodes was timed, survival of embryonic stages was determined taking into account their morphological and metric specifics in laboratory culture. Trichuris eggs were isolated from gonads of adult female nematodes collected from caeca of dissected sheep. Then the eggs were cultured at optimal temperature to the formation of eggs with mobile larvae. Six morphologically distinct stages of embryogenesis were established in T. оvis and T. globulosa nematodes. The protoplast stage lasted from the 1st to the 12th day in T. оvis and to the 18th day in T. globulosa. Blastomeric formation occurred from the 3rd to the 18th day in T. оvis and from the 3rd to the 21st day in T. globulosa. Bean-shaped embryos formed from the 6th to the 21st day in T. оvis, and from the 9th to the 30th day in T. globulosa. Tadpole-like embryos developed from the 12th to the 24th day in T. оvis and from the 18th to the 33rd day in T. globulosa. Larvae formed in eggs of T. оvis from the 18th to the 27th day, and in eggs of T. globulosa from the 21st to the 36th day. Mobile larvae formed from the 21st to the 30th day in T. оvis, and from the 30th to the 39th day in T. globulosa. At 27 °С, mature eggs with mobile larvae developed in 30 days in T. оvis and in 39 in T. globulosa. The egg survival in laboratory culture was 84.3 ± 4.2 % and 76.3 ± 1.5%, respectively. Developmental changes of metric parameters in Trichuris nematode eggs (length and width of eggs, plug length, eggshell thickness) were species-specific.

Friction plug welding acrylonitrile butadiene styrene sheets: the investigation of welding process, joint morphology and mechanical property

In this paper, friction plug welding technology was employed to join Acrylonitrile Butadiene Styrene sheets. Proper welding process was investigated and determined first, and the influence of plug diameter and length, blind hole profile and depth on joint morphology and mechanical performance was investigated subsequently. Results showed that incomplete connection was generated at the weld boundary when no chuck was utilized, and excellent bonding was produced with the employment of a chuck. Joints produced with blind holes that characterized by perpendicular base angle showed incomplete fusion at the bottom corner of the weld while defect-free joints were obtained with rounded hole base angle. Plug size and blind hole depth significantly affected the joint morphology and strength. Cavities were formed under small plug diameter, excessive plug length or large blind hole depth, and weak connection occurred when plug length was small. Joint shear strength increased with the plug diameter but decreased with the plug length. Proper increase of the hole depth slightly influenced the joint quality, but extreme hole depth caused reduced joint strength. Only joints fabricated with insufficient plug length failed with lower nugget pulling out and other spot welds failed with shear fracture.

Experimental study on the flow pattern and pressure gradient of air-water two-phase flow in a horizontal circular mini-channel

Experimental studies on the flow pattern and the pressure gradient of gas-liquid co-current two-phase flow in a mini-channel were conducted. The test section was a transparent circular channel of 1.6 mm inner diameter. The working fluids were air and water. The superficial velocities of gas and liquid were in the range of 0.025-66.300 m/s and 0.033-4.935 m/s, respectively. In the present works, the flow pattern and the pressure gradient data were obtained by analyzing the flow images captured bya high-speed camera, and by using the pressure transducer, respectively. As a result, it was found that (1) the obtained flow patterns were bubbly, plug, slug-annular, annular, and churn flows, (2) new experimental correlations on the bubble and plug lengths were proposed, whereas the lengths are the function of the homogeneous void fraction, (3) both gas and liquid superficial velocities affect proportionally to the pressure gradient, whereas it increases with the increase both of JG and JL. In addition, the obtained flow patterns are in a good agreement with that of the available flow pattern maps in the open literatures, such as, Triplett et al. (1999) and Chung and Kawaji (2004).

In-line tryptic digestion of therapeutic molecules by capillary electrophoresis with temperature control

The main purpose of the present work is to provide a fully integrated temperature control of in-line tryptic digestion in order to facilitate the quality control of polypeptidic therapeutic compounds. The in-line enzymatic reaction was performed in 100 mM bicarbonate ammonium whereas a mixture of citric acid/ε-amino caproic acid (pH 5.0 and I 75 mM) was used as a background electrolyte (BGE). After the injection of all reactants (substrate, enzyme, proteolysis buffer), a BGE plug was injected to push all reactants until a position where the capillary is thermostated. Then, the enzymatic reaction was initiated during 15 min of incubation time and finally, a voltage was applied to separate the generated proteolysis products. The methodology was developped regarding the effects of the BGE plug length and pressure on the reactants plug mixing and on the advanced of the tryptic digestion. Successful temperature control of in-line proteolysis with excellent repeatability was obtained in optimal cleavage and separation conditions.

A liquid plug moving in an annular pipe—Flow analysis

The flow in a liquid plug moving in an annular pipe is analytically solved. The interaction with the two concentric walls of the annular pipe results in two toroidal vortexes within the concentric plug. Focus is put on long plugs with aspect ratio β > 2, which have vortex circulation flow rates and volume ratio independent of the plug length. Based on the analytical results, correlations are derived for the circulation flow rates of the plug and each vortex and for the volume ratio of the two vortexes. Correlations are also developed for evaluating the radial transport of the plug flow. The friction factor for concentric plugs is a function of the aspect ratio and the radius ratio. For very long plugs with β ≫ 1, the friction factor approaches that of the fully developed continuous flow in the annular pipe.

Flow visualization of R32 in parallel-port microchannel tube

This paper presents visualization of two-phase flow of R32 in a parallel-flow microchannel tube with hydraulic diameter of 0.643 mm. Six visualization sections are installed in the facility, the same as in Li and Hrnjak (2017). Flow patterns are classified as: plug/slug, transitional, and annular flow. In plug/slug flow, a clear interface between liquid slug and vapor plug is observed. In transitional flow, the interface between slug and plug is broken and becomes a thick liquid ring and vapor bridge. In annular flow, only a liquid film is observed in the channel. The flow pattern map of R32 is reported. Mass flux changes from 50 to 300 kg-m−2s−1. The two-phase flow is generated by adding heat to subcooled refrigerant. The interface velocity and vapor plug length fraction (close to void fraction) are measured from high speed video. The velocity and vapor fraction agree to results based on a homogeneous assumption. When mass flux is 50 kg-m−2 s−1, the flow is always in plug/slug from vapor quality 0 to 1. Annular flow is observed at high quality when mass flux is higher than 100 kg-m−2 s−1. Transitional flow is observed when mass flux is higher than 150 kg-m−2 s−1, and it connects the plug/slug and annular flow patterns. Most flow pattern correlations fail to fit the measured flow pattern map. This is due to the difference in two-phase flow generation method and experimental conditions between this paper and the database used in correlations.

Flow hydrodynamics of immiscible liquids with low viscosity ratio in a rectangular microchannel with T-junction

We present an experimental study of the liquid-liquid system with extremely low viscosity ratio (10−3) in a T-shaped microchannel with 120 × 120 μm inlets and a 240 × 120 μm outlet channel. Six different flow patterns have been observed: plug, droplet, slug, throat-annular and parallel flow. A specific plug flow pattern was found where micron-sized droplets or even a jet breaks off from the rear meniscus of a plug. In addition to typical Taylor-shaped plugs the dumbbell-like plugs were observed. Flow visualization data were summarized in the flow pattern maps. Plug length and velocity were measured based on flow visualization results. It was found that the plug velocity can be fitted by power function rather than the linear function, which disagrees with experimental data at a low plug velocity. Front and tail plug surface curvature was scaled using dimensionless parameter, the flow rate ratio multiplied by Capillary number based on bulk velocity (Qd/Qc * Cabulk). Instantaneous velocity vector fields inside water plugs were measured by means of PTV technique. Different flow structures were found and discussed. As a result, it is proposed to use the values of Qd/Qc * Cabulk for distinguishing different plug shapes and circulation patterns inside the plugs.

Development of a modified partial filling method in capillary electrophoresis using two chiral plugs for the simultaneous enantioseparation of chiral drugs: Comparison with mixed chiral selector capillary electrophoresis

In this study, a chiral CE method was developed based on the partial filling technique with two chiral plugs for the simultaneous enantioseparation of some racemic drugs, including baclofen, carvedilol, cetirizine, chlorpheniramine, citalopram, fluoxetine, hydroxyzine, propranolol, tramadol, trihexyphenidyl. This method of capillary filling involves the application of two adjacent chiral plugs containing the same BGE, but with different chiral selectors in the plugs for the enantioseparation of a mixture of drugs which cannot be separated with single or mixed chiral selectors. By using this method, each plug can separate the enantiomers independently (same as a single chiral selector modified CE) and the possible interactions between the chiral selectors would be inhibited. The best results were obtained using a fused silica capillary (60cm×50μm id (50cm effective length)) with phosphate buffer (100mM, pH 3.0) containing 10mM hydroxypropyl-α/β-cyclodextrin and 10% (w/v) maltodextrin and detected by UV at 214nm. The influence of the length and order of the chiral plugs on the enantioresolution was also studied and optimized. The proposed method was compared with a mixed chiral selector-CE system with a combination of hydroxypropyl-α-cyclodextrin/hydroxypropyl-β-cyclodextrin and maltodextrin in the BGE. According to the results, the modified partial filling method is a simple and efficient method for the simultaneous chiral separation and offers appropriate migration times and resolutions compared to the results obtained from mixed chiral selector CE.

Formation of soil plug in open-ended pipe piles in sandy soils

Open-ended pipe piles are commonly used for the foundations of offshore jacket platforms, mooring piles, offshore wind turbines and, in general, for pile foundations like micro piles, etc. Driveability of open-ended piles is greatly affected by the formation of soil plug during the driving, particularly in sandy soils. In order to study the behaviour of formation of soil plug during driving, open ended model piles were driven into uniformly graded sand in a calibration chamber in the laboratory scale as well as in the field. The influence of the pile diameter, hammer energy and pile penetration depth were studied. The results of the model pile tests showed that the incremental filling ratio (IFR, which indicates the degree of plugging) during driving decreased with pile penetration and increased with increase in hammer energy. IFR has also increased with increase in pile diameter. A correlation between plug length ratio (PLR, percentage plug height with respect to total penetration) and IFR is proposed based on the laboratory experiments.

Water-in-oil emulsification in a bifurcated tree-like network: Flow distribution properties and their impact on the emulsion polydispersity

This paper presents a numerical study on the water-in-oil emulsification process through the parallelization of micro/mini-channels. Firstly, the single-phase fluid flow distribution uniformity in the bifurcated tree-like fluidic network is discussed. Secondly, the separate roles of the oil viscosity and the interfacial tension on the plug details are clarified. Finally, the impact of flow distribution non-uniformity among the parallel mini-channels on polydispersity of the produced emulsion is evaluated by modelling.The obtained results show that for bifurcated tree-like fluidic network, the single phase flow distribution is the flow distribution non-uniformity increases linearly with the increasing mean Rech once a transitional Re is reached. The water plug length and volume increase with the increasing interfacial tension and the decreasing oil viscosity under our tested conditions. Correcting factors relevant to the modified liquid properties have to be added in the predictive correlations for plug length and volume. For water-in-oil emulsification in parallel channels, its polydispersity Pw is affected by the single phase flow distribution uniformity, the total water/oil flow-rate ratio and most importantly by the flow-rate ratio distribution non-uniformity. An empirical correlation has been proposed to predict the emulsion Pw based on these influencing factors.

Dynamics of a liquid plug in a capillary tube under cyclic forcing: memory effects and airway reopening

In this paper, we investigate both experimentally and theoretically the dynamics of a liquid plug driven by a cyclic periodic forcing inside a cylindrical rigid capillary tube. First, it is shown that, depending on the type of forcing (flow rate or pressure cycle), the dynamics of the liquid plug can either be stable and periodic, or conversely accelerative and eventually leading to plug rupture. In the latter case, we identify the sources of the instability as: (i) the cyclic diminution of the plug viscous resistance to motion due to the decrease in the plug length and (ii) a cyclic reduction of the plug interfacial resistance due to a lubrication effect. Since the flow is quasi-static and the forcing periodic, this cyclic evolution of the resistances relies on the existence of flow memories stored in the length of the plug and the thickness of the trailing film. Second, we show that, contrary to unidirectional pressure forcing, cyclic forcing enables breaking of large plugs in a confined space although it requires longer times. All the experimentally observed tendencies are quantitatively recovered from an analytical model. This study not only reveals the underlying physics but also opens up the prospect for the simulation of ‘breathing’ of liquid plugs in complex geometries and the determination of optimal cycles for obstructed airways reopening.

Incremental filling ratio of pipe pile groups in sandy soil

Formation of a soil plug in an open-ended pile is a very important factor in determining the pile behavior both during driving and during static loading. The degree of soil plugging can be represented by the incremental filling ratio (IFR) which is defined as the change in the plug length to the change of the pile embedment length. The experimental tests carried out in this research contain 138 tests that are divided as follows: 36 tests for single pile, 36 tests for pile group (2x1), 36 tests for pile group (2x2) and 30 pile group (2x3). All tubular piles were tested using the poorly graded sand from the city of Karbala in Iraq. The sand was prepared at three different densities using a raining technique. Different parameters are considered such as method of installation, relative density, removal of soil plug with respect to length of plug and pile length to diameter ratio. The soil plug is removed using a new device which is manufactured to remove the soil column inside open pipe piles group installed using driving and pressing device. The principle of soil plug removal depends on suction of sand inside the pile. It was concluded that the incremental filling ratio (IFR) is changed with the changing of soil state and method of installation. For driven pipe pile group, the average IFR for piles in loose is 18% and 19.5% for L/D=12 and 15, respectively, while the average of IFR for driven piles in dense sand is 30% and 20% for L/D=12 and L/D=15 respectively. For pressed method of pile installation, the average IFR for group is zero for loose and medium sand and about 5% for dense sand. The group capacity increases with the increase of IFR. For driven pile with length of 450 mm, the average IFR % is about 30.3% in dense sand, 14% in medium and 18.3% for loose sand while when the length of pile is 300 mm, the percentage equals to 20%, 17% and 19.5%, respectively.

Analyses of Sampling Disturbance of the Lunar Surface in Direct Push Sampling Method

The study of direct push sampling characteristics forms the theoretical basis for deep sampling tool design. In this paper, a ground test of the direct push sampling was carried out to analyze three influencing factors: tube diameter; friction coefficient; and soil plug length. Using the discrete element method software, EDEM, a lunar subsurface direct push sampling model was established. We propose a vortex structure of the particle displacement field in the sampling tube and establish a connection between the three influencing factors and the structure disturbance of the soil plug. The EDEM simulation revealed the microscopic mechanism of penetration sampling disturbance. The results show that the soil plug in the compressive state had a small disturbance and a high degree of sequence retention and that the internal stress was changed compared to that in the in-situ state. The structure disturbance of the soil plug in the stick-slip state was large, while the parts of the soil plug that are away from the center line of the tube were in disorder. In the center line of the tube, the in-situ sequence state was gradually restored with the increase in tube diameter or decrease in soil plug length. Increasing the friction coefficient would change the soil plug from the compression state to the stick-slip or adhesion state. In case of the stick-slip state or adhesion, reducing the diameter of the tube or increasing the length of the soil plug would change the soil plug from the stick-slip state or adhesion state to the compression state.

Experimental study of ionic liquid-water flow in T-shaped microchannels with different aspect ratios

Flow regimes of immiscible ionic liquid - water flow in T-shaped microchannels with 160 um hydraulic diameter and 1:2 and 1:4 aspect ratios are experimentally studied in the present work. Plug length and velocity were measured using high-speed visualization of the flow. Flow pattern maps were drawn for two channels. Parallel flow was shown to prevail for 1:4 aspect ratio channel in comparison to 1:2.

Detachment velocity: A borderline between different types of particulate plugs

Shaul & Kalman (2014–2015) defined three different types of plugs (Plug-I, II and III) of different particulate materials for dense phase pneumatic conveying. The Present experimental study is undertaken to determine the borderline between Plug-I and the other type of plugs. The borderline is established by using the concept of detachment velocity of the particles from the front of the plug. For the current study, thirty three particulate materials have been tested having the Archimedes number (Ar) in the range of 10−3 to106. The experiments conducted in three transparent Plexiglas pipes of diameters 1in., 2in. and 3in. For each experiment, a single artificial plug of type I of varying length in the range of 10–100cm was inserted into the test section of 1.5m length. Further, as the plug flow is a low velocity phenomenon, the Reynolds number (Re) during experimentation, is varied in the range of 10−3 to 102. The results of the experiments show that for the particulate materials with Ar>102, first the phenomenon of detachment occurs at a corresponding velocity and on further increasing the flow rates the plug dissembled. The variation of the detachment velocity is found to be a power function of the Ar number (for Ar>102), whereas, the detachment velocity is found to be independent of the pipe diameter and plug length. For materials with Ar<102 no detachment of the particles from the plug front is observed and the plug starts to move as Plug-I at a critical air flow-rate and a critical plug length corresponding to respective material.

Experimental and numerical hydrodynamic studies of ionic liquid-aqueous plug flow in small channels

The hydrodynamic characteristics of liquid-liquid plug flow were studied in microchannels with 0.2 and 0.5mm ID both experimentally and numerically. For the experiments high speed imaging and bright field micro-Particle Image Velocimetry were used, while the numerical simulations were based on the volume-of-fluid (VOF) method. The two immiscible liquids were a 1M HNO3 aqueous solution which formed the dispersed plugs and a mixture of 0.2M n-octyl(phenyl)-N,N-diisobutylcarbamoylmethyphosphine oxide (CMPO) and 1.2M Tributylphosphate (TBP) in the ionic liquid 1-butyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]amide ([C4min][NTf2]). The thickness of the film surrounding the plugs, and the plug velocity and length were measured and compared against literature correlations. For the cases studied (0.0224<Ca<0.299) it was observed that the liquid film was largely affected by the changes in the shape of the front cap of the plug. The plug length was affected by both the Capillary number and the ratio of the aqueous to ionic liquid phase flow rates while the plug volume depended on the channel diameter and the mixture velocity. The numerical simulations showed that, in agreement with the measurements, a parabolic velocity profile develops in the middle of the plugs while the circulation patterns in the plug are affected by the channel size. The pressure profile along the channel with a series of plugs and slugs was predicted numerically while the pressure drop agreed well with a correlation which included the dimensionless slug length and the ratio Ca/Re.

Insights into head-column field-amplified sample stacking: Part II. Study of the behavior of the electrophoretic system after electrokinetic injection of cationic compounds across a short water plug

Part I on head-column field-amplified sample stacking comprised a detailed study of the electrokinetic injection of a weak base across a short water plug into a phosphate buffer at low pH. The water plug is converted into a low conductive acidic zone and cationic analytes become stacked at the interface between this and a newly formed phosphoric acid zone. The fundamentals of electrokinetic processes occurring thereafter were studied experimentally and with computer simulation and are presented as part II. The configuration analyzed represents a discontinuous buffer system. Computer simulation revealed that the phosphoric acid zone at the plug-buffer interface becomes converted into a migrating phosphate buffer plug which corresponds to the cationically migrating system zone of the phosphate buffer system. Its mobility is higher than that of the analytes such that they migrate behind the system zone in a phosphate buffer comparable to the applied background electrolyte. The temporal behaviour of the current and the conductivity across the water plug were monitored and found to reflect the changes in the low conductivity plug. Determination of the buffer flow in the capillary revealed increased pumping caused by the mismatch of electroosmosis within the low conductivity plug and the buffer. This effect becomes elevated with increasing water plug length. For plug lengths up to 1% of the total column length the flow quickly drops to the electroosmotic flow of the buffer and simulations with experimentally determined current and flow values predict negligible band dispersion and no loss of resolution for both low and large molecular mass components.