Straight Capillaries Research Articles

Effect of interfacial mass transfer on the dispersion in segmented flow in straight capillaries

The effect of interfacial mass transfer on the extent of dispersion in liquid‐liquid segmented flow in straight capillaries is studied. In the absence of interfacial mass transfer, dispersion coefficient was seen to go through a minimum with increasing flow rates. In the presence of mass transfer, physicochemical properties of both the phases and slug lengths were seen to vary along the capillary length. The extent of dispersion was always higher in the presence of interfacial mass transfer. The predictions using axial dispersion model deviated noticeably for larger capillaries as the model does not account for varying buoyancy, dynamic contacting, and Marangoni convection. Simulations of a first‐order interfacial reaction considering varying slug lengths showed a significant change in optimum operating parameters than the conventional approach. A special case of “drop‐on‐demand” type of controlled two‐phase flow in capillaries was also studied. © 2015 American Institute of Chemical Engineers AIChE J, 61: 4294–4308, 2015

Enhancing separation in short‐capillary electrophoresis via pressure‐driven backflow

Electrophoresis 2015, 36, 1549–1554. DOI: 10.1002/elps.201500013 Pressure-driven backflow is an attractive method to improve CZE separation resolution via counterbalancing the EOF. In this study, we describe a new method to generate steady backflow in a short capillary via a tapered capillary tip, which can be easily fabricated by heating a straight capillary while stretching it with a constant force. Significant improvement of the CZE separation of AAs is achieved using the tapered capillary with effective separation length of 5 cm. The present method presents good run-to-run repeatability and capillary-to-capillary reproducibility, and has merits in its simple and easy-to-operate design, which could be useful in further miniaturization of the CZE technique.

Enhancing separation in short-capillary electrophoresis via pressure-driven backflow.

We present a novel easy-to-operate and efficient method to improve the separation efficiency in short-capillary electrophoresis by introducing steady backflow to counterbalance electro-osmotic flow without the use of any external pressure. The backflow was easily generated by tapering the capillary end, which was achieved by heating a straight capillary and stretching it with a constant force. We investigated the net fluidic transport rate under different tip lengths and separation voltages. Good run-to-run repeatability and capillary-to-capillary reproducibility of the present method were obtained with RSD less than 1.5%, indicating the stability of the fluid transport rate in the tapered capillary, which ensures the quantification and repeatability of capillary zone electrophoresis (CZE) analysis. Enhanced separation of the tapered short capillary electrophoresis was demonstrated by CZE analyzing amino acids and positional isomers. Baseline separations were achieved in less than 60 s using a tapered capillary with the effective length of 5 cm, while no separation was achieved using a normal capillary without a tapered tip. The present study provides a promising method to use pressure-driven backflow to enhance separation efficiency in short-capillary electrophoresis, which would be of potential value in a wide application for fast analysis of complex samples.

Infiltration into Two-Layered Soil: The Green–Ampt and Averyanov Models Revisited

Infiltration into a two-layered soil (continuum scale) is studied by the Green–Ampt (GA) model where the rate of infiltration (wetting front propagation) is a non-monotonic and discontinuous function of time. Both a constant ponding depth and a ponding level falling due to evaporation and infiltration are studied theoretically and in column experiments. The triads of saturated conductivity, porosity and front pressure in the two zones, as well as gravity, control vertical infiltration. Another model on the scale of a straight cylindrical capillary uses the Averyanov regime of a film flow, modified to include a front which is a quarter of a torus, rather than a spherical cap in a standard Washburn–Lukas model. The rate of front propagation is controlled by the Newtonian viscosity, tube-film sizes, surface tension, contact angle and gravity. For both scales, Cauchy problems for ODEs with respect to the front position are solved by computer algebra integration. In the field, pedon description and textural analysis of sedimentation-controlled layering are done. Of particular note is the thick cake deposited from a flash flood water pulse, which has very low permeability and can greatly inhibit infiltration. The infiltration rates measured by tension infiltrometers fluctuate, which is attributed to the mosaic and layered special distribution of hydraulic and capillary properties of the accrued sediments. Falling ponding depth laboratory experiments were conducted in four columns with a coarse substratum (sand) subjacent to a layer of thoroughly homogenized repacked dam silt. Imbibition front stopped at the interface between two texturally contrasting strata and the “waiting time” of the capillary barrier breakthrough was measured, as well as further oscillations of the infiltrations rate.

MRI investigation of water–oil two phase flow in straight capillary, bifurcate channel and monolayered glass bead pack

The study of immiscible fluid displacement between aqueous-phase liquids and non-aqueous-phase liquids in porous media is of great importance to oil recovery, groundwater contamination, and underground pollutant migration. Moreover, the attendant viscous, capillary, and gravitational forces are essential to describing the two-phase flows. In this study, magnetic resonance imaging was used to experimentally examine the detailed effects of the viscous, capillary, and gravitational forces on water–oil flows through a vertical straight capillary, bifurcate channel, and monolayered glass-bead pack. Water flooding experiments were performed at atmospheric pressure and 37.8°C, and the evolution of the distribution and saturation of the oil as well as the characteristics of the two-phase flow were investigated and analyzed. The results showed that the flow paths, i.e., the fingers of the displacing phase, during the immiscible displacement in the porous medium were determined by the viscous, capillary, and gravitational forces as well as the sizes of the pores and throats. The experimental results afford a fundamental understanding of immiscible fluid displacement in a porous medium.

Vascular Pattern Analysis for the Prediction of Clinical Behaviour in Pheochromocytomas and Paragangliomas

Pheochromocytomas (PCCs) are neuroendocrine tumors arising from chromaffin cells of the adrenal medulla. Related tumors that arise from the paraganglia outside the adrenal medulla are called paragangliomas (PGLs). PCC/PGLs are usually benign, but approximately 17% of these tumors are malignant, as defined by the development of metastases. Currently, there are no generally accepted markers for identifying a primary PCC or PGL as malignant. In 2002, Favier et al. described the use of vascular architecture for the distinction between benign and malignant primary PCC/PGLs. The aim of this study was to validate the use of vascular pattern analysis as a test for malignancy in a large series of primary PCC/PGLs. Six independent observers scored a series of 184 genetically well-characterized PCCs and PGLs for the CD34 immunolabeled vascular pattern and these findings were correlated to the clinical outcome. Tumors were scored as malignant if an irregular vascular pattern was observed, including vascular arcs, parallels and networks, while tumors with a regular pattern of short straight capillaries were scored as benign. Mean sensitivity and specificity of vascular architecture, as a predictor of malignancy was 59.7% and 72.9%, respectively. There was significant agreement between the 6 observers (mean κ = 0.796). Mean sensitivity of vascular pattern analysis was higher in tumors >5 cm (63.2%) and in genotype cluster 2 tumors (100%). In conclusion, vascular pattern analysis cannot be used in a stand-alone manner as a prognostic tool for the distinction between benign and malignant PCC, but could be used as an indicator of malignancy and might be a useful tool in combination with other morphological characteristics.

An experimental study of the flow of LPG as refrigerant inside an adiabatic helical coiled capillary tube in vapour compression refrigeration system

This paper presents an experimental investigation for the flow of liquefied petroleum gas (LPG) as a refrigerant inside an adiabatic helically coiled capillary tube in vapour compression refrigeration system. The effect of various geometric parameters and operating conditions like capillary tube inner diameter, length of capillary tube, coil diameter and different inlet subcoolings on the mass flow rate of LPG through the helical coiled capillary tube geometry has been investigated. It has been established that the coil diameter significantly influences the mass flow rate of LPG through the adiabatic helical capillary tube. It has been concluded that the effect of coiling of capillary tube reduces the mass flow rate by 5–12 % as compared to those of the straight capillary tube operating under similar conditions. The data obtained from the experiments are analyzed and a dimensionless correlation has been developed. The proposed correlation predicts that more than 90 % of experimental data which is in agreement with measured data in an error band of ±10 %.

Ion guiding in curved glass capillaries

Straight and curved glass capillaries were tested for the guiding of 8keV Ar8+ ion beams. The straight capillary was about 50mm long and 0.87mm/1.1mm in inner/outer diameter. One of the two curved capillaries was similar, but was curved with a 270mm radius. The other was 53mm long, had diameters of 2.34mm/2.99mm, and was curved with a 150mm radius. The corresponding bending angles of the two curved capillaries were 9.6° and 17.5°, respectively. Transmission through the straight capillary disappeared when the tilt angle was larger than 5°. The curved capillaries guided the ion beams into their corresponding bending angles, which were much larger than 5°, with transmission efficiencies of a few tens percent. This demonstrates the possibility of developing a new scheme of simple small beam deflectors and related beam optics.

Mathematical modeling of CO2 separation from gaseous-mixture using a Hollow-Fiber Membrane Module: Physical mechanism and influence of partial-wetting

The present study describes a steady-state phenomenological model for CO2 separation via reactive absorption into aqueous Diethanolamine (DEA) solution using a micro-porous Poly-propylene (PP) Hollow-Fiber Membrane Module (HFMM). The developed model is based on the fundamental mechanisms of molecular diffusion, bulk convection and liquid-phase chemical reaction, and simultaneously accounts for the consequences of ‘partial-wetting’ phenomenon. Furthermore, a physically-consistent wetting mechanism has been formulated assuming that the membrane pores may be modeled as a bundle of straight cylindrical capillaries with distinct radii (characterized by the membrane pore-size distribution) and equal lengths, while keeping in mind the various pore-scale micro-physical phenomena. Under the simplifying parameterizations of the Finite-Volume Method (FVM), the source-code for discretized equations was compiled and implemented using C++ Language for a co-current module operation with aqueous DEA solution flowing inside the fiber-lumen and CO2–N2 gaseous mixture passing through the shell-side. A Benchmarking Analysis revealed an excellent agreement between the model predictions and the experimental data reported in open-literature, thereby validating the current model formulation, and rendering it fundamentally relevant with respect to the wetting-phenomenon. In addition, the module performance in terms of CO2 flux, Overall Mass-Transfer Coefficient (MTC), and Removal-Efficiency, has been systematically analyzed pertaining to the physical influence of other operating variables such as absorbent concentration, hydrodynamics, pressure, temperature, and membrane characteristics. From a modeling standpoint, it may be concluded that the present model successfully captures various observations vis-à-vis the process of CO2 separation using micro-porous HFMMs, reported previously in the literature. Moreover, for a given gas-phase hydrodynamics, the current set of results suggest the existence of a unique liquid-phase hydrodynamic regime, bounded by a minimum and a maximum permissible pressure, under which the module can be effectively operated without any dispersive losses. Besides, the currently developed model has been demonstrated to explain the reduction in CO2 flux over time by allowing for morphological changes, including an enlargement in the average pore-size and a broadening of the pore-size distribution.

Transient modeling of fiber spinning with filament pull-out

Flow instabilities of wet-spun fibers in the form of draw resonance can result in radius fluctuations which impose limitations on either fiber quality or production rate. Also, at high winding velocities, if the fluid strength is sufficiently high, a filament can pull out of the capillary. Filament pull-out complicates the stability analysis of fiber spinning in the sense that the upstream boundary conditions now depend on the position in the spinneret. In addition, the filament length varies in time. Intuitively, one would expect that including filament pull-out will stabilize the spinning process since the change in filament length adjusts the spinning force to result in a process similar to spinning with a constant take-up force, which is always stable. However, from a linear stability analysis on a thin filament fiber spin model including filament pull-out, we obtained the least stable solution in a straight capillary with minimal restriction on the movement of the detachment position, see van der Walt et al. (2012) [1]. In this paper we extend the stability analysis to a fully axisymmetric transient isothermal fiber spin model including filament detachment from the capillary wall using the eXtended Pom-Pom (XPP) constitutive model. Using finite elements, we develop a numerically efficient algorithm for the dynamics of the detachment point. A comparison between the stability results of the axisymmetric and the thin filament model shows that the axisymmetric model is more stable than the thin filament pull-out model but less stable than the thin filament fixed length model for the same De (Deborah) number. We are also not able to confirm from the axisymmetric model the assumption of the force being a function of the detachment position in the thin filament model. Revisiting the integral momentum balance at the detachment point derived by Bulters and Meijer (1990) [2] we find that their force balance is not valid. There is a transient region near the detachment position from the integrated normal stress to the spinning force.

Experimental investigation and numerical simulation of choked refrigerant flow through helical adiabatic capillary tube

This paper presents a drift flux model and experimental study of choked refrigerant flow through both straight and helical adiabatic capillary tubes. The conservation equations of mass, energy, and momentum are solved using the fourth order Runge-Kutta method. This model is validated by previously published experimental data and also by test results performed and presented in this work for R-134a with average error of 5.5%. The effect of capillary tube inner diameter, length, relative roughness and coil diameter, and also various test conditions such as inlet pressure, inlet temperature, and sub-cooling degree of refrigerants are investigated. Critical mass flux variation, pressure distribution and temperature variation are obtained experimentally as well as vapor quality, vapor velocity and void fraction variation by numerical simulation. The results show that mass flux reaches a maximum amount at a specific value of evaporator pressure in choked conditions and also it is decreased by increasing the length of capillary tube. Moreover, critical mass flux increases by increasing of the tube inner diameter, condensation temperature and refrigerant degree of sub-cooling.

Transmission of fast highly charged ions through straight and tapered glass capillaries

The transmission of 1 and 3 MeV protons through a borosilicate straight glass capillary and a tapered glass capillary was investigated. The straight capillary had a diameter of ∼0.18 mm and a length of ∼14.4 mm, while the tapered capillary had an inlet diameter of ∼0.71 mm, an outlet diameter of ∼0.10 mm and a length of ∼28 mm. The results show that the 1 and 3 MeV protons traverse through both samples without energy loss, while the tapered capillary showed better transmission than the straight capillary.

Numerical simulation and experimental analysis of refrigerants flow through adiabatic helical capillary tube

In the present study, two-phase refrigerant flow is simulated using drift flux model for straight and helical capillary tubes. The conservation equations of mass, energy and momentum are solved using the 4th order Runge–Kutta method. This model is validated by previously published experimental and numerical results and also by experimental results presented in this work. The effect of various parameters such as inlet pressure, inlet temperature, sub-cooling degree, and geometric dimensions are studied. The results of the present study show that for the same length and under similar conditions, mass flux through helical capillary tube with coil diameter of 40 mm are about 11% less than that through the straight tube, where the helical tube length is about 14% shorter than the straight one for the same refrigerant mass flux.

Taylor Dispersion Analysis in Coiled Capillaries at High Flow Rates

Taylor Dispersion Analysis (TDA) has been performed for analytes moving at high flow rates in long, coiled capillaries. A thin injection zone of the analyte is stretched by the flow and final distribution of concentration of the analyte at the end of the capillary has the gaussian shape. The high flow rates in coiled capillary generate vortices. They convectively mix the analyte across the capillary. This mixing reduces the width of the gaussian distribution several times in comparison to the width obtained in a straight capillary in standard TDA. We have determined an empirical, scaling equation for the width as a function of the flow rate, molecular diffusion coefficient of the analyte, viscosity of the carrier phase, internal radius of the cylindrical capillary, and external radius of the coiled capillary. This equation can be used for different sizes of capillaries in a wide range of parameters without an additional calibration procedure. Our experimental results of flow in the coiled capillary could not be explained by current models based on approximate solutions of the Navier-Stokes equation. We applied the technique to determine the diffusion coefficients of the following analytes: salts, drugs, single amino acids, peptides (from dipeptides to hexapeptides), and proteins.

FLASHING LIQUID JETS IN LOW-PRESSURE ENVIRONMENT

In the present paper, highly expanded flashing liquid jets in a low-pressure environment are studied experimentally, particularly focusing upon the physics associated with liquid flashing regimes. A long, straight stainless steel capillary with an inner diameter of 0.23 mm and a length of 17.0 mm is used as the nozzle, which is connected with a syringe. Through a solenoid valve, a test vessel is connected with a vacuum chamber with a volume about 800 times bigger than that of the test vessel, in order to keep constant pressure inside the test vessel throughout every experimental run. Distilled water of about 1 mL is filled into the syringe at first, while the syringe is open to the ambient. Then, opening the solenoid valve, the air inside the test vessel will be evacuated quickly, resulting in a quick depressurization and a low backpressure inside the test vessel. The water in the syringe is then driven by the difference between the ambient pressure and the backpressure to form a highly expanded flashing liquid jet into the test vessel. For the case of low initial temperature and high backpressure, there is no evaporation, and then the flow of the liquid jet from the nozzle exit section remains intact and follows a straight path. On the other hand, if the initial temperature is high and/or the backpressure is low enough to lead a superheated exit condition, evaporation will take place, irregular evaporation waves around the liquid core are visible, and the jet shattering occurs. On further decreasing the backpressure, the liquid jet shatters giving rise to a cloud of droplets with a spray angle usually bigger than 90°, indicating a large number of nucleation sites and rapid bubble growth. It is also shown that there is flow choking behavior as the flow rate becomes constant and is insensitive to pressure reduction below some backpressure threshold.

Central neurocytoma case report: cytological and histological correlation

Central neurocytomas are rare intraventricular neoplasms of neu-ronal origin with typical radiological, histological and immuno-histochemical features. They characteristically occur in the lateral ventricular location in young to middle aged adults. Most cases have favourable prognosis with some tumours showing recurrence and more aggressive clinical course. Intraoperative cytomorpho-logical and frozen section diagnosis can be difficult due to resemblance to oligendroglioma, ependymoma and non-Hodgkin lym-phoma. We describe a case of a 24-year-old man who presented with dizzy spells and subsequently a grand mal seizure. Neuroim-aging revealed a 36 mm solid-cystic mass within the anterior horn and body of the right lateral ventricle. The cytological and histo-pathological examination showed a cellular monomorphic round cell neoplasm comprising sheets of uniform small to medium sized cells with round to oval nuclei and evenly distributed stippled chromatin. The cytoplasm was scant eosinophilic with indistinct borders. The background was formed by neuropil and delicate short straight capillaries. Multiple small calcospherites were present. The final diagnosis was confirmed on immunohistochemistry. The cytological and histological findings will be described and the differential diagnosis and prognostic factors of central neurocy-toma will be discussed.

A Dimensionless Capillary Pressure Function for Imbibition Derived From Pore-Scale Modeling in Mixed-Wet-Rock Images

Summary It has been demonstrated experimentally that Leverett's J-function yields almost unique dimensionless drainage capillary pressure curves in relatively homogeneous rocks at strongly water-wet conditions, whereas for imbibition at mixed-wet conditions, it does not work satisfactorily because the permeability dependency on capillary pressure has been reported to be weak. The purpose of this study is to formulate a new dimensionless capillary pressure function for mixed-wet conditions on the basis of pore-scale modeling, which could overcome these restrictions. We simulate drainage, wettability alteration, and imbibition in 2D rock images by use of a semianalytical pore-scale model that represents the identified pore spaces as cross sections of straight capillary tubes. The fluid configurations occurring during drainage and imbibition in the highly irregular pore spaces are modeled at any capillary pressure and wetting condition by combining the free-energy minimization with an arc meniscus (AM)-determining procedure that identifies the intersections of two circles moving in opposite directions along the pore boundary. Circle rotation at pinned contact lines accounts for mixed-wet conditions. Capillary pressure curves for imbibition are simulated for different mixed-wet conditions in Bentheim sandstone samples, and the results are scaled by a newly proposed improved J-function that accounts for differences in formation wettability induced by different initial water saturations after primary drainage. At the end of primary drainage, oil-wet-pore wall segments are connected by many water-wet corners and constrictions that remain occupied by water. The novel dimensionless capillary pressure expression accounts for these conditions by introducing an effective contact angle that depends on the initial water saturation and is related to the wetting property measured at the core scale by means of a wettability index. The accuracy of the proposed J-function is tested on 36 imbibition capillary pressure curves for different mixed-wet conditions that are simulated with the semianalytical model in scanning-electron-microscope (SEM) images of Bentheim sandstone. The simulated imbibition capillary pressure curves and the reproduced curves, based on the proposed J-function, are in good agreement for the mixed-wet conditions considered in this study. The detailed behavior is explained by analyzing the fluid displacements occurring in the pore spaces. It is demonstrated that the proposed J-function could be applied to mixed-wet conditions to generate a family of curves describing different wetting states induced by assigning different wetting properties on the solid surfaces or by varying the initial water saturation after primary drainage. The variability of formation wettability and permeability could be described more accurately in reservoir-simulation models by means of the proposed J-function, and hence the opportunity arises for improved evaluation of core-sample laboratory experiments and reservoir performance.

The effect of temperature on guiding of slow highly charged ions through a mesoscopic glass capillary

We present first temperature dependent transmission measurements of slow highly charged ions through a single, straight Duran glass capillary with a high aspect ratio. By changing the temperature of the glass capillary the electrical conductivity of the Duran can be varied by several orders of magnitude. This held the promise to investigate the effect of conductivity on particle transport (build-up and removal of charge patches) through capillaries in more details.

Numerical simulation of coiled adiabatic capillary tubes in CO2 transcritical systems with separated flow model including metastable flow

A separated flow model of coiled adiabatic capillary tube for CO2 considering metastable flow region is presented. In the case of straight capillary, different friction factors are compared with each other, the model using Churchill and Lin correlations gives a deviation of −1.8% compared with the experimental data for CO2. Three different friction factor correlations (Schmidt, M&N and M&N modified) are discussed for coiled capillary tube. The results show that the M&N modified friction factor gives the best reasonable prediction with a deviation of 4% compared with the experimental data for R22. The discrepancy between the capillary tube length calculated with the separated flow model and that calculated with homogeneous flow model is about 2–7% for the chosen conditions. The mass flow rate for CO2 increases about 7% when the coiled diameter changes from 40 mm to 600 mm.

Laminar flow meter with straight glass capillary

The Center for Measurement Standards (CMS) developed a laminar flow meter (LFM) as a transfer standard. This LFM consists of a single, straight glass capillary or multiple straight glass capillaries connected in parallel. Two gauges and one thermometer measure the inlet/outlet pressure and inlet temperature, respectively, and the differential pressure was restricted to between 2 kPa and 100 kPa. The glass capillaries were manufactured by laser machining, which resulting in consistent inner diameter and straight flow path. Characteristics of the glass material also prevented the capillary from bending during installation. The LFMs were calibrated against the CMS piston prover primary standard and the calibration data were fitted using a theoretical LFM model and a 2nd order polynomial. The turndown ratio of this approach was higher than 20 and the residuals were within 0.11%. The reproducibility/repeatability within 0.03% indicated that this LFM could be used as a transfer standard. Measurement with dry air demonstrated that these four LFE meters could span flows from 0.8 to 986 µmol/s within the deviation of ± 0.15% (1µmol/s is 1.3 cm3/min at 0°C and 101.325 kPa). Additional measurement with nitrogen demonstrated the feasibility of measurement with multiple gases.