Critical temperature in PVC melts detected by rheological measurements

The shear flow of PVC is analyzed under conditions similar to those of industrial processing. The existence of two mechanisms of flow is confirmed by the presence of two activation energies of flow and by change with temperature of the exponent “n” in the equation σ₂₁ = Kγⁿ. The influence of molecular weight on the critical temperature T_c, separating these different flow regions is considered.     

Modeling of combined electroosmotic and capillary flow in microchannels

In the present study, theoretical model for the transient response of a capillary flow under the combined effects of electroosmotic and capillary forces at low Reynolds number is presented. The governing equation is derived based on the balance among the electrokinetic, surface, viscous and gravity forces. A non-dimensional transient governing equation for the penetration depth as a function of time is obtained by normalizing the viscous, gravity and electroosmotic forces with surface tension force. A new non-dimensional group for the electroosmotic force, E_o, is obtained through the non-dimensional analysis. This new non-dimensional group is a representation of combined electroosmosis and surface tension, i.e., capillarity. The numerical solution of governing equation is obtained to study the effect of different operating parameters on the flow front transport. In a combined flow, it is observed that the flow with positive and low negative magnitude E_o numbers, the attainment of equilibrium penetration depth is similar to a capillary flow. In case of high negative magnitude E_o numbers, complete filling of the channel is observed. The electrolyte with lower permittivity delays the progress of the flow front whereas a large EDL transports the electrolyte quickly. Higher viscous and gravity forces also delay the transport process in the combined flow. This model suggests that in combined flow the electrokinetic parameters also play an important role on the capillary flow and experiments are required to confirm this electrokinetic effect on capillary transport.     

Generation of Water-In-Oil-In-Water (W/O/W) Double Emulsions by Microfluidics

Novel compartment microparticles prepared with double emulsion droplets as templates provide a protected internal space for material encapsulation. The effect of three-phase flow rate on the micro-droplet generation of double emulsion mechanism is available for reference to produce precise size and highly monodisperse particles. The influence of three-phase flow rate on the formation mode and size of the emulsion droplets is investigated by combination of experiment and numerical simulation. The size of compound droplets decreases and frequency increases with the increasing outer fluid flow rate. The monodispersity of the double emulsion reduces due to transition from dripping to narrowing jetting regime. Outer droplet size increases with the increasing flow rate of the middle fluid, whereas inner droplet size is the opposite. The frequency increases and then stabilizes, which leads to a widening regime. When Q₂/Q₁ > 6, the multi-core type double emulsion droplets are produced. Droplet coalescence occurs when surfactants is not involved. As Q₁ increases, there is an increasing tendency for inner drop size. The outer drop size is proportional to the sum of the inner and middle flow rate, and that is irrelevant to Q₁/Q₂. For drop size, the ratio of core-shell and internal structure is precisely controlled by adjusting three-phase flow rate respectively.     

Continuous on-line feedback based flow titrations. Complexometric titrations of calcium and magnesium

The methodology of continuous feedback-based flow titrations and the principle of compensating errors [Anal. Chem. 72 (2000) 4713; Anal. Chim. Acta 435 (2001) 289] were applied to the determination of calcium and magnesium ions with EDTA. The flow of the titrant, EDTA, varied linearly in response to a controller output voltage while the total flow (F_T, the sum of the metal ion sample flow and the titrant flow) was held constant. The sample was pre-doped with a metal ion indicator; the status of the indicator color in the mixed stream was monitored by an optical detector and was used for governing the controller output as well as for interpreting the results of the titrations. The titrant flow initially ramped upward linearly. As a change in the color corresponding to the equivalence point was sensed by the detector, the controller output (instantaneous value V_H) reversed its ramp direction, thus decreasing the titrant flow linearly at the same ramp rate. When the predefined absorbance corresponding to the equivalence point was sensed again, the controller voltage (instantaneous value V_L) was ramped in reverse once more, going upward. Because of the lag time between a change in the controller output and its effect being sensed by the detector, the controller voltage corresponding to the actual equivalence point was the average of V_H and V_L. Continuous sensor-governed operation of the controller resulted in a triangular waveform. The mean of this waveform during any cycle gives the equivalence point controller voltage V_E. This principle allowed true titrations with good reproducibility (0.2-0.7% R.S.D.) and throughput (33-42 s per titration).     

Dilute gravity flows: A phenomenological model in thin layer theory

We present a simple model for the equations of the motion of turbidity flows. The flow is treated as a deformable geometrical object, parametrized by four characteristic quantities linked to the flow: U, the mean motion velocity of the flow object; l, its length; h, its height; φ, the particles' volumetric concentration. To characterise their temporal evolution, we assume that the gravity flow of a finite volume of particulate mixture reflects the balance between the driving gravity force, the turbulent friction, the spreading due to pressure forces, the incorporation of the ambient fluid, and the deposition and/or the erosion of particles. Special emphasis is placed on the search for analytical solutions over long periods. The study shows the evolution of solutions for three physical cases and includes comparison with numerical and analogical experiments.     

Ein gesteuerter dynamischer Titrierautomat mit konduktometrischer Indizierung

The reagent solution (concentration c) is fed with constant flow rate w to a mixing chamber to which at the same time the sample solution (sample concentration x) is fed with a linearly increasing flow rate v=kt. After passing through a heat exchanger, the thermostated reaction mixture reaches a conductivity flow cell. The recorded conductivity curves are identical with the analoguous diagrams obtained by conductometric batch titrations. Thirty titrations per hour are performed automatically. The standard deviation is ±0.3 %. The sample amount does not have to be measured.     

Axial dispersion coefficient in high-speed counter-current chromatography

Experimental measurements of axial dispersion coefficients in high-speed counter-current chromatography have been carried out in the single-phase and two-phase modes. Axial dispersion coefficients were calculated from the residence time distribution curve (or the elution profile). The experimental data obtained were used to develop a model involving Peclet number Pe, Reynolds number and the ratio of flow velocity u to linear angular velocity u_θ for predicting the axial dispersion coefficient. Furthermore, the models obtained from the single-phase and two-phase modes were compared, and a counterintuitive phenomenon was found in that the effects of the flow rate and the rotation speed on the axial dispersion coefficients are inconsistent: the axial dispersion coefficient decreases with the rotation speed and increases with the flow rate in the single-phase mode, but increases with rotation speed and decreases slightly with the flow rate in the two-phase mode.     

Electrokinetic diffusioosmotic flow of Ostwald-de Waele fluids near a charged flat plate in the thin double layer limit

Electrokinetic diffusioosmotic flow of Ostwald-de Waele, or power-law, fluids near a large charged flat plate is theoretically investigated for very thin double layers. Solutions to the flow velocity both up-close and far from the flat plate as well as the effective viscosity are presented for general values of the flow behavior index. Results show that given a wall zeta potential, ζ, diffusivity difference parameter, β, and constant imposed solute concentration gradient, both the near and far field diffusioosmotic flow velocities obtained for the respective dilatant and pseudoplastic liquids considerably deviate from those obtained for Newtonian liquids as found in previous literature. This likely suggests that the electrokinetic diffusioosmosis and its complementary effect of diffusiophoresis depend sensitively not only on the ζ-β parametric pair, but also on the possible non-Newtonian characteristics of the electrolytic liquid phase of the system. The theory presented herein can also be readily modified to model or describe electrodiffusioosmosis in power-law fluids, which is likely found in flow situations where the fluid non-Newtonian response, imposed solute concentration gradient, and an additional externally applied electric current density (or electric field) are of equal importance.     

Non-invasive imaging of shallow bubble columns using electrical capacitance tomography

This paper deals with application of non-invasive electrical capacitance tomography to study the hydrodynamics of shallow bed bubble columns. Two bubble columns with different height to diameter ratio were used. Air–kerosene system that represents dielectric two-phase mixture was investigated. The ECT provided good measurement of the gas holdup at different gas velocities compared to the classical pressure measurements. The ECT was able to provide the gas hold up and the bubble velocities distribution across the column diameter at different gas velocities. The study revealed that spatial gas holdup and bubble velocity distributions are sharp with parabolic shape in the small bubble column (H_D/D_C = 5). However, in the large bubble column (H_D/D_C = 4) the gas holdup and bubble velocity profiles were flatter indicating improvement in the mixing homogeneity and leading to well-mixed reactor. 3D graphical visualization of the flow regimes and transition points were also examined using the ECT. In the small bubble column flow regimes were heterogeneous to slugs flow especially at high flow rate, resulted in downward flow near the walls and imperfect mixing.     

A comparison of flow injection methods for sulfide determination based on phenothiazine dyes produced from diverse aromatic amines

In the present work a systematic comparison among spectrophotometric flow injection methods for sulfide determination based on phenothiazine dye production from diverse aromatic p-substituted amines were performed. The behavior of N,N-dimethylphenyl-p-diamine (DMPD), N,N-diethylphenyl-p-diamine (DEPD), phenyl-p-diamine (PPD), p-aminophenol (PAP) and other three aromatic amines was investigated and the chemical parameters of proposed flow methods were optimized by applying central composite design. For each evaluated method the concentration of amine, Fe³⁺ and H₂SO₄ was optimized and after the evaluation of reagents addition order the flow parameters were independently ascertained. Analytical signal was strongly diminished in the presence of iodide for flow methods based on the reaction of sulfide with DMPD, PPD or DEPD while fluoride was considered as an important interference for methods based on the reaction with PPD or PAP. The evaluated aromatic amines have permitted sulfide determination in a wide concentration range from 0.05 to 3.0 mg L^− 1 and limits of detection (3σ) varying from 18.8 to 51.0 μg L^− 1, for DEPD and PPD, respectively. The sensitivity of flow methods based on PPD and DMPD was higher even as PAP has permitted sulfide determination in a large sulfide concentration range. In addition, higher throughput was attained for DMPD method. The proposed methods were applied for sulfide determination in industrial wastewater and the obtained results were in agreement with reference method at 95% confidence level.     

Flow microcalorimeter for heat capacities of solutions

A new type of flow microcalorimeter for measuring heat capacities at constant pressure of liquids and solutions was constructed. This calorimeter is the similar in design to Picker's except for the flow system, which consists of two syringe type of pumps and two flowing paths in each flow cell. It was found that the magnitude of heat loss from cells depended on liquids themselves used and the flow rates of sample liquids. The molar heat capacities, C_p of benzene and ethanol were determined relative to those of cyclohexane and water, respectively. The excess molar heat capacities, C_p(E) for the systems of benzene + cyclohexane and water + ethanol were also determined at 298.15K by the direct mixing method. An inaccuracy for C_p(E) was estimated to be within ± 1%.     

The effect of the solution flow rate on the final mass of metals deposited into a porous electrode at individual and joint deposition. Rear delivery of solution

Pursuing the studies of the effect of solution flow rate and direction on filling of a porous electrode with deposited metals, the peculiarities of individual and joint deposition of metals are studied for the rear solution delivery. In the rear delivery mode, the nonmonotonic dependence of the final mass of the cathodic deposit m _f on the solution flow rate m _v with the maximum at middle flow rates is observed to hold. The main differences from the frontal delivery mode are the much higher mass values in the maximum m _{f, max} (1.5–3.5-fold higher) and the lower concomitant flow rates m _{v, max} (0.05–1 cm³/s). Moreover, the highest mass gains and rate shifts correspond to the lower cathodic polarization values. These differences are associated with the opposite orientation of the polarization and metal-concentration profiles inside the PE, which is typical of the rear delivery, and also with the gradual shift of the PE critical section from the frontal to rear plane as the solution flow rate decreases. For the rear delivery, the m _{f, max} value observed in the direct-flow mode turns out to be even a little higher as compared with the circulation mode. This makes the direct-flow mode of electrolysis in the middle range of flow rates the most efficient condition for the metal codeposition into a PE at the rear delivery. Experimental data on the individual and joint deposition of silver and copper on carbon felt VINN-250 from alkaline thiosulfate solutions at the rear delivery and different solution rates qualitatively agrees with the model calculations for a PE with the same specific surface.     

Microfluidic cells with interdigitated array gold electrodes: Fabrication and electrochemical characterization

Microfluidic flow cells combined with an interdigitated array (IDA) electrode and/or individually driven interdigitated electrodes were fabricated and characterized for application as detectors for flow injection analysis. The gold electrodes were produced by a process involving heat transfer of a toner mask onto the gold surface of a CD-R and etching of the toner-free gold region by short exposure to iodine-iodide solution. The arrays of electrodes with individual area of 0.01 cm² (0.10 cm of length × 0.10 cm of width and separated by gaps of 0.05 or 0.03 cm) were assembled in microfluidic flow cells with 13 or 19 μm channel depth. The electrochemical characterization of the cells was made by voltammetry under stationary conditions and the influence of experimental parameters related to geometry of the channels and electrodes were studied by using K₄Fe(CN)₆ as model system. The obtained results for peaks currents (I_p) are in excellent agreement with the expected ones for a reversible redox system under stationary thin-layer conditions. Two different configurations of the working electrodes, E_i, auxiliary electrode, A, and reference electrode, R, on the chip were examined: E_i/R/A and R/E_i/A, with the first presenting certain uncompensated resistance. This is because the potentiostat actively compensates the iR drop occurring in the electrolyte thin layer between A and R, but not from R to each E_i. This is confirmed by the smaller difference between the cathodic and anodic peak potentials for the second configuration. Evaluation of the microfluidic flow cells combined with (individually driven) interdigitated array electrodes as biamperometric or amperometric detectors for FIA reveals stable and reproducible operation, with peak heights presenting relative standard deviations of less than 2.2%. For electrochemically reversible species, FIA peaks with enhanced current signal were obtained due to redox cycling under flow operation. The versatility of microfluidic flow cells, produced by simple and low-cost technique, associated with the rich information content of electrochemical techniques with arrays of electrodes, opens many future research and application opportunities.     

Electrokinetically driven micro flow cytometers with integrated fiber optics for on-line cell/particle detection

This paper presents an innovative micro flow cytometer which is capable of counting and sorting cells or particles. This compact device employs electrokinetic forces rather than the more conventional hydrodynamic forces technique for flow focusing and sample switching, and incorporates buried optical fibers for the on-line detection of cells or particles. This design approach results in a compact microfluidic system and an easier integration process. The proposed cytometer integrates several critical modules, namely electrokinetic-focusing devices, built-in control electrodes, buried optical fibers for on-line detection, and electrokinetic flow switches for bio-particle collection. A linear relationship exists between the focused stream width (d) and the focusing ratio (F/φ), which is estimated to be D≈134.5−53.8F/φ. The relationship between the particle velocity (U) and the applied voltage (V) is also investigated. Numerical and experimental data confirm the effectiveness of the device when applied to the counting and sorting of 10 μm diameter particles and red blood cells.     

The behaviour of an electrochemical detector used in liquid chromatography and continuous flow voltammetry: Part 1. Mass transport-limited current

A simple expression relating the current at a rectangular channel-type flow-through electrode to the volume flow rate of solution, cell dimensions and physical constants is derived. The expression for steady-state current is valid for laminar flow with neglect of longitudinal depolarizer diffusion. The equation is derived to extract information on the analytical utility of these cells, i.e. signal-to-noise ratio (SNR). For standard amperometric detection the optimum cell design is one in which the width of the cell is equal to the width of the electrode and the length and thickness of the cell are as small as possible, the limit of these dimensions either being physical or dictated by amplifier noise in the output. There is no optimum shape for an electrode of a given size. For standard amperometric detection with a constant cell volume, V, the optimum dimensions are given by b = ($\text{VD}\text{0.42}$U)^{$\text{1}\text{2}$}, (b = thickness, D = diffusion coefficient, -U= average volume flow rate). For flow rate-modulated operation, the optimum thickness is vanishingly small, and the electrode area (shape not critical) is given by A = 0.52 UbD^-1.     

Effect of rate and direction of solution flow on metal deposition in porous electrodes: The final weight and distribution of the deposit

Using an earlier-developed dynamic model for a porous flow-through electrode (PFE) with a high initial conductivity, the effect of the solution’s flow rate (0.05–10 cm/s) and direction on the final metal weight m _f and uniformity of the metal distribution in the porous matrix is studied. It is found that m _f increases with increasing flow rate. However, the dependence is nonmonotonic: it peaks at intermediate flow rates. The peak is most pronounced in the case of rear supply. At high and very low flow rates, m _f is independent of the flow direction. In the first case, the metal distribution profiles almost coincide, while in the second case they are mirror-opposite. The deposit weight correlates well with the index of uniformity of its distribution: all other factors being equal, the more uniform the deposit distribution in PFE, the larger the m _f. These effects are explained by taking into account the joint effect of profiles of cathodic polarization and concentration of metal ions in PFE.     

Hydrophobic polymer monoliths as novel phase separators: Application in continuous liquid–liquid extraction systems

Hydrophobic macroporous polymer monoliths are shown to be interesting materials for the construction of “selective solvent gates”. With the appropriate surface chemistry and porous properties the monoliths can be made permeable only for apolar organic solvents and not for water. Different poly(butyl methacrylate-co-ethylene dimethacrylate) (BMA-EDMA) and poly(styrene-co-divinylbenzene) (PS-DVB) monoliths prepared with tailored chemistries and porosities were evaluated for this purpose. After extensive characterization, the PS-DVB monoliths were selected due to their higher hydrophobicity and their more suitable flow characteristics. BMA-EDMA monoliths are preferred for mid-polarity solvents such as ethyl acetate, for which they provide efficient separation from water. Breakthrough experiments confirmed that the pressures necessary to generate flow of organic solvents through PS-DVB monoliths were substantially lower than for water. A phase separator was constructed using the monoliths as the flow selector. This device was successfully coupled on-line with a chip-based continuous liquid–liquid-extraction (LLE) system with segmented flow. Efficient separation of different solvents was obtained across a wide range of flow rates (0.5–4.0 mL min⁻¹) and aqueous-to-organic flow ratios (β = 1–10). Good robustness and long life-time were also confirmed. The suitability of the device to perform simple, cheap, and reliable phase separation in a continuous LLE system prior to gas-chromatographic analysis was proven for some selected real-life applications.     

An experiment study on fluid heat and mass transfer properties in porous media using MRI

The objective of this study was to understand fluid heat and mass transfer processes in porous media with different pore structures. High-resolution Magnetic Resonance Imaging was used to measure fluid flow velocity and temperature maps in porous media. Firstly, three orthogonal velocity components (V _x , V _y , and V _z ) of single phase flow measurement were evaluated. The flow distribution in porous media is rather heterogeneous, and it is consistent with heterogeneous pore structure, and the velocity in large pore is high. Then we presented initial results from the extension of this work to two-phase flow. The CO₂ channeling phenomena were obvious. And the CO₂ velocity was calculated from saturation of water. Finally, the linearity relationship between temperature and the MRI parameter was determined for porous media, and we measured the temperature distribution of water saturated porous media. The study provides useful data for heat and mass process during CO₂ storage.     

Preparative Isolation of Imperatorin, Oxypeucedanin and Isoimperatorin from a Traditional Chinese Herb Using a HSCCC Strategy Based on Optimization of Rapid Flow Rate

Preparative high-speed counter-current chromatography has been used successfully for the isolation and purification of imperatorin, oxypeucedanin and isoimperatorin from traditional Chinese herb “bai zhi”—Angelica dahurica (Fisch. ex Hoffm) Benth. et Hook using high-speed counter-current chromatography (HSCCC). This was achieved in two stages. The first stage used a high flow HSCCC protocol with a two-phase solvent system composed of n-hexane–ethyl acetate–methanol–water (HEMW) with volume ratios of 5:5:5:5, v/v which isolated isoimperatorin but co-eluted imperatorin and oxypeucedanin. The second stage used HEMW 5:5:4:6, v/v at low flow rate to resolve the co-eluted components from the first stage. The flow rate was optimized by preparative HSCCC. 300 mg of the crude extract was separated, yielding 18.5 mg of imperatorin, 8.3 mg of oxypeucedanin and 9.8 mg of isoimperatorin all at a high purity of over 98%.     

Influence of material transition and interfacial area changes on flow and concentration in electro-osmotic flows

This paper presents a numerical study to investigate the effect of geometrical and material transition on the flow and progression of a sample plug in electrokinetic flows. Three cases were investigated: (a) effect of sudden cross-sectional area change (geometrical transition or mismatch) at the interface, (b) effect of only material transition (i.e. varying ζ-potential), and (c) effect of combined material transition and cross-sectional area change at the interface. The geometric transition was quantified based on the ratio of reduced flow area A₂ at the mismatch plane to the original cross-sectional area A₁. Multiple simulations were performed for varying degrees of area reduction i.e. 0–75% reduction in the available flow area, and the effect of dispersion on the sample plug was quantified by standard metrics. Simulations showed that a 13% combined material and geometrical transition can be tolerated without significant loss of sample resolution. A 6.54% reduction in the flow rates was found between 0% and 75% combined material and geometrical transition.