Nature of flow on sweeping gas membrane distillation

The process of sweeping gas membrane distillation (SGMD), with the liquid feed and the sweeping gas counterflowing in a plate and frame membrane module, has been studied. A theoretical model, which was presented in a previous paper and permitted to obtain the temperature profiles inside the fluid phases, has been developed in order to analyse the physical nature of the transmembrane water flux. Two porous hydrophobic membranes have been studied in different experimental conditions. The influence of some relevant parameters, such as the inlet and outlet temperatures or the circulation velocities of the fluids, has been studied. The experimental results have been analysed according to the model and the conclusion is that the water transport takes place, apparently, via a combined Knudsen and molecular diffusive flow mechanism. From the temperature profiles, a local temperature polarisation coefficient may be defined. From this local value, an overall one for the whole system is then defined. The new theoretical predictions have been applied to the obtained results and the accordance may be considered good.     

Automation of an experimental system for the microbial epoxidation of propene and 1-butene

An experimental set-up for automatic gas chromatographic analysis of circulation gas in a batch-reactor system is described. Gas sampling, substrate addition, data acquisition and data reduction are done with a coupled programmable integrator and microcomputer. On-line monitoring of the microbial oxidation of the gaseous alkenes, propene and 1- butene, to the corresponding epoxides is used to illustrate the operation of the experimental system. Measured gas concentrations of alkene and alkene oxide can be converted readily to quantify the reaction course in the liquid phase(s) of the circulation system. Results are presented for both one liquid phase (water) and two liquid phases (water and organic solvent) present in the reactor. The operational stability of the immobilized-cell system used for the epoxidations can be assessed by computer-controlled addition of gaseous alkene.     

Critical parameters in a supported liquid membrane extraction technique for ionizable organic compounds with a stagnant acceptor phase

The reviews cover important critical parameters that are often optimized in a supported liquid membrane extraction technique in both flat sheet and hollow fibre designs for ionizable organic molecules. Understanding of these parameters can enable one to predict the behavior of the compound before hand and thus reduce the number of optimization experiments. Moreover, less number of experiments can be also generated using statistical techniques which are now becoming more commonly used. Supported liquid membrane extraction optimal parameters such as the conditions of the pH of the acceptor and donor phases should easily be fixed from the pKa values of the compounds. Other parameters, including the polarity of the compound can help to predict the partitioning into the membrane and the behavior of the compound. The influence of parameters such as temperature on the mass transfer in supported liquid membrane depends on the design of the module, experimental design and type of mass transfer controlling the extraction process.     

Rapid purification of cell encapsulated hydrogel beads from oil phase to aqueous phase in a microfluidic device

In this paper, we demonstrate a new type of microfluidic chip that can realize continuous-flow purification of hydrogel beads from a carrier oil into aqueous solution by using a laminar-like oil/water interface. The microfluidic chip is composed by two functional components: (1) a flow-focusing bead generation module that can control size and shape of beads, (2) a bead extraction module capable of purifying hydrogel beads from oil into aqueous solution. This module is featured with large branch channels on one side and small ones on the opposite side. Water is continuously infused into the bead extraction module through the large branch channels, resulting in a laminar-like oil/water interface between the branch junctions. Simulation and experimental data show that the efficiency of oil depletion is determined by the relative flow rates between infused water and carrier oil. By using such a microfluidic device, viable cells (HCT116, colon cancer cell line) can be encapsulated in the hydrogel beads and purified into a cell culture media. Significantly improved cell viability was achieved compared to that observed by conventional bead purification approaches. This facile microfluidic chip could be a promising candidate for sample treatment in lab-on-a-chip applications.     

Amination of Cyclohexane by Dielectric Barrier Discharge Processing in a Continuous Flow Microreactor: Experimental and Simulation Studies

A miniaturized flow device has been developed to combine microfluidics technology and plasma process. In this microreactor, atmospheric pressure dielectric barrier discharges are generated in a gas in contact with a liquid phase. This study was conducted with plasma generated in ammonia in contact with a flow of liquid cyclohexane. Cyclohexylamine was synthesized with a good selectivity, and the process can be implemented to improve conversion and effectiveness. Numerical simulations confirmed that NH₂ radicals are generated in the plasma and react with cyclohexyls radicals to achieve the reaction, giving a selectivity of 50% and a total molar conversion of 20% of cyclohexane. The effects of voltage and frequency on the selectivity and the experimental conversion rate were studied and discussed.

     

Synthesis of Functional Oxide Nanoparticles Through RF Thermal Plasma Processing

A method of synthesizing functional nanostructured powders through reactive thermal plasma processing has been developed. Nano-sized oxide powders, including titanium dioxide and some functional oxides, were synthesized by the oxidation of liquid precursors. Oxides with the prescribed cation ratio of the liquid precursor can be synthesized with this technique, and it is possible to precisely adjust the chemical composition, which is linked to the appropriate functions of ceramic materials. Quench gases, either injected from the shoulder of the reactor or injected counter to the plasma plume from the bottom of the reactor, were used to vary the quench rate; therefore, the particle size of the resultant powders. The experimental results are well supported by numerical analysis on the effects of quench gases on the flow pattern and temperature field of thermal plasma as well as on the trajectory and temperature history of particles. Plasma-synthesized TiO₂ nanoparticles showed phase preferences different from those synthesized by conventional wet-chemical processes. Nano-sized particles of high crystallinity and nonequilibrium chemical composition were formed in one step via reactive thermal plasma processing. The plasma-synthesized nanoparticles were spherical and hardly agglomerated, and high dispersion properties were observed, i.e., the plasma-synthesized TiO₂ nanoparticles were individually dispersed in water.     

Dehumidification and humidification of air by surface-soaked liquid membrane module with triethylene glycol

A novel liquid membrane system, a surface-soaked liquid membrane, with triethylene glycol (TEG) on the hydrophilic-treated surface of the hydrophobic microporous membrane was developed and used for the dehumidification and humidification of air. The selectivity of the TEG liquid membrane for water vapor with respect to air was over 2000, which was derived from the selective absorption of the TEG liquid. A flat-type liquid membrane module with a dual membrane surface was designed, of which the TEG liquid membrane thickness was 18 μm and the permeation area was 0.13 m². The liquid membrane humidifier and dehumidifier consisted of the membrane module and a vacuum pump. As a dehumidifier, the membrane system recovered water vapor at 4.1 g/h from 70%RH room air at 298 K. For use as a humidifier, the air flow was effectively humidified by the permeated water vapor through the membrane module. The effects of the air humidity and sweep air flow rate were studied and discussed. Simple model calculations based on the permeability of the water vapor well predicted the experimental results.     

A Three-Dimensional Two-Phase Model for Thermal Plasma Chemical Vapor Deposition with Liquid Feedstock Injection

In this paper, a comprehensive model for thermal plasma chemical vapor deposition (TPCVD) with liquid feedstock injection is documented. The gas flow is assumed to be steady, of a single temperature. Radiation and charged species contributions are excluded, but extensive homogeneous and heterogeneous chemistry is included. The liquid phase is traced by considering individual droplets. Discussion on the model's application to diamond production from acetone in a hydrogen–argon plasma is included. The major conclusions are: (1) Liquid injection possesses a capability to deliver the hydrocarbon precursor directly onto the deposition target. (2) For the case of complete evaporation of the droplet before reaching the substrate, the deposition rate is similar to that obtained with gaseous precursors. (3) The computational results compare well with experimental data. The modeling results can be used to optimize the injection parameters with regard to the deposition rate.     

Microfiltration platform for continuous blood plasma protein extraction from whole blood during cardiac surgery

This report describes the design, fabrication, and testing of a cross-flow filtration microdevice, for the continuous extraction of blood plasma from a circulating whole blood sample in a clinically relevant environment to assist in continuous monitoring of a patient's inflammatory response during cardiac surgeries involving cardiopulmonary bypass (CPB) procedures (about 400,000 adult and 20,000 pediatric patients in the United States per year). The microfiltration system consists of a two-compartment mass exchanger with two aligned sets of PDMS microchannels, separated by a porous polycarbonate (PCTE) membrane. Using this microdevice, blood plasma has been continuously separated from blood cells in a real-time manner with no evidence of bio-fouling or cell lysis. The technology is designed to continuously extract plasma containing diagnostic plasma proteins such as complements and cytokines using a significantly smaller blood volume as compared to traditional blood collection techniques. The microfiltration device has been tested using a simulated CPB circulation loop primed with donor human blood, in a manner identical to a clinical surgical setup, to collect plasma fractions in order to study the effects of CPB system components and circulation on immune activation during extracorporeal circulatory support. The microdevice, with 200 nm membrane pore size, was connected to a simulated CPB circuit, and was able to continuously extract ~15% pure plasma volume (100% cell-free) with high sampling frequencies which could be analyzed directly following collection with no need to further centrifuge or modify the fraction. Less than 2.5 ml total plasma volume was collected over a 4 h sampling period (less than one Vacutainer blood collection tube volume). The results tracked cytokine concentrations collected from both the reservoir and filtrate samples which were comparable to those from direct blood draws, indicating very high protein recovery of the microdevice. Additionally, the cytokine concentration increased significantly compared to baseline values over the circulation time for all cytokines analyzed. The high plasma protein recovery (over 80%), no indication of hemolysis and low level of biofouling on the membrane surface during the experimental period (over 4 h) were all indications of effective and reliable device performance for future clinical applications. The simple and robust design and operation of these devices allow operation over a wide range of experimental flow conditions and blood hematocrit levels to allow surgeons and clinicians autonomous usage in a clinical environment to better understand the mechanisms of injury resulting from cardiac surgery, and allow early interventions in patients with excessive postoperative complications to improve surgical outcomes. Ultimately, monolithic integration of this microfiltration device with a continuous microimmunoassay would create an integrated microanalysis system for tracking inflammation biomarkers concentrations in patients for point-of-care diagnostics, reducing blood analysis times, costs and volume of blood samples required for repeated assays.     

Mass and momentum transport in extra-luminal flow (ELF) membrane devices for blood oxygenation

In this paper, we report on the characterisation of transport in membrane modules for blood oxygenation where blood is circulated outside hollow fibre membranes arranged in double layer cross-laid mats at an angle with respect to the main direction of blood flow. The effect of design and operating variables on module performance was investigated with respect to oxygen transfer into water, as gaseous oxygen and water are circulated counter-currently, respectively inside the membrane lumen and through the membrane assembly.Increasing water flow rates and membrane angles enhanced oxygen transfer across the membrane and resulted in robust operation but also in high pressure drops.Module pressure drop and oxygen transfer rate were correlated to module geometry, fibre packing density, water flow rate and membrane angle with respect to the main direction of the liquid flow in non-dimensional equations that can be used by membrane module manufacturers for the design of optimal ELF blood oxygenators. The results suggest that an optimum membrane angle exists, beyond which module operation is not convenient in terms of energy.     

现代煤气化技术的开发与进展

评述了现代煤气化技术开发现状，对加压固定床气化，流化床气化，水煤浆气流床气化和干粉气流床气化典型代表技术的发展进行分析。结合热力学和动力学分析提出了未来煤气化技术发展的原则。鉴于目前制氧成本仍然是制约煤气化技术发展的最大因素，认为一方面应加速高效廉价的大规模制氧技术的开发，另一方面要注重氧耗低的气化技术的开发，重视过程集成概念和技术经济的优化。理论分析和已有研究表明粉煤/块煤双粒级进料液态排渣固定床气化、两段（多段）进料干粉气流床气化、流化床部分气化与气流床气化或CFB燃烧集成技术具有各自特点和良好的发展前景。     

Measurement of adsorption of a single component from the liquid phase: modelling investigation and sensitivity analysis

In this work, we consider an alternative approach for the measurement of adsorption from the liquid phase. Consider a mixture consisting of a non-adsorbed component (B) and an adsorbed component (A) present at some low concentration. Initially, a feed of component B only flows through a column packed with an adsorbent. Then, the feed is switched to the mixture of A and B. As soon as the mixture enters the column, there will be a reduction in the outlet flow rate as component A leaves the liquid phase and passes into the adsorbed phase. There are three stages to this work. The first is to develop overall and component balances to show how the amount adsorbed of component A can be determined from the variation in the column outlet flow rate. The second is to determine the actual variation in the column outlet flow rate for both plug flow and axial-dispersed plug flow. The final stage is to consider the suitability of a gravity-fed system to deliver the feed to the column. An analysis of the results shows that the experimental arrangement should be able to accurately monitor adsorption from the liquid phase where the mass fraction of the solute is of the order of 1%: the limiting experimental factor is how constant the volumetric flow rate of the liquid feed can be maintained.     

Temporal evolution of the3H levels in the surface waters around the Almaraz Nuclear Power Plant

We have quantified the evolution during 1994 of the impact on the Tagus river of liquid releases of³H (51.3 TBq in the cited year), originating from the functioning of the Almaraz Nuclear Power Plant, and conditioned by the management of the cooling reservoir water. Taking into account, on the one hand, that tritiated water is hydrodynamically indistinguishable from untritiated water when both form part of the same mass of liquid, and, on the other, the practically null stratification and forced circulation of the water in the cited cooling reservoir, together with the hydrological fluxes interchanged between the said reservoir and the Tagus river (which is entirely regulated in the section under study and, because of prolonged drought, had a relatively small flow during the study period), we were able to model satisfactorily the temporal evolution of the³H activity in the cooling reservoir.     

Design, simulation and application of a new micromixing device for time resolved infrared spectroscopy of chemical reactions in solution

We present a novel micromachined fast diffusion based mixing unit for the study of rapid chemical reactions in solution with stopped-flow time resolved Fourier transform infrared spectroscopy (TR-FTIR). The presented approach is based on a chip for achieving lamination of two liquid sheets of 10 microm thickness and approximately 1 mm width on top of each other and operation in the stopped-flow mode. The microstructure is made on infrared transmitting calcium fluoride discs and built up with two epoxy negative photoresist layers and one silver layer in between. Due to the highly laminar flow conditions and the short residence time in the mixer there is hardly any mixing when the two liquid streamlines pass through the mixing unit, which allows one to record a mid-IR transmission spectrum of the analytes prior to reaction. When the flow is stopped, the reactant streams are arrested in the flow-cell and rapidly mixed by diffusion due to the reduced interstream distances and the reaction can be directly followed with hardly any dead time. On the basis of two model reactions-neutralisation of acetic acid with sodium hydroxide as well as saponification of methyl monochloroacetate-the performance of the mixing device was tested revealing proper functioning of the device with a time for complete mixing of less than 100 ms. The experimental results were supported by numerical simulations using computational fluid dynamics (CFD), which allowed a reliable, quantitative analysis of concentration, pressure and flow profiles in the course of the mixing process.     

Novel electroosmotic micromixer configuration based on ion-selective microsphere

In this paper, a micromixer of a new configuration is presented, consisting of a spherical chamber in the center of which an ion-selective microsphere is placed. Stratified liquid is introduced through the chamber via inlet and outlet holes under an external pressure gradient and an external electric field is directed in such a way that the resulting electroosmotic flow is directed against the pressure-driven flow, resulting in mixing. The investigation is carried out by direct numerical simulation on a super-computer. Optimal values of the applied electric field are determined to yield strong mixing. Above this optimal mixing regime, a number of instabilities and bifurcations are realized, which qualitatively coincide with those occurring during electrophoresis of an ion-selective microgranule. As shown by our calculation, these instabilities do not lead to an enhanced mixing. The resulting electroconvective vortices remain confined near the surface of the microgranule, and do not sufficiently perturb the stratified fluid flow further from the granule. On the other hand, another type of instability caused by the salt concentration gradient can generate sufficiently strong oscillations to enhance mixing. However, this only occurs when the external electric field is sufficiently high that the electroosmotic flow is comparable to the pressure-driven flow. This ultimately leads to creation of reverse flows of the liquid and cessation of the device operation. Thus, it was shown that the best mixing occurs in the absence of electrokinetic instability. Based on the data obtained, it is possible to select the necessary geometric characteristics of the micromixer to achieve the optimal mixing mode for a given set of liquids, which may be ten times more effective than passive mixers at the same flow rates. A comparison with the experimental data of the other authors confirms the effectiveness of this device and its other capabilities. Furthermore, the basic device design can be operated in other modes, for example, an electrohydrodynamic pump, a streaming current generator, or even a micro-reactor, depending on the system parameters and choice of an ion-selective granule.     

Automated Extraction of Drugs from Biological Fluids

Abstract

An automated continuous flow liquid-liquid extraction procedure is described for the separation of the H₂-antagonist loxtidine from plasma samples containing two metabolites which interfere in the radioimmunoassay of the drug. The extraction of the bronchodilator salbutamol was studied using the DuPont Prep I automated liquid solid extraction apparatus, with a 12 cartridge capacity, and a vacuum extraction box designed in this laboratory to hold 30 Sep-pak C-18 (Waters Associates) cartridges. Twenty-four plasma samples per hour can be automatically processed with the Prep I. Although the vacuum box is not fully automated 45 plasma samples per hour can be processed. The Prep I can only be used with DuPont XAD, strong cation and anion exchange cartridges. Cartridges containing alumina, silica, floril, cation and anion exchange resins and reverse phase packings can all be used with the vacuum extraction box. The latter costs only a fraction of the Prep I and therefore each analyst can have his own unit.     

Flow birefringence of concentrated polymer solutions in two-dimensional flows

The results of flow birefringence measurements are reported for polymer solutions of moderate concentration subjected to a wide range of two-dimensional flows. These flows were generated in a four-roll mill which enables one to systematically vary the ratio of the vorticity to the rate of strain in the flow while holding the velocity gradient constant. It is shown that steady-state birefringence data collected over a wide range of flow types can be correlated against the eigenvalue of the velocity gradient tensor, in agreement with criterion for strong and weak flows from model calculations. Transient birefringence measurements in which purely extensional flows were started from rest are also reported. It was observed that the birefringence went through a pronounced overshoot in time for two different polymer/solvent systems. Flow induced increases in the solution turbidity were also observed and the increased turbidity remained constant over a period of many hours after extensional flows were arrested. The birefringence, on the other hand, decayed to zero almost immediately after the flows were stopped. These changes in the turbidity suggest that crystallization of the polymer was occurring. The qualitative results of experiments are compared to recent network model calculations using the theory of Yamamoto for concentrated polymer systems. It is found that this model can predict qualitatively many of the experimental observations if the function describing the breakage of polymer chain entanglements is allowed to depend on the conformation of the polymer segments bridging the entanglements. In particular, this dependency of the entanglement breakage on the conformation of the network segments leads to a predicted overshoot of birefringence when purely extensional flows are started from rest. It is also demonstrated through this model that birefringence data taken over a wide range of flow types can be used to estimate the degree to which the network deforms affinely with the flow field.     

Surface tension drawing of liquid from microplate capillary wells

Pressure differentials are routinely used to actuate flow in capillaries. We advance here an alternative means of flow generation that capitalizes on the extension of a liquid bridge achieved by the drawing of a rod through the action of surface tension. This meets the exigencies of creating controllable flow using simpler and more compact means. We found the ability to generate controllable flow to be strongly affected by the liquid bridge sustaining features, and that the use of rod diameters larger than the capillary was more conducive. The extensional flow resulting from the rupture of the liquid bridge was also found to have a strong circulation component which facilitated mixing. The approach here is highly amenable for use in capillary well microplates which have significant advantages over standard microplates. The features of this approach offer usage possibilities in biochemical applications in the field, such as in the leukocyte cell adhesion and hemagglutination tests of blood samples.     

Interfacial organic synthesis in a simple droplet-based microfluidic system

A spherical liquid-liquid interface can be obtained by dispersing one liquid phase into another to form droplets, which will facilitate the two-phase reactions between the immiscible participating fluids. The phase transfer catalysts assembled at the droplet "wall" catalyze the reactions between the aqueous and organic phases. The study illustrates an interfacial synthetic approach which is ideal for the biphasic reaction by taking advantage of the droplet-based microdevice. The improved reaction efficiency can be attributed to the high surface-to-volume ratio and internal flow circulation in the droplets.     

Molecular dynamics simulation of planar elongational flow at constant pressure and constant temperature

Molecular dynamics simulations of liquid systems under planar elongational flow have mainly been performed in the NVT ensemble. However, in most material processing techniques and common experimental settings, at least one surface of the fluid is kept in contact with the atmosphere, thus maintaining the sample in the NpT ensemble. For this reason, an implementation of the Nose-Hoover integral-feedback mechanism for constant pressure is presented, implemented via the SLLOD algorithm for elongational flow. The authors test their procedure for an atomic liquid and compare the viscosity obtained with that in the NVT ensemble. The scheme is easy to implement, self-starting and reliable, and can be a useful tool for the simulation of more complex liquid systems, such as polymer melts and solutions.