Use of intermittent jets to enhance flux in crossflow filtration

This paper deals with the influence of a new flow unsteadiness on the permeate fluxes in crossflow filtration. A pneumatically controlled valve generates intermittent jets from the main flow, causing the formation of large vortices moving downstream along the tubular membrane. The main results of the numerical calculation of such flows are given. The experimental study was carried out by filtering a bentonite suspension through an ultrafiltration mineral membrane. Time evolutions of flux were achieved in steady and unsteady operating conditions. Results concerning the influence and limits of the nozzle to tube diameter ratio and the jet velocities are discussed. The applicability of such an unsteady flow is examined with a view to effects on energy consumption and possible viscosity effects.     

Parametric study of the flow and temperature fields in an inductively coupled r.f. plasma torch

A theoretical investigation of the effect of different parameters on the flow and the temperature fields in a radiofrequency inductively coupled plasma is carried out. The parameters studied are: central injection gas flow rate, total gas flow rate, input power, and the type of plasma gas. The results obtained for argon and nitrogen plasmas at atmospheric pressure indicate that the flow and the temperature fields in the coil region, as well as the heat flux to the wall of the plasma confinement tube, are considerably altered by the changes in the torch operating conditions.     

振荡剪切流场下PS/PVME/SiO2复合物的相行为

利用光学显微镜-剪切台联用系统研究了振荡剪切流场下聚苯乙烯（PS）/聚甲基乙烯基醚（PVME）/二氧化硅（SiO₂）纳米粒子复合物的热力学稳定性. 结果表明,小振幅振荡剪切可导致PS/PVME共混物出现类似在稳态流场下的剪切诱导相容及剪切诱导相分离现象. 共混体系存在临界振荡频率ω_c,当振荡频率低于ω_c时,发生剪切诱导相分离（SID）行为,反之发生剪切诱导相容（SIM）行为. SiO₂纳米粒子的加入使复合体系的相容性提高. 存在一个临界SiO₂纳米粒子含量φ_c,当SiO₂纳米粒子含量高于φ_c时,复合体系中不存在临界振荡频率ω_c,低振荡频率下的剪切诱导相分离得到抑制. 此外,复合体系的上述行为与升温速率和共混物组成密切相关.     

The effect of oscillatory flow on crossflow microfiltration of beer in a tubular mineral membrane system – Membrane fouling resistance decrease and energetic considerations

We have investigated the consequences due to the changes in hydrodynamics above the membrane surface brought about by an oscillatory flow in the crossflow microfiltration (CFMF) of beer on a tubular mineral membrane. Experimental results in oscillatory flow filtration were analysed in terms of membrane resistance to filtration and energy consumption and compared with steady flow filtration. Two types of beers were used: a clarified beer composed of colloids and macromolecular material and a rough beer containing in addition yeast cells. Oscillatory flow was found to decrease membrane fouling resistance (up to 100%) in rough beer filtration in the presence of a yeast cell cake layer on the membrane surface, whereas it has no effect in clarified beer filtration in the presence of membrane clogging. The detrimental effect of transmembrane pressure on membrane resistance (at ΔP>1 bar) has been emphasized in both oscillatory and steady flows. The time-average hydraulic power dissipated by friction in the filtration module, in relation with the absolute value of the time-average flow rate in oscillatory flow, was found to be systematically higher than for steady flow filtration. However, the hydraulic energy per unit volume of permeate in the microfiltration of rough beer under oscillatory flow was close to that in steady flow at a time-average tangential velocity of 3 m/s. By considering the specific energy (per m³ of permeate) related to the kinetic energy applied to fluid in oscillatory and steady flow modes, the system by gas compression in oscillatory flow led to a reduction of specific energy ranging from 15% to 40%. Finally the ratio of hydraulic power consumed in oscillatory and steady flow was compared with a theoretical calculation based on the assumption that the oscillating flow regime is quasi-steady.     

Effect of operating variables on the flux and selectivity in sweep gas membrane distillation for dilute aqueous isopropanol

Sweep gas membrane distillation was examined as a possible technique for isopropanol (IPA)–water separation using PTFE hollow fiber membrane module. The composition and flux of the permeate were monitored when feed concentration, operating temperature and flow rate were varied. The upper feed concentration tested was 10 wt.% IPA. Within the feed temperature range of about 20–50°C, IPA selectivity of 10–25 was achieved. Since the concentration near the surface on the membrane increased by the selective adsorption of IPA on the hydrophobic membrane, the selectivity increases. The permeate flux and IPA selectivity increase as feed temperature increase. The flux and selectivity increase at higher flow rates is mainly due to the reduced effects of concentration and temperature polarization. The effect of salt addition to the feed mixture was also examined.     

A new generator of unsteady-state flow regime in tubular membranes as an anti-fouling technique: A hydrodynamic approach

A new generator of pulsatile flow has been developed. It consists of a rotating distributor disc judiciously perforated and placed in front of the entrance plane of a tubular membrane bundle. A laboratory-scale apparatus was built with a five membrane bundle. Two configurations were studied: upstream-disc-position (UDP) and downstream-disc-position (DDP). The main new feature is that the pulsatile flow is generated only in the membranes whereas no variation of flow or pressure occurs elsewhere in the equipment. The hydrodynamic behaviour was successfully modelled; experimental and calculated data are in good agreement. Filtration tests with an aqueous suspension of bentonite showed a close relation between the permeate flux and the pulsatile crossflow velocity. First results are encouraging: a reduction in crossflow velocity of 50% with the same power consumption per unit permeate flux as required for steady crossflow filtration.     

Multicomponent pervaporation process for volatile aroma compounds recovery from pomegranate juice

The present work describes the possibility of using pervaporation process to recover the pomegranate aroma compounds from an actual pomegranate juice and a model aroma solution. Four different chemicals representing four major kinds of aroma compounds, namely, 3-methyl butanal, isopentyl acetate, n-hexanol and α-ionone, were utilized in this work. Three POMS membranes and two PDMS membranes were tested for pervaporation and compared for their separation performance. The influence of various operating parameters such as feed flow rate, feed temperature and permeate pressure on the permeation flux and aroma compounds enrichment factor was investigated. Feed flow rate was shown to have no significant effect on both total flux and aroma enrichment factor, whereas feed temperature and permeate pressure had highly significant effects. An increase in feed temperature led to higher flux and enrichment factor. As permeate pressure increased, the flux and enrichment factor of some aroma compounds decreased. Some of the aroma compounds showed higher enrichment factor at higher permeate pressures. Finally, the activation energy of permeation and the membrane permeability for each aroma compound were determined.     

Fouling in air sparged submerged hollow fiber membranes at sub- and super-critical flux conditions

The overall objective of the present study was to characterize the effect of operating a submerged air sparged membrane system over a wide range of operating conditions (i.e. sub- and super-critical flux conditions) on the extent and mechanisms of membrane fouling during drinking water treatment. The sub- and super-critical flux conditions considered were generated by varying the operating permeate flux, the bulk cross-flow velocity, the flow characteristics (i.e. with or without air sparging) and the configuration of the membrane modules.     

Permeate flow in hexagonal 19-channel inorganic membrane under filtration and backflush operating modes

Numerical simulations and experimental study of incompressible Newtonian permeate flow in porous support of hexagonal 19-channel inorganic membrane are presented both for filtration and backflush operating modes. Under several simplifying assumptions the problem could be treated as two-dimensional potential flow. The mathematical model was solved using finite element method. The results of numerical simulations show that the contributions of particular channels to the total permeate flux are not equal and depend on the ratio of skin layer to porous support permeability as well as on the distance of a channel from the membrane outer surface. For membranes with high permeability of skin layer there is an area of nearly constant pressure around inner channels and their contribution to total flux is negligible. This effect will probably be more pronounced in backflush operating mode while in filtration mode possible dynamic membrane adds a resistance to that of skin layer which leads to more uniform permeate flux distribution. Qualitative trends of the numerical simulations were verified by experiments with ceramic 19-channel membranes of Membralox® type in backflush operating mode.     

Pervaporation performance of crosslinked polyethylene glycol membranes for deep desulfurization of FCC gasoline

An crosslinked polyethylene glycol (PEG) membrane was prepared for fluid catalytic cracking (FCC) gasoline desulfurization. Sulfur enrichment factor come to 4.75 and 3.51 for typical FCC gasoline feed with sulfur content of 238.28 and 1227.24 μg/g, respectively. Pervaporation performance of membranes kept stable within the long time run of 500 h, which indicated that crosslinked PEG membranes had the property of resisting pollution. Judging from chromatographic analysis, the membranes were more efficient for thiophene species. Effects of operation conditions including permeate pressure, feed temperature, feed flow rate and feed sulfur content level on the pervaporation performance were investigated. Permeation flux decreased with increasing permeate pressure while increased with the operating temperature increase. Sulfur enrichment factor increased firstly and decreased then when permeate pressure and temperature rose. The peak value occurred at 10.5 mm Hg and 358 K for model compounds feed (378 K for FCC gasoline feed). Arrhenius relationship existed between flux and operating temperature. Both sulfur enrichment factor and flux were shown to increase with increasing feed flow rate. Permeation flux increased while sulfur enrichment factor decreased as the feed sulfur content increased, but the influence of increasing sulfur content on pervaporation performance weakened when sulfur content come to 600 μg/g.     

Material‐Efficient Microfluidic Platform for Exploratory Studies of Visible‐Light Photoredox Catalysis

We present an automated microfluidic platform for in‐flow studies of visible‐light photoredox catalysis in liquid or gas–liquid reactions at the 15 μL scale. An oscillatory flow strategy enables a flexible residence time while preserving the mixing and heat transfer advantages of flow systems. The adjustable photon flux made possible with the platform is characterized using actinometry. Case studies of oxidative hydroxylation of phenylboronic acids and dimerization of thiophenol demonstrate the capabilities and advantages of the system. Reaction conditions identified through droplet screening translate directly to continuous synthesis with minor platform modifications.     

Comparison of simulated and actual DSC measurements for first-order transitions

A system of differential equations modeling a heat flux DSC is solved and the results are compared with those obtained using a TA Instruments Q1000™ DSC.¹ It incorporates a new heat flow rate measurement technique that determines the heat flow rate between the sample and its pan. Two types of first-order transitions are investigated: melting of a pure substance and solidification of a pure substance including super-cooling. In both transitions, the peak shape obtained using the new heat flow rate measurement and predicted by the model is quite different from that measured using conventional DSC. It is shown that the differences are the result of simplifications implicit in the conventional heat flow rate measurement that is based solely on the difference between sample and reference calorimeter temperatures. Heat flow rates measured using the improved measurement agree very well with the model predictions for heat exchange between the sample and its pan.     

Influence of operating conditions on performance of ceramic membrane used for water treatment

The removal of natural organic matter (NOM) is a critical aspect of potable water treatment because NOM compounds are precursors of harmful disinfection by-products, hence should be removed from water intended for human consumption. Ultrafiltration using ceramic membranes can be a suitable process for removal of natural substances. Previously reported experiments were dedicated to evaluating the suitability of ultrafiltration through ceramic membrane for water treatment with a focus on the separation of natural organic matter. The effects of the membrane operating time and linear flow velocity on transport and separation properties were also examined. The experiments, using a 7-channel 300 kDa MWCO ceramic membrane, were carried out with model solutions and surface water at trans-membrane pressure of 0.2–0.5 MPa. The results revealed that a loose UF ceramic membrane can successfully eliminate natural organic matter from water. The permeability of the membrane was strongly affected by the composition of the feed stream, i.e. the permeate flux decreased with an increase in the NOM concentration. The permeate flux also decreased over the period of the operation, while this parameter did not influence the effectiveness of separation, i.e. the removal of NOM. It was observed that the increased cross-flow velocity resulted in the decrease in the membrane-fouling intensity and slightly improved the retention of contaminants.     

两段式气流床煤气化炉内气固流动数值模拟研究

建立了两段式气流床煤气化炉内气固两相流动的三维计算流体力学（CFD）模型，将气体视为连续介质，在Euler坐标系下考察气相的运动；将颗粒视为离散体系，在Lagrange坐标系下研究颗粒的运动。利用所建CFD模型对基本设计尺寸和操作条件下的两段式气流床煤气化炉内气固两相流动进行了模拟，给出了两段式气流床煤气化炉内的气固两相流动的规律和颗粒的分布规律。在此基础上，针对不同的结构(喉口直径变化)和不同的操作条件（两段气固进料量变化）进行了一系列的模拟比较。结果表明，喉口直径的变化对于炉内气固两相流动及颗粒分布有重要影响。随着喉口直径减小，喉口附近区域的气相回流增强，颗粒运动轨线变得更加曲折，颗粒分布发生明显变化。两段气固流量的改变可以明显改变炉内气固流动，随着一段反应区的气固流量增加和二段反应区气固流量减小，一段反应区内的气相回流更加显著， 二段反应区气相回流减弱，颗粒螺旋上升运动增强，反应器边壁处颗粒浓度增大，颗粒沉积现象减弱。     

Improved mesenchymal stem cell seeding on RGD-modified poly(L-lactic acid) scaffolds using flow perfusion

Arg-Gly-Asp (RGD) has been widely utilized to increase cell adhesion to three-dimensional scaffolds for tissue engineering. However, cell seeding on these scaffolds has only been carried out statically, which yields low cell seeding efficiencies. We have characterized, for the first time, the seeding of rat mesenchymal stem cells on RGD-modified poly(L-lactic acid) (PLLA) foams using oscillatory flow perfusion. The incorporation of RGD on the PLLA foams improves scaffold cellularity in a dose-dependent manner under oscillatory flow perfusion seeding. When compared to static seeding, oscillatory flow perfusion is the most efficient seeding technique. Cell detachment studies show that cell adhesion is dependent on the applied flow rate, and that cell attachment is strengthened at higher levels of RGD modification.     

Economic aspects of critical flux operability in star shaped microfiltration membranes: Influence of some operating conditions

The economic feasibility of operating at the achievable critical flux under different operating parameters (feed concentration, crossflow velocities and pH) using non-circular channelled membranes has been investigated. The increase in critical fluxes with increasing crossflow velocities is accompanied by increasing axial pressure loss. This leads to substantial increase in the specific energy consumption, reducing the energy-saving potential. Minimum specific energy consumption occurs at the crossflow velocity of 0.9 m s⁻¹ where the trade-off between axial pressure loss and the achievable critical flux occurs. Increasing the feed concentrations and pH led to declining and increasing critical fluxes, respectively. Axial pressure loss remains consistent at feed concentrations <10 g l⁻¹ and increases at feed concentrations >10 g l⁻¹. This is attributed to the change in the viscosity of the suspension which affects the specific energy consumption. The influence of pH on critical flux is attributed to the changes in the titanium dioxide particle charges and coincides with the changes in the viscosity of the suspension. The optimum energy-saving potential was found at pH 9.0. Solution chemistry (particle charges and rheology) and hydrodynamics influence the achievable critical flux and axial pressure loss within these channels which ultimately determine the economics of operation.     

Effect of the Mixture Composition on Shear and Extensional Rheology of Recycled PET and ABS Nanocomposites

Summary: Recycled PET as well as ABS - organomodified montmorillonite nanocomposites were prepared via melt compounding in a counter-rotating twin screw extruder. The topological changes in polymer matrices as dependency on clay modification have been evaluated from dynamic experiments in the shear flow using low amplitude oscillatory measurements. Flow characteristics of all studied organoclay nanocomposites showed shear-thinning behavior at low frequencies. Filling of PET with some organoclays led to degradation reactions, which were reflected by lower magnitudes of viscosity and storage modulus in the range of higher frequencies as compared to unfilled polymer matrix. On the contrary, no degradation during the processing of different organoclays with recycled ABS has been observed.     

R12 hydrate formation kinetics based on laser light scattering technique

Gas hydrates are non-stoichiometric crystalline compounds of water with gas at a certain temperature and pressure. Compared to the thermodynamics of hydrate formation, our knowledge on the kinetics aspect is rather immature. It is well known that the kinetics of hydrate formation/dissociation plays an important role in many industrial cases, such as the exploitation of methane hydrate underground, the storage and transportation of natural gas in solid hydrate state, the inhibition of hydrate i…     

Generalized integral and similarity solutions of the concentration profiles for osmotic pressure controlled ultrafiltration

A mathematical model describing the concentration polarization phenomenon during osmotic pressure controlled ultrafiltration is presented. Generalized integral and similarity solutions of the concentration profile in the mass transfer boundary layer are obtained. The parameters governing the shape of the concentration profile vary with time in case of a batch cell and axial distance in a cross flow cell. The model is used to predict the permeate flux and the solute rejection simultaneously during unstirred batch cell and cross flow UF. The results obtained by integral and similarity solutions are compared with the results of detailed numerical solution of the governing equations for both the systems. The predictions of permeate flux from the generalized integral method are also compared with some approximate solutions in order to assess the limitations of the various approximations. UF experiments were performed with Dextran (T-20) in cross flow system and with PEG-6000 and Dextran (T-40 and T-20) in unstirred batch cell. Predictions of the model are in remarkably good agreement with detailed simulation as well as experimental results. Moreover, the integral solution can also account for the variation of diffusivity with solute concentration. Comparisons show that (a) while the generalized integral method is much simpler than the detailed numerical solutions, it is much more general and accurate than other analytical and semi-analytical solutions, and, (b) the proposed solution predicts the osmotic pressure controlled flux decline accurately over a wide range of operating conditions. The expression for gel layer governed UF (constant membrane surface concentration) is found to be an asymptotic case of the present solution.     

A new instrument for measuring the viscoelastic properties of dilute polymer solutions

A new oscillating capillary viscometer has been developed and used for measuring viscoelastic flow properties of dilute polymer solutions. These flow properties are determined from measurements of the pressure to volume flow relationships for sinusoidal flow in cylindrical glass capillaries. The theory for this measurement procedure is based upon the known theory for oscillatory flow of a viscoelastic fluid in circular tubes and which is presented with a few supplementations in this paper.The oscillatory flow is generated by a piezoelectric driver which is dipped directly into the aqueous solution. The advantage of this driver is that the excitation voltage for the piston is a direct measure of the motion of the piston. Changes in pressure are measured with a sensitive low-pressure quartz tranducer.The viscometer was tested with aqueous glycerol solutions and a gelatin gel. The viscoelastic flow properties of dilute polymer solutions (gelatin, gelatin/color-coupler, polyacrylamide) were then investigated in the frequency range 5 Hz to 150 Hz at very small volume flow amplitudes. The results presented illustrate the suitability of the method. The results are also evaluated with regard to the stabilizing action of slightly viscoelastic gelatinous coating liquids in the high-speed coating process in the manufacture of photographic materials.