Influence Of Cross-flow Velocity Research Articles

Behavior of bubble plume in shear-thinning crossflowing liquids

The behavior of bubble plume in crossflows was investigated by experimental and theoretical methods. The high-speed photography method was applied to analyze the visualization of bubble plume in tap water and carboxyl methyl cellulose (CMC) aqueous solution. The influence of crossflow velocity, superficial gas velocity and rheology of liquid phase on the inclination trajectory of bubble plume was studied. The results indicated that the trajectories of bubble plumes in tap water and CMC aqueous solutions approximated linearly, while the inclination characteristic of the bubble plume in CMC aqueous solutions were significantly different from those in tap water due to the effect of the rheological properties. The inclination angle of bubble plume in CMC aqueous solution was one-third more than that in tap water at high crossflow velocity. A correlation was developed via dimensional analysis to predict the inclination trajectories of bubble plumes in Newtonian and shear-thinning non-Newtonian fluid system. Considering the non-Newtonian rheology, the modified integral model of bubble plume was applied for theoretical calculation of centroids of bubble plume in crossflow.

Influence of Reynolds number synthetic jet dynamic in crossflow configuration on heat transfer enhancement

The influence of synthetic jets on heat transfer rate along a flat plate has been studied for laminar and turbulence cross-flow and at several exciting frequencies (0 < f < 12.8 Hz). To better understand such interactions, both cross-flow field without and with synthetic jets in a quiescent environment were preliminarily reviewed. The influence of their confrontation on flow structure was studied, particularly for a frequency of 12.8 Hz and the roles of this frequency as well as four others on heat transfer coefficient were determined. Lastly, the influence of cross-flow velocity with its fluctuating activity on synthetic jet development was closely observed.

Modelling of optimal back-shock frequency in hollow-fibre ultrafiltration membranes II: Semi-analytical mathematical model

The influence of cross-flow velocity and transmembrane pressure on the optimal back-shock frequency and normalized net flux during back-shocking has been studied using a semi-analytical mathematical model. The model uses the flux as a function of time without back-shocking together with knowledge of the streamlines and pathlines during the back-shock cycle to predict the optimal normalized net flux as a function of forward filtration time.The model was used to investigate three different transmembrane pressures and three different cross-flow velocities during a back-shock cycle. The net flux was found to increase under all operating conditions when using back-shocking. The greatest increase in normalized net flux was found at the highest cross-flow velocity and the highest transmembrane pressure, and corresponds to an increase of 37% compared to the steady-state flux. The highest cross-flow velocity and the highest transmembrane pressure gave the highest optimal back-shock frequency of 0.21Hz. The optimal back-shock frequency was found to decrease with increasing pressure and decreasing cross-flow velocity.The model is easy to use in different applications as it is easy to measure flux during forward filtration without back-shocking. Good agreement was found between the semi-analytical model and a model based on computer fluid dynamics in predicting both the value of the optimal normalized net flux and the optimal back-shock frequency.

Nanofiltration and reverse osmosis surface topographical heterogeneities: Do they matter for initial bacterial adhesion?

The role of the physicochemical and surface properties of NF/RO membranes influencing bacterial adhesion has been widely studied. However, there exists a poor understanding of the potential role membrane topographical heterogeneities can have on bacterial adhesion. Heterogeneities on material surfaces have been shown to influence bacterial adhesion and biofilm development. The purpose of this study was therefore to investigate whether the presence of membrane topographical heterogeneities had a significant role during bacterial adhesion as this could significantly impact on how biofouling develops on membranes during NF/RO operation. An extensive study was devised in which surface topographical heterogeneities from two commercial membranes, NF270 and BW30, were assessed for their role in the adhesion of two model organisms of different geometrical shapes, Pseudomonas fluorescens and Staphylococcus epidermidis. The influence of cross-flow velocity and permeate flux was also tested, as well as the angle to which bacteria adhered was compared to the flow direction. Bacterial adhesion onto the membranes and in their surface topographical heterogeneities was assessed using Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), fluorescence microscopy and image analysis. Results showed that up to 30% of total adhered cells were found in membrane defect areas when defect areas only covered up to 13% of the membrane surface area. This suggests that topographical heterogeneities may play a significant role in establishing environmental niches during the early stages of biofilm development. Furthermore, no noticeable difference between the angle of cell attachment in defect areas compared to the rest of the membrane surface was found.

Flow dynamics of multi-lateral jets injection into a round pipe flow

Controlling the mixing field of turbulent jets is an important approach in optimizing practical combustion systems. The use of multi-lateral jets upstream from the nozzle exit to control mixing fields is one particular method. Existing studies have investigated jets into a confined cross-flow (JICCF) for dilution mixing, but there is a paucity of data available on the fundamentals for turbulent mixing capabilities of JICCF. The current study investigates the flow structures and Primary Reynolds number mixing characteristics within a round pipe flow modified by four equi-spaced, lateral side injectors. Experiments are conducted in a primary water jet flow that is modified with smaller jets located one central (axial) jet diameter upstream of the nozzle exit. Flow structures and mixing within the nozzle are non-intrusively characterized using simultaneous planar optical techniques. Planar laser-induced fluorescence is used to measure the scalar mixing of the side and axial jet streams, and particle imaging velocimetry is used to measure the planar velocities. Several cases are investigated with variable primary flow to explore the influence of cross-flow velocity on the induced mixing structures within the nozzle. By varying the momentum ratio, three characteristic flow modes are identified within the primary flow, namely streaming mode, impinging mode, and backflow mode. The impact of these modes on the flow and scalar fields is presented and discussed.

OPTIMIZING THE NANOFILTRATION OPERATING CONDITIONS AS POST TREATMENT STEP IN THE GROUNDWATER DENITRIFICATION PROCESS

Two types of nanofiltration membranes had been used to study the influence of cross flow velocity on the membrane filtration of denitrification effluent (NF270 and NF90). Filtration had been conducted at constant transmembrane pressure of 5 bar and variable cross flow velocity (0.03, 0.06, 0.15 and 0.39 ms -1 ). The obtained normal flux was 0.47, 0.58, 0.59 and 0.77for NF270 membranes and 0.35, 0.38, 0.41 and 0.39 for NF90 membranes, the increase in cross flow velocity had enhanced flux performance of NF270 membranes more than NF90. The structure of the accumulated particles on the membrane surface had changed with each increment in the cross flow velocity, the accumulated particle count had decreased on the following percentages 35.65, 43.54 and 56.62% for NF270 and 34.85, 40.10 and 46.71% for NF90 membranes. The achieved active biomass concentrations was 4.65E+07, 1.96E+07, 1.70E+07 and 1.29E+07 ng.m -3 on the NF270 membranes and 7.78E+07, 4.41E+07, 3.74E+07 and 3.54E+07 on NF90. The cross flow velocity higher than 0.06 ms -1 had minor influence on the bioparticles removal

Assessing the major factors affecting the performances of forward osmosis and its implications on the desalination process

This study evaluates the influence of some of the major factors affecting the performances of forward osmosis (FO) desalination and assessed their potential implications on the overall process. The major factors assessed include membrane properties, draw solution (DS) properties, feed solution (FS) properties and the operating conditions. The influence of the membrane properties was evaluated using three types of membranes and in doing so we have also introduced one newly synthesized proprietary thin film composite FO (TFC-FO) membrane. The performances of TFC-FO membrane in terms of water flux and reverse solute flux were significantly higher than the commercial cellulose triacetate FO membrane and TFC reverse osmosis membrane in FO process. Although adequate osmotic pressure of DS is desirable for FO process, the influence of DS osmotic pressure was less significant at higher DS osmotic pressure and therefore selecting an optimum initial osmotic pressure is essential for FO process to minimize pumping energy. A critical DS concentration has been hypothesized to minimize the implications of DS concentrations on the capital and operational cost of the FO desalination plant. Total dissolved solids (TDS) of the FS play a significant role in the performance of FO process however the influence of feed TDS was less significant for feed higher than 20,000mg/L indicating that FO has a promising potential for use with high TDS feed water. Although, water flux decreased, the reverse solute flux (RSF) and specific RSF also decreased slightly at higher feed TDS. For operating parameters, the influence of crossflow velocity and the crossflow direction was also investigated.

Optimisation of membrane area and energy requirement in tubular membrane modules

During ultrafiltration (UF), the driving force along the membrane is diminished due to concentration increase and frictional pressure drop. In most applications of ultrafiltration the influence of the frictional pressure drop is negligible. However, when treating concentrated, viscous liquids the frictional pressure drop can reduce the transmembrane pressure (TMP) significantly. The influence of cross-flow velocity and inlet pressure on flux and frictional pressure drop during concentration of retentate from the Stora Enso Nymölla pulp and paper mill ultrafiltration plant treating hardwood bleach plant effluent was studied in this work. The experimental data were used in a calculation tool to investigate the membrane area and energy requirement of two module design alternatives during concentration of the retentate in an additional stage. The first alternative is the same module design as in the existing plant on the hardwood line at Nymölla, where the tubular membranes in a module are connected in series. In the second alternative, the membrane tubes in a module were instead connected in parallel. The experimental flux increased markedly with increasing pressure and cross-flow velocity at all concentrations. However, the flux was significantly reduced when the chemical oxygen demand (COD) was increased. The flux was 120 l/m 2 h at 180 g/l and 23 l/m 2 h at 330 g/l (at 1.0 MPa and 4 m/s). The concentration was 180 and 330 g/l at volume reduction factor (VRF) 1 and 2. The calculated average flux was significantly higher in the design with membrane tubes in parallel. In addition, the flux was not only higher, but it also increased with increasing cross-flow velocity, whereas the flux in the design with membrane tubes in series reached a maximum flux at about 3 m/s.

Influence of cross-flow velocity on membrane performance during filtration of biological suspension

Through a new experimental procedure, the influence of cross-flow velocity on the formation of fouling layer during microfiltration (MF) and ultrafiltration (UF) of biological suspension with 5 g/l of mixed liquor suspended solids was studied. Based on the resistance-in-series model, filtration resistances caused by adsorption, concentration polarization, and reversible and irreversible fouling were determined. Each filtration resistance was compared with respect to the mass, thickness and density of the corresponding fouling layer (or foulants). Moreover, the effect of fouling layer on permeate quality was investigated. The obtained results showed that permeate flux increased linearly with increasing cross-flow velocity and a high cross-flow velocity was more effective to reduce fouling of MF membrane than that of UF membrane. The formation of a reversible fouling layer was actually prevented by a cross-flow velocity of 3.0 m/s for MF membrane and 2.0 m/s for UF membrane. In all cases, the magnitude of reversible and irreversible filtration resistances matched well the mass and thickness of their corresponding fouling layer. Along with its mass and thickness, the density of fouling layer was another important factor affecting filtration resistance and dissolved organic carbon (DOC) rejection. Distinct fouling layers as well as pore blocking and the narrowed pore itself were the major contributions for enhanced DOC rejection.

Ceramic membrane ultrafiltration of anionic and nonionic surfactant solutions

The ultrafiltration of two types of surfactants, sodium dodecyl sulfate (SDS, anionic) and Tergitol NP-9 (nonylphenol polyethylene glycol ether, nonionic), using a 20 nm ZrO 2 tubular membrane was investigated. The influence of crossflow velocity, temperature, pressure, and surfactant concentration on the permeate flux, close to and above the critical micelle concentration (CMC), is reported. Permeate flux and surfactant retention were measured in order to evaluate concentration polarization and fouling phenomena, and also the variation of these parameters due to surfactant/membrane interactions. High surfactant retentions (60–70%) were achieved depending on the feed concentration.

濃縮倍率とエネルギー効率を考慮したハチミツ限外ろ過

In the ultrafiltration of honey, filtration efficiency can not be expressed by permeate flux because it is necessary to dilute raw honey with water. Instead, rate of recovered sugar (RRS) which considers permeate flux and sugar content, was employed as an indicator of the filtration efficiency in this study.The effect of dilution on filtration efficiency was that RRS increased with a decrease in sugar content at initial stage of filtration. However, at concentration factor (CF) above 1.5, RRS at sugar content of 40% was higher than that at sugar content of 30%. This result was probably caused by changes in characteristics of suspended solids in raw honey due to dilution. In this case, the changes were small when the sugar content was 50%.The effect of operation temperature on filtration efficiency was shown that high RRS was observed at 50°C rather than 20°C and 30°C, however, temperature influenced cake resistance less than sugar content during filtration.The effects of operation pressure and cross-flow velocity on filtration efficiency were that when cross-flow velocity was 1.07-1.6 m/s, RRS increased as pressure increased. Whereas influence of cross-flow velocity on RRS decreased as pressure became decreased.Furthermore, total operation energy was easily calculated using inlet pressure under several filtration conditions to obtain a constant volume of permeate.At constant pressure, the cross-flow velocity was proportional to the energy. At constant cross-flow velocity, there were optimum pressures at each cross-flow velocity for useful filtration.

Intensified membrane filtration with corrugated membranes

Crossflow membrane microfiltration of 30% (w/w) water-in-oil emulsions is reported using hydrophobic PVDF and PTFE membranes. The flux performance of corrugated membranes is compared with that of flat membranes. The influence of crossflow velocity (CFV), flow channel height and transmembrane pressure (TMP) were investigated. The effect of varying the angle of corrugation (between the flow direction and the corrugation) on the overall flux performance was also examined. Experiments on flat and corrugated membranes have shown that increases in CFV and/or decreases in flow channel height result in an improved permeate flux caused by increased shear effects on the membrane surface. The use of corrugated membranes, however, enhanced the flux in a more efficient way by preferentially promoting turbulence near the membrane wall region, repeatedly mixing the boundary layer and hence reducing the concentration polarisation. The angle of corrugation was also found to have a marked effect on the flux. Flux increases of about 30, 100 and 160% in comparison with flat membranes was achieved for parallel, 45 and 90° angle of corrugation, respectively. It was illustrated that corrugations with angles of 45 and 90° can lead to a reduction in energy consumption of up to 80 and 88%, respectively. The TMP affected both the flux and the flux decline. The ‘breakthrough pressure’ at which both phases permeate through the membrane was found to be 1.5 bar. Membrane fouling behaviour is analysed and the applicability of filtration models to the experimental results identified. The fouling analysis revealed that the filtration process occurs in two distinct stages; initial pore blocking for 20 min followed by cake layer formation. The two stages can be best explained by a ‘cake filtration’ model.

An integrated flow reactor-membrane filtration system for heterogeneous photocatalysis. Part II: Experiments on the ultrafiltration unit and combined operation

A batch-recirculated photoreactor was combined with a hollow-fibre membrane ultrafiltration (UF) unit for heterogeneous photocatalysis applications. This paper focuses on the operation and modelling of the UF process component and on the performance of the integrated photoreactor–UF process assembly. Methylene blue and titanium dioxide (Degussa P-25) were used as the test pollutant and photocatalyst, respectively. The influence of cross-flow velocity, transmembrane pressure, and TiO2 dose on the permeate flux through the hollow fibre membrane is described. These data are modelled on the basis of concentration polarization and gel layer formation at the membrane surface/feed slurry boundary. The operation of the integrated photoreactor–UF assembly over ten repeat cycles is described. Photocatalyst separation was complete as gauged by nephelometric turbidity measurements. However, a systematic degradation in the photocatalyst performance was noted with each repeat cycle. Dynamic laser light scattering data are consistent with agglomeration of the TiO2 particles as a result of the UF process, and suggest a possible factor in the degraded photocatalytic activity. Possible solutions to this problem are finally presented.