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Flow Direction (flow + direction)

Distribution by Scientific Domains

Engineering	33%
Polymers and Materials Science	15%
Earth and Environmental Science	15%
Chemistry	11%
Medical Sciences	9%
Life Sciences	7%
Physics and Astronomy	3%
2 Other Domains	7%

Distribution within Engineering

Numerical Methods & Algorithms	27%
Power Technology & Power Engineering	18%

Selected Abstracts

Ophthalmic Artery Flow Direction on Color Flow Duplex Imaging Is Highly Specific for Severe Carotid Stenosis

JOURNAL OF NEUROIMAGING, Issue 1 2002
Patrick S. Reynolds MD
Background/Purpose. Collateral flow patterns are important risk factors for brain ischemia in the presence of internal carotid artery (ICA) stenosis or occlusion. Ophthalmic artery (OA) flow reversal, routinely studied by transcranial Doppler sonography, is an important marker for high-grade ICA stenosis or occlusion. The authors sought to define the value of assessing OA flow direction with color flow duplex ultrasonography (CDUS) in the setting of significant ICA disease. Methods. Of all patients having routine carotid ultrasound in the neurosonology laboratory between July 1995 and November 2000, 152 had both carotid and orbital (OA flow direction by reduced power orbital CDUS) examinations as well as angiographic confirmation of stenosis to which North American Symptomatic Carotid Endarterectomy Trial criteria could be applied. Degree of angiographic stenosis in these 152 patients (304 arteries) was correlated with OA flow direction. Results. Of 304 arteries, 101 had greater than 80% stenosis by angiogram. In 56 of these 101 arteries with high-grade stenosis or occlusion, the ipsilateral OA was reversed; however, OA flow direction was never reversed ipsilateral to arteries with less than 80% stenosis (sensitivity 55%, specificity 100%, negative predictive value 82%, and positive predictive value 100% for OA flow reversal as a marker of high-grade carotid lesions). Discussion/Conclusions. OA flow direction is easily studied with CDUS. Reversed OA flow direction is highly specific (100%) for severe ipsilateral ICA stenosis or occlusion, with excellent positive predictive value, moderate negative predictive value, and limited sensitivity. OA flow reversal is not only quite specific for severe ICA disease, which may be helpful if the carotid CDUS is difficult or inadequate, but may also provide additional hemodynamic insights (ie, the inadequacy of other collateral channels such as the anterior communicating artery). OA evaluation can provide important hemodynamic information and should be included as part of carotid CDUS if there is any evidence of ICA stenosis or occlusion. [source]

Design and implementation of a new neural network-based high speed distance relay

EUROPEAN TRANSACTIONS ON ELECTRICAL POWER, Issue 4 2008
M. Sanaye-Pasand
Abstract This paper presents a new neural network-based transmission line distance protection module. The proposed module uses samples of voltage and current signals to learn the hidden relationship existing in the input patterns. Using a power system model, simulation studies are preformed and influence of changing system parameters such as fault resistance and power flow direction is studied. The proposed neural network has also been implemented on a digital signal processor (DSP) board and its behavior is investigated using suitable developed hardware. Details of the implementation and experimental studies are given in the paper. Performance studies results show that the proposed algorithm is able to distinguish various transmission line faults rapidly and correctly. It shows that the proposed network is fast, reliable, and accurate. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Flow-field observations of a tidally driven island wake used by marine mammals in the Bay of Fundy, Canada

FISHERIES OCEANOGRAPHY, Issue 5 2007
D. W. JOHNSTON
Abstract Correlations between fine-scale oceanographic features and aggregations of marine mammals are frequently reported, but the physical forces shaping these relationships are rarely explored. We conducted a series of oceanographic observations and remote sensing surveys of an oceanographic feature near Grand Manan Island known to attract marine mammals on flood tides. We tracked drift drogues from cliff-top with a theodolite and conducted box-type surveys with an acoustic Doppler current profiler (ADCP) to assess flow patterns within the oceanographic feature. The feature was also visualized with Synthetic Aperture Radar (SAR) scenes. Drift drogues were advected towards a shear line originating near the northern tip of the island and entrained in one or more eddies downstream. ADCP surveys confirmed the presence of the shear line between rapid easterly flow and slower return flow. As the tide progressed, the shear line extended and manifested a single anti-cyclonic eddy at its distal end. As the flood tide progressed, northerly flow along the eastern shore of the island intensified and deflected the shear line northwards, shedding the eddy at slack high water. SAR images confirmed the presence of the shearline and eddy system, illustrating the evolution of a wake behind the island on flood tides. Profiles of flow direction and acoustic backscatter revealed secondary flows within the wake consistent with models and observations of other wakes. Oceanographic and remote sensing observations confirm that an island wake is generated by tidal flow past Grand Manan Island and provide an ecological context for the predictable aggregations of odontocete and mysticete cetaceans observed foraging within this region. [source]

From Micro to Meso: an exercise in determining hydraulic conductivity of fractured sandstone cores from detailed characterization of the fractures

GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2006
Salima Baraka-Lokmane
SUMMARY Hydraulic conductivities of fractured sandstone bore cores of 0.1 m in diameter are calculated using detailed characterization of the fracture geometry parameters determined using a resin casting technique. The accuracy of the measurements was about 0.25,1.25 ,m with the image size used. The values of the effective fracture apertures vary between 10 ,m and 50 ,m. For modelling purposes the samples are sectioned serially, perpendicular to the flow direction along the cylinder axis. The hydraulic conductivity of individual slices is estimated by summing the contribution of the matrix (assumed uniform) and each fracture (depending on its length and aperture). Finally, the hydraulic conductivity of the bulk sample is estimated by a harmonic average in series along the flow path. Results of this geometrical upscaling compare favourably with actual conductivity measured in hydraulic and pneumatic experiments carried out prior to sectioning. This study shows that the determination of larger-scale conductivity can be achieved, based on the evaluation of fracture geometry parameters (e.g. fracture aperture, fracture width and fracture length), measured using an optical method, at least at the laboratory scale. [source]

Effects of Measurement Error on Horizontal Hydraulic Gradient Estimates

GROUND WATER, Issue 1 2007
J.F. Devlin
During the design of a natural gradient tracer experiment, it was noticed that the hydraulic gradient was too small to measure reliably on an ,500-m2 site. Additional wells were installed to increase the monitored area to 26,500 m2, and wells were instrumented with pressure transducers. The resulting monitoring system was capable of measuring heads with a precision of ±1.3 × 10,2 m. This measurement error was incorporated into Monte Carlo calculations, in which only hydraulic head values were varied between realizations. The standard deviation in the estimated gradient and the flow direction angle from the x-axis (east direction) were calculated. The data yielded an average hydraulic gradient of 4.5 × 10,4±25% with a flow direction of 56° southeast ±18°, with the variations representing 1 standard deviation. Further Monte Carlo calculations investigated the effects of number of wells, aspect ratio of the monitored area, and the size of the monitored area on the previously mentioned uncertainties. The exercise showed that monitored areas must exceed a size determined by the magnitude of the measurement error if meaningful gradient estimates and flow directions are to be obtained. The aspect ratio of the monitored zone should be as close to 1 as possible, although departures as great as 0.5 to 2 did not degrade the quality of the data unduly. Numbers of wells beyond three to five provided little advantage. These conclusions were supported for the general case with a preliminary theoretical analysis. [source]

Simulations to Verify Horizontal Flow Measurements from a Borehole Flowmeter

GROUND WATER, Issue 3 2006
Scott C James
This paper reports on experiments and simulations of subsurface flow from a slotted acrylic tube deployed in a sand-tank flow chamber for two different purposes. In the first instance, the slotted tube is used to represent a single fracture intersected by an uncased well. In the second instance, the slotted tube is used to represent a multislot well screen within a porous medium. In both cases, the scanning colloidal borescope flowmeter (SCBFM) measures ground water velocity within the well by imaging colloids traveling through a well to measure their speed and direction. Measurements are compared against model simulations. For the case of a slotted tube representing a single fracture, SCBFM and model results agree with respect to the flow direction and to within a factor of 1.5 for the speed near the well's center. Model and experimental agreement lend confidence that for an uncased well drilled in a fractured-rock medium, a calibrated SCBFM could be used to identify and quantify flowing features. Next, the SCBFM was deployed in a four-column multislotted casing with slots aligned with the flow direction. Another numerical model was developed to estimate the flow field within this well screen to evaluate the potential usefulness of employing the SCBFM in a screened well to estimate flow speed and direction in the surrounding porous medium. Results indicate that if the slots are not aligned with the flow, the SCBFM may only provide order-of-magnitude speed measurements and direction measurements with an uncertainty of approximately ±25°. [source]

Influence of Transient Flow on Contaminant Biodegradation

GROUND WATER, Issue 2 2001
Mario Schirmer
The rate of biodegradation in contaminated aquifers depends to a large extent on dispersive mixing processes that are now generally accepted to result from spatial variations in the velocity field. It has been shown, however, that transient flow fields can also contribute to dispersive mixing. The influence of transient flow on biodegrading contaminants is particularly important since it can enhance mixing with electron acceptors, further promoting the reactive process. Using numerical simulations, the effect of transient flow on the behavior of a biodegradable contaminant is evaluated here both with respect to the development of apparently large horizontal transverse dispersion and also with respect to enhanced mixing between the substrate (electron donor) and electron acceptor. The numerical model BIO3D, which solves for advective-dispersive transport coupled with Monod-type biodegradation of substrates in the presence of an electron acceptor, was used for the simulations. The model was applied in a two-dimensional plan view mode considering a single substrate. Transient flow fields were found to yield larger apparent transverse dispersion because the longitudinal dispersivity also acts transverse to the mean flow direction. In the reactive case, the transient flow field increases substrate-oxygen mixing, which in turn enhances the overall rate of biodegradation. The results suggest that in the case of moderate changes of flow directions, a steady-state flow field can be justified, thereby avoiding the higher computational costs of a fully transient simulation. The use of a higher transverse horizontal dispersivity in a steady flow field can, under these conditions, adequately forecast plume development. [source]

Mechanism research of convective condensation heat transfer for a gas mixture flowing over a horizontal tube

HEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 2 2009
Li Jia
Abstract The modified film model combined with Nusselt's condensation theory are used for the study of convective condensation heat transfer on a horizontal tube with moist mixed horizontal gas flows at a given speed. A theoretical model considering gas boundary layer separation was set up. The liquid film flows and the heat transfer on the tube are presented. The effects of the flow direction on condensation heat transfer are discussed. The results predict that the condensate film is so thin that the liquid phase heat resistance can be ignored. © 2008 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20238 [source]

Transient flow patterns in a microfluidic chip with a complicated microstructure

HEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 4 2008
Wei Zhang
Abstract The transient flow patterns of the boiling flow in a microfluidic chip with a complicated microstructure were studied at low mass fluxes and high heat fluxes. The periodic flow pattern in the timescale of milliseconds and the stratified flow pattern were observed. For a specific separated zone, the liquid film thickness was increased along the flow direction and the dry-out always occurred earlier at the microchannel upstream rather than downstream. However, for different microchannel zones, the dry-out took place earlier in the downstream zone. It was determined that the low liquid Froude number was responsible for the formation of the stratified flow. The large boiling number resulted in a large shear stress at the vapor,liquid interface, leading to the accumulation of the liquid in the microchannel downstream, causing the increased liquid film thickness along the flow direction. © 2008 Wiley Periodicals, Inc. Heat Trans Asian Res, 37(4): 224,231, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20201 [source]

Simulating short-circuiting flow in a constructed wetland: the implications of bathymetry and vegetation effects

HYDROLOGICAL PROCESSES, Issue 6 2009
Joong-Hyuk Min
Abstract Short-circuiting flow, commonly experienced in many constructed wetlands, reduces hydraulic retention times in unit wetland cells and decreases the treatment efficiency. A two-dimensional (2-D), physically based, distributed modelling approach was used to systematically address the effects of bathymetry and vegetation on short-circuiting flow, which previously have been neglected or lumped in one-dimensional wetland flow models. In this study, a 2-D transient hydrodynamics with advection-dispersion model was developed using MIKE 21 and calibrated with bromide tracer data collected at the Orlando Easterly Wetland Cell 7. The estimated topographic difference between short-circuiting flow zone and adjacent area ranged from 0·3 to 0·8 m. A range of the Manning roughness coefficient at the short-circuiting flow zone was estimated (0·022,0·045 s m,1/3). Sensitivity analysis of topographical and vegetative heterogeneity deduced during model calibration shows that relic ditches or other ditch-shaped landforms and the associated sparse vegetation along the main flow direction intensify the short-circuiting pattern, considerably affecting 2-D solute transport simulation. In terms of hydraulic efficiency, this study indicates that the bathymetry effect on short-circuiting flow is more important than the vegetation effect. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Defining hydrochemical evolution of streamflow through flowpath dynamics in Kawakami headwater catchment, Central Japan

HYDROLOGICAL PROCESSES, Issue 10 2005
Kasdi Subagyono
Abstract The hydrochemical behaviour of catchments is often investigated by inferring stream chemistry through identification of source areas involved in hydrograph separation analysis, yet its dynamic evolution of hydrologic pathways has received little attention. Intensive hydrometric and hydrochemical measurements were performed during two different storms on March 29, 2001 and August 21,22, 2001 to define hydrochemical evolution under the dynamic of flow pathways in a 5·2 ha first-order drainage of the Kawakami experimental basin (KEB), Central Japan, a forested headwater catchment with various soil depths (1·8 to 5 m) overlying late Neogene of volcanic bedrocks. The hydraulic potential distribution and flow lines data showed that the change in flow direction, which was controlled by rainfall amount and antecedent wetness of the soil profile, agreed well with the hydrochemical change across the slope segment during the storm. Hydrograph separation predicted by end-member mixing analysis (EMMA) using Ca2+ and SiO2 showed that near surface riparian, hillslope soil water and deep riparian groundwater were important in stream flow generation. The evidence of decrease in solutes concentration at a depth of 1 m in the hillslope and 0·6 m in the near surface riparian during peak storm suggested a flushing of high solutes concentration. Most of the solutes accumulated in the deep riparian groundwater zone, which was due to prominent downward flow and agreed well with the residence time. The distinct flow pathways and chemistry between the near surface riparian and deep riparian groundwater zones and the linkage hillslope aquifer and near surface riparian reservoir, which controls rapid flow and solutes flushing during the storm event, are in conflict with the typical assumption that the whole riparian zone resets flow pathways and chemical signature of hillslope soil water, as has been reported in a previous study. Copyright © 2005 John Wiley & Sons, Ltd. [source]

A non-coaxial constitutive model for sand deformation under rotation of principal stress axes

INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 9 2008
Ali Lashkari
Abstract A constitutive model for the simulation of non-coaxiality, an aspect of anisotropic behavior of sand subjected to the rotation of the principal stress axes, is presented in this paper. Experimental studies have shown that non-coaxiality or non-coincidence of principal plastic strain increments with principal stress axes under loadings involving the rotation of principal stress axes may be considerable. Besides, the rotation of the principal stress axes results in dramatic effects on stiffness and dilatant behavior of sand. Therefore, the consequences of principal stress axes rotation on deformational behavior, dilatancy and soil stiffness must be taken into account in theoretical and practical problems. To this aim, the following steps are taken: (1) A general relationship for flow direction with respect to possibility of non-coaxial flow is developed. Moreover, special circumstances linking non-coaxiality to instantaneous interaction between loading and soil fabric are proposed. (2) Proposing novel expressions for plastic modulus and dilatancy function, the model is enforced to provide realistic simulations when sand is subjected to the rotation of the principal stress axes. Finally, with numerous examples and comparisons, the model capabilities are shown under various stress paths and drainage conditions. Copyright © 2007 John Wiley & Sons, Ltd. [source]

A shear-dilation-based model for evaluation of hydraulically stimulated naturally fractured reservoirs

INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 5 2002
M. K. Rahman
Abstract The role of shear dilation as a mechanism of enhancing fluid flow permeability in naturally fractured reservoirs was mainly recognized in the context of hot dry rock (HDR) geothermal reservoir stimulation. Simplified models based on shear slippage only were developed and their applications to evaluate HDR geothermal reservoir stimulation were reported. Research attention is recently focused to adjust this stimulation mechanism for naturally fractured oil and gas reservoirs which reserve vast resources worldwide. This paper develops the overall framework and basic formulations of this stimulation model for oil and gas reservoirs. Major computational modules include: natural fracture simulation, response analysis of stimulated fractures, average permeability estimation for the stimulated reservoir and prediction of an average flow direction. Natural fractures are simulated stochastically by implementing ,fractal dimension' concept. Natural fracture propagation and shear displacements are formulated by following computationally efficient approximate approaches interrelating in situ stresses, natural fracture parameters and stimulation pressure developed by fluid injection inside fractures. The average permeability of the stimulated reservoir is formulated as a function of discretized gridblock permeabilities by applying cubic law of fluid flow. The average reservoir elongation, or the flow direction, is expressed as a function of reservoir aspect ratio induced by directional permeability contributions. The natural fracture simulation module is verified by comparing its results with observed microseismic clouds in actual naturally fractured reservoirs. Permeability enhancement and reservoir growth are characterized with respect to stimulation pressure, in situ stresses and natural fracture density applying the model to two example reservoirs. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Turbulence in a three-dimensional wall-bounded shear flow

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 8 2010
A. Holstad
Abstract A new turbulent flow with distinct three-dimensional characteristics has been designed in order to study the impact of mean-flow skewing on the turbulent coherent vortices and Reynolds-averaged statistics. The skewing of a unidirectional plane Couette flow was achieved by means of a spanwise pressure gradient. Direct numerical simulations of the statistically steady Couette,Poiseuille flow enabled in-depth explorations of the turbulence field in the skewed flow. The imposition of a modest spanwise gradient turned the mean flow about 8° away from the original Couette flow direction and this turning angle remained nearly the same over the entire cross section. Nevertheless, a substantial non-alignment between the turbulent shear stress angle and the mean velocity gradient angle was observed. The structure parameter turned out to slightly exceed that in the pure Couette flow, contrary to the observations made in some other three-dimensional shear flows. Coherent flow structures, which are known to be associated with the Reynolds shear stress in near-wall regions, were identified by the ,2 -criterion. Instantaneous and ensemble-averaged vortices resembled those found in the unidirectional Couette flow. In the skewed flow, however, the vortex structures were turned to align with the local mean-flow direction. The conventional symmetry between Case 1 and Case 2 vortices was broken due to the mean-flow three-dimensionality. The turning of the coherent vortices and the accompanying symmetry-breaking gave rise to secondary and tertiary turbulent shear stress components. By averaging the already ensemble-averaged shear stresses associated with Case 1 and Case 2 vortices in the homogeneous directions, a direct link between the educed near-wall structures and the Reynolds-averaged turbulent stresses was established. These observations provide evidence in support of the hypothesis that the structural model proposed for two-dimensional turbulent boundary layers remains valid also in flows with moderate mean three-dimensionality. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Numerical calculations of erosion in an abrupt pipe contraction of different contraction ratios

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 1 2004
M. A. Habib
Abstract Erosion predictions in a pipe with abrupt contraction of different contraction ratios for the special case of two-phase (liquid and solid) turbulent flow with low particle concentration are presented. A mathematical model based on the time-averaged governing equations of 2-D axi-symmetric turbulent flow is used for the calculations of the fluid velocity field (continuous phase). The particle-tracking model of the solid particles is based on the solution of the governing equation of each particle motion taking into consideration the effect of particle rebound behaviour. Models of erosion were used to predict the erosion rate in mg/g. The effect of Reynolds number and flow direction with respect to the gravity was investigated for three contraction geometries considering water flow in a carbon steel pipe. The results show that the influence of the contraction ratio on local erosion is very significant. However, this influence becomes insignificant when the average erosion rates over the sudden contraction area are considered. The results also indicate the significant influence of inlet velocity variations. The influence of buoyancy is significant for the cases of low velocity of the continuous flow. A threshold velocity below which erosion may be neglected was indicated. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Calculation of turbulent fluid flow and heat transfer in ducts by a full Reynolds stress model

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 2 2003
Masoud Rokni
Abstract A computational method has been developed to predict the turbulent Reynolds stresses and turbulent heat fluxes in ducts by different turbulence models. The turbulent Reynolds stresses and other turbulent flow quantities are predicted with a full Reynolds stress model (RSM). The turbulent heat fluxes are modelled by a SED concept, the GGDH and the WET methods. Two wall functions are used, one for the velocity field and one for the temperature field. All the models are implemented for an arbitrary three-dimensional channel. Fully developed condition is achieved by imposing cyclic boundary conditions in the main flow direction. The numerical approach is based on the finite volume technique with a non-staggered grid arrangement. The pressure,velocity coupling is handled by using the SIMPLEC-algorithm. The convective terms are treated by the van Leer scheme while the diffusive terms are handled by the central-difference scheme. The hybrid scheme is used for solving the , equation. The secondary flow generation using the RSM model is compared with a non-linear k,, model (non-linear eddy viscosity model). The overall comparison between the models is presented in terms of the friction factor and Nusselt number. Copyright © 2003 John Wiley & Sons, Ltd. [source]

A parametric study of multi-phase and multi-species transport in the cathode of PEM fuel cells

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 8 2008
Nada Zamel
Abstract In this study, a mathematical model is developed for the cathode of PEM fuel cells, including multi-phase and multi-species transport and electrochemical reaction under the isothermal and steady-state conditions. The conservation equations for mass, momentum, species and charge are solved using the commercial software COMSOL Multiphysics. The catalyst layer is modeled as a finite domain and assumed to be composed of a uniform distribution of supported catalyst, liquid water, electrolyte and void space. The Stefan,Maxwell equation is used to model the multi-species diffusion in the gas diffusion and catalyst layers. Owing to the low relative species' velocity, Darcy's law is used to describe the transport of gas and liquid phases in the gas diffusion and catalyst layers. A serpentine flow field is considered to distribute the oxidant over the active cathode electrode surface, with pressure loss in the flow direction along the channel. The dependency of the capillary pressure on the saturation is modeled using the Leverette function and the Brooks and Corey relation. A parametric study is carried out to investigate the effects of pressure drop in the flow channel, permeability, inlet relative humidity and shoulder/channel width ratio on the performance of the cell and the transport of liquid water. An inlet relative humidity of 90 and 80% leads to the highest performance in the cathode. Owing to liquid water evaporation, the relative humidity in the catalyst layer reaches 100% with an inlet relative humidity of 90 and 80%, resulting in a high electrolyte conductivity. The electrolyte conductivity plays a significant role in determining the overall performance up to a point. Further, the catalyst layer is found to be important in controlling the water concentration in the cell. The cross-flow phenomenon is shown to enhance the removal of liquid water from the cell. Moreover, a shoulder/channel width ratio of 1:2 is found to be an optimal ratio. A decrease in the shoulder/channel ratio results in an increase in performance and an increase in cross flow. Finally, the Leverette function leads to lower liquid water saturations in the backing and catalyst layers than the Brooks and Corey relation. The overall trend, however, is similar for both functions. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Second-law analysis and optimization of microchannel flows subjected to different thermal boundary conditions

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 3 2005
Kuan Chen
Abstract Entropy generation and transfer in microchannel flows were calculated and analyzed for different thermal boundary conditions. Due to the small flow cross-sectional area, fluid temperature variation in the lateral direction was neglected and a laterally lumped model was developed and used in the first- and second-law analyses. Since the Peclet numbers of microchannel flows are typically low, heat conduction in the flow direction was taken into consideration. Computed fluid temperature and entropy generation rate were cast into dimensionless forms, thus can be applied to different fluids and channels of different sizes and configurations. Local entropy generation rate was found to be only dependent upon the temperature gradient in the flow direction. The optimization results of microchannel flows exchanging heat with their surroundings indicate the optimal fluid temperature distribution is a linear one. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Thermal performance analysis of a tube finned surface

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 4 2002
Kadir Bilen
Abstract The present work submits an experimental work on the heat transfer and friction loss characteristic, employing a tube finned heating surface kept at a constant temperature in a rectangular channel. The tube fins attached on the surface (o.d.=29 mm) were arranged as either in-line or staggered. The parameters for the study were Reynolds number (3700,30 000), depending on hydraulic diameter, the distance between the tube fins in the flow direction (Sy/D=1.72,3.45) and the fin arrangement. The change in the Nusselt number with these parameters was determined. For both tube fin arrangements, it was observed that increasing Reynolds number increased Nusselt number, and maximum heat transfer occurred at Sy/D=2.59. Thermal performances for both arrangements were also determined and compared with respect to heat transfer from the same surface without fins. With staggered array, a heat transfer enhancement up to 25 per cent for Sy/D=3.45 in staggered array was achieved in constant pumping power. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Design of irrigation water supply systems using the Q,C feasibility domain concept: I. Introduction and theory,

IRRIGATION AND DRAINAGE, Issue 1 2009
Gideon Sinai
irrigation; alimentation en eau; qualité de l'eau; systèmes d'irrigation; analyse de la contamination des réseaux; débit de l'eau Abstract The Q,C Feasibility Domain (QCFD) was defined and proposed as a tool for design of multiquality irrigation water supply systems. It determines all feasible combinations of water discharge and water quality, and can be represented by a point, a line, or an area in a diagram of water discharge versus solute flow rate (a Q,J diagram). The shape of the QCFD is the result of dilution of two or more flows from sources of different water quality. (assuming conservative substances) Several types of QCFDs were analyzed at sources, inner nodes of a network, and of consumer outlets. The effect of water discharge constraints (due to flow limitations in the network) on the QCFDs was formulated and analyzed. Computation of QCFDs of dilution junctions by vector addition of their inflows was described. The method was extended numerically to nonlinear mixing due to dependence of water salinity. Use of this method enables computation of QCFDs for inner nodes in networks, including dilution junctions. The effect of network topology and flow direction was discussed. Application and demonstration will follow in the next paper in this series. Copyright © 2008 John Wiley & Sons, Ltd. Le domaine de faisabilité Q,C (QCFD) a été défini et proposé comme un outil pour la conception des systèmes d'alimentation en eau d'irrigation de qualités multiples. Il détermine toutes les combinaisons faisables de débit et de qualité de l'eau, et peut être représenté par un point, une ligne, ou un secteur dans un diagramme débit-concentration (un diagramme de Q,J). La forme du QCFD est le résultat de la dilution de deux écoulements ou plus provenant de sources de qualité différente (en supposant la conservation des quantités). Plusieurs types de QCFD ont été analysés aux sources, n,uds, et sorties du réseau. L'effet des contraintes de débit (dues aux limitations dans le réseau) sur le QCFD a été formulé et analysé. On décrit le calcul de QCFD aux jonctions par l'addition des vecteurs d'apports. La méthode a été étendues numériquement aux mélanges non linéaires du fait de la liaison avec la salinité de l'eau. L'utilisation de cette méthode permet le calcul de QCFD aux n,uds intérieurs des réseaux, y compris les jonctions de dilution. L'effet de la topologie de réseau et du sens d'écoulement a été discuté. L'application et la démonstration suivront dans le prochain papier de cette série. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Spatially varied flow in non-prismatic channels.

IRRIGATION AND DRAINAGE, Issue 1 2002
I: dynamic equation
canal d'irrigation; modélisation; écoulement spatialement varié; équation de transfert; analyse numérique; expérimentation Abstract The bottom width of channels carrying spatially varied flow with increasing discharge is usually flared in the flow direction. This produces a non-prismatic section. This paper, based on the law of linear momentum conservation, presents a new form of the governing dynamic equation for flow in such circumstances. In addition to the computed water surface profile, the proposed equation affects the position of the control section and its flow depth as well. Copyright © 2002 John Wiley & Sons, Ltd. RÉSUMÉ La largeur du lit de cours d'eau, variée spatialement par l'augmentation du débit, influence la direction de l'écoulement. Cette procédure crée une coupe irréguliére de cours d'eau. Cet article présente une nouvelle forme de l'équation dynamique dans cette situation de l'écoulement. La méthodologie est basée sur la loi de conservation linéaire de momentum. L'équation proposée est capable de calculer le profil de niveau de l'eau. Elle affecte aussi sur la situation de coupe de contrôle et la profondeur de l'écoulement. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Rheological properties of LDPE processed by conventional processing machines

ADVANCES IN POLYMER TECHNOLOGY, Issue 3 2003
Masayuki Yamaguchi
Abstract The impact of applied processing history and the postprocessing annealing on the rheological properties of low-density polyethylene (LDPE) have been studied employing various kinds of conventional processing machines. Processing by a corotating twin-screw extruder (Co-TSE) and an internal batch mixer depressed the drawdown force, one of the elastic properties of a melt, to a great extent, even though molecular weight and the polydispersity did not change. On the other hand, the sample processed by a two-roll mill exhibited the drawdown force as high as the original pellets, which is owing to the intermittent stress history instead of the relentless one in the Co-TSE and the internal batch mixer. Furthermore, the effect of screw configuration in the Co-TSE has also been investigated. It was found that the processing by conveying screws depressed the drawdown force and melt fracture more than that by kneading blocks as long as the torque and the residence time are the same. The large, abrupt, and frequent change in flow direction in the Co-TSE with kneading blocks prohibits the molecular orientation, which leads to disentanglement associated with long-chain branches. © 2003 Wiley Periodicals, Inc. Adv Polym Techn 22: 179,187, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.10047 [source]

Rheological behavior of polymer melts in monodimensional flow through low-angle convergence and spiralling dies

ADVANCES IN POLYMER TECHNOLOGY, Issue 2 2001
L. Mascia
An experimental study was carried out to examine the rheological behavior of polymer melts in laminar flows through channels with small-angle convergences (2,3°) and spiralling walls (6°/mm along the flow direction), using an extrusion grade of low-density polyethylene. The results show that convergence is the main factor responsible for the observed deviations from steady state laminar shear flow, particularly with respect to additional pressure requirements to maintain a constant mass output. The swell ratio, calculated from the dimensions of the channel at the exit, was found to be considerably higher for flow-through converging channels. Only a small increase in swell ratio could be attributed, on the other hand, to the rotational elements of the die configuration. It is inferred that even for small angles of convergence the increased level of swelling is associated with elongational stress components, which were grouped together and denoted as the "additional stress." This was obtained from the difference between the calculated average shear stress at the wall, using the recorded pressure at the die entry, and the value of the average shear stress at the wall calculated from the shear viscosity data for the melt. © 2001 John Wiley & Sons, Inc. Adv Polym Techn 20: 99,107, 2001 [source]

On the flow-phase diagram for nematic liquid crystalline polymer under magnetic field

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2009
Shufang Fu
Abstract The effect of magnetic fields on molecular configuration of liquid crystalline polymers under shear flows are numerically analyzed using the extended Doi theory in which a molecular shape parameter is admitted. The evolution equation for the probability density function of the LCP molecules is directly solved without any closure approximations. One case is considered that the magnetic field makes 45° with respect to the flow direction. We can find that the magnetic fields strongly affect on the transition among flow-orientation modes, such as tumbling, wagging, and aligning modes. And a new aligning flow-orientation mode emerges at low shear rate, which is macroscopically same as the ordinary aligning mode, but is microscopically quite different from the ordinary one. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source]

Morphologies and mechanical properties of HDPE induced by small amount of high-molecular-weight polyolefin and shear stress produced by dynamic packing injection molding

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 4 2008
Zhanchun Chen
Abstract To better understand the effect of a small amount of high-molecular-weight polyethylene (HMWPE) on the mechanical properties and crystal morphology under the shear stress field, the dynamic packing injection molding (DPIM) was used to prepare the oriented pure polyethylene and its blends with 4% HMWPE. The experiment substantiated that the further improvement of tensile strength along the flow direction (MD) of high-density polyethylene (HDPE)/HMWPE samples was achieved, whereas the tensile strength along the transverse direction (TD) still substantially exceeded that of conventional molding. Tensile strength in both flow and TDs were highly enhanced, with improvements from 23 to 76 MPa in MD and from 23 to 31 MPa in TD, besides the toughness was highly improved. So, the samples of HDPE/HMWPE transformed from high strength and brittleness to high strength and toughness. The obtained samples were characterized via SEM and TEM. For HDPE/HMWPE, the lamellae of the one shish-kebab in the oriented region may be stretched into other shish-kebab structures, and one lamella enjoys two shish or even more. This unique crystal morphology could lead to no yielding and necking phenomena in the stress,strain curves of HDPE/HMWPE samples by DPIM. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

Morphological analysis of the tiger stripe on injection molding of polypropylene/ethylene-propylene rubber/talc blends dependent on based polypropylene design

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2007
Koki Hirano
Abstract Tiger stripe of injection molding of polypropylene (PP)/elastomer/talc blends was analyzed in terms of the morphology of the dispersed phase comprising elastomer components by using gloss and scanning electron microscopy (SEM). In addition, the contribution of the polymer design of PP, i.e., industrial block-type grade consisting of a homo-PP portion as the matrix and an ethylene propylene random copolymer portion as the domain is discussed. Local gloss measurement of the injected specimen along with the flow direction of the molten blends indicates a periodic fluctuation repeating higher and lower degrees of gloss, corresponding to the period of glossy and cloudy portions of the tiger stripe, respectively. These local gloss degrees are highly dependent on the morphologies of the dispersed phases near the surface layer of the injected specimen. The gloss increases when the ratio long axis (L) and diameter (D), L/D, of the dispersed phase are increased, and the gloss decreases when the L/D is decreased. Increasing the intrinsic viscosity of the ethylene-propylene rubber portion of the PP is an effective design factor for restricting the deformation against shear strain during injection process by giving the dispersed phases high elasticity. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 192,199, 2007 [source]

Mechanotransduction in endothelial cell migration

JOURNAL OF CELLULAR BIOCHEMISTRY, Issue 6 2005
Song Li
Abstract The migration of endothelial cells (ECs) plays an important role in vascular remodeling and regeneration. EC migration can be regulated by different mechanisms such as chemotaxis, haptotaxis, and mechanotaxis. This review will focus on fluid shear stress-induced mechanotransduction during EC migration. EC migration and mechanotransduction can be modulated by cytoskeleton, cell surface receptors such as integrins and proteoglycans, the chemical and physical properties of extracellular matrix (ECM) and cell,cell adhesions. The shear stress applied on the luminal surface of ECs can be sensed by cell membrane and associated receptor and transmitted throughout the cell to cell,ECM adhesions and cell,cell adhesions. As a result, shear stress induces directional migration of ECs by promoting lamellipodial protrusion and the formation of focal adhesions (FAs) at the front in the flow direction and the disassembly of FAs at the rear. Persistent EC migration in the flow direction can be driven by polarized activation of signaling molecules and the positive feedback loops constituted by Rho GTPases, cytoskeleton, and FAs at the leading edge. Furthermore, shear stress-induced EC migration can overcome the haptotaxis of ECs. Given the hemodynamic environment of the vascular system, mechanotransduction during EC migration has a significant impact on vascular development, angiogenesis, and vascular wound healing. J. Cell. Biochem. © 2005 Wiley-Liss, Inc. [source]

A review of hand-washing techniques in primary care and community settings

JOURNAL OF CLINICAL NURSING, Issue 6 2009
Sheree MS Smith
Aim., This review seeks to identify the most effective hand-washing and hand-cleansing practice that could be used in primary care. Background., Healthcare associated infection is a major problem in the UK causing 5000 deaths every year. Current guidelines indicate expert opinion is the level of evidence for hand washing as an activity to reduce infection. Design., Systematic review. Method., Publications on hand-washing, hand-cleansing studies, policy and practice-based documents were sought by searching several databases. Terms used included hand washing, hand cleansing, hand hygiene, hand decontamination, infection control and primary care. Results., Few articles described the hand-washing technique in detail and some publications simply referred to either the European and British Standards or the Centre for Disease Control statement on hand washing. Major discrepancies in hand position and water flow direction were found. Several methodological problems were also identified and few studies were undertaken in primary care. Conclusion., This review has found a lack of evidence for hand-washing techniques being undertaken in practice today. Findings from hand-washing technique studies were inconclusive and methodological issues exist resulting in sparse reliable evidence. There is an urgent need to undertake methodologically sound studies of hand-washing techniques for use in the ever expanding scope of primary care practice. Relevance to clinical practice., Evidence for hand-washing and hand-cleansing techniques will inform healthcare professional practice, and contribute to the overall management of infection control in primary care. [source]

NETmix®, a new type of static mixer: Modeling, simulation, macromixing, and micromixing characterization

AICHE JOURNAL, Issue 9 2009
Paulo E. Laranjeira
Abstract NETmix® is a new technology for static mixing based on a network of chambers connected by channels. The NETmix® model is the basis of a flow simulator coupled with chemical reaction used to characterize macro and micromixing in structured porous media. The chambers are modeled as perfectly mixing zones and the channels as plug flow perfect segregation zones. A segregation parameter is introduced as the ratio between the channels volume and the whole network volume. Different kinetics and reactants injection schemes can be implemented. Results show that the number of rows in the flow direction and the segregation parameter control both macro and micromixing, but the degree of micromixing is also controlled by the reactants injection scheme. The NETmix® model enables the systematic study of micromixing and macromixing for different network structures and reaction schemes, enabling the design of network structures to ensure the desired yield and selectivity. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source]