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Liquid Flow (liquid + flow)
Terms modified by Liquid Flow Selected AbstractsModeling and Numerical Simulation of Cavitation for Compressible Liquid FlowPROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2003A. Berg A method for the numerical simulation of cavitation phenomena based on the thermodynamic properties of liquid and steam is described. Thereby, a homogeneous cavitation model using a fully compressible discretization technique is considered. The ability of the scheme is proven by numerical experiments. [source] Two-phase flow in structured packings: Modeling and calculation on a macroscopic scaleAICHE JOURNAL, Issue 3 2008B. Mahr Abstract A model is presented that allows calculating the macroscopic flow field of counter-current two-phase flow in strongly anisotropic porous structures. It is applied to corrugated structured packings. All flow field variables and packing properties are averaged over the volume of an elementary cell. The anisotropic gas flow resistance is derived from measurements and from separate CFD calculations on 3D-X-ray CT scans. The liquid's flow resistance is calculated using an analytical model of liquid film flow on an inclined plate. Liquid flow along both preferential flow directions is represented by two separate phases, in order to consider horizontal forces despite their symmetry. Gas-liquid momentum transfer above the loading point is included. The macroscopic flow field is calculated for a 288 mm I.D. column containing four packing elements. Liquid spreading from a point source, for uniform irrigation, increased hold-up at the packing elements' joints and pressure drop are tested against experimental results. © 2008 American Institute of Chemical Engineers AIChE J, 2008 [source] Liquid flow in capillary (electro)chromatography: Generation and control of micro- and nanoliter volumesJOURNAL OF SEPARATION SCIENCE, JSS, Issue 6-7 2003Erdmann Rapp Abstract We describe and discuss instrumental developments in capillary (electro)chromatography which are of particular relevance for generating (and controlling) required volumetric flow rates in the micro- and nanoliter range through packed capillaries. Both isocratic and gradient elution are considered. For capillary HPLC this practically involves only commercial instrumentation, with systems based on syringe or piston pumps, but it also realizes the innovative concept of a high-pressure electrokinetic pump. The numerous systems that have been used to generate electroosmotic flow through chromatographic beds are classified under the following headings: i) basically commercial capillary electrophoresis instruments (adapted for electrochromatography); ii) home-built configurations; and iii) commercial capillary electrochromatography systems. Concerning the reviewed instrumentation, emphasis is placed on feasibility, automation, as well as system-inherent delay times and dead volumes. [source] Fluid flow in an impacting symmetrical tee junction II: two-phase air/water flowASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 4 2009A. P. Doherty Abstract A universal flow regime map was presented for two-phase flow in a horizontal pipe. Data were given on two-phase gas/liquid flow in a symmetrical impacting tee junction. The flow regimes in the inlet arm of the tee were those expected for a straight pipe. This was not so for the outlet arm where, in most cases, flow regimes occurred earlier than expected. At low liquid outlet flows the stratified regime was reinforced into higher gas flows than expected. The liquid hold-up exhibited variations over the tee junction. The pressure drop in the inlet arm agreed with similar data for the straight pipe, but in the tee outlets was below that expected for the straight pipe. The tee junction pressure drop showed some parallels to the corresponding single-phase flow data but the le/d dimensionless values for the junction pressure drop showed a wide variation, in contrast to the single-phase junction data. A model was presented based on the Lockhard,Martinelli theory that enabled the tee pressure drop to be predicted. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Numerical studies of electrokinetic control of DNA concentration in a closed-end microchannelELECTROPHORESIS, Issue 5 2010Yasaman Daghighi Abstract A major challenge in lab-on-a-chip devices is how to concentrate sample molecules from a dilute solution, which is critical to the effectiveness and the detection limit of on-chip bio-chemical reactions. A numerical study of sample concentration control by electrokinetic microfluidic means in a closed-end microchannel is presented in this paper. The present method provides a simple and efficient way of concentration control by using electrokinetic trapping of a charged species of interest, controlling liquid flow and separating different sample molecules in the microchannel. The electrokinetic-concentration process and the controlled transport of the sample molecules are numerically studied. In this system, in addition to the electroosmotic flow and the electrophoresis, the closed-end of the chamber causes velocity variation at both ends of the channel and induces a pressure gradient and the associated fluid movement in the channel. The combined effects determine the final concentration field of the sample molecules. The influences of a number of parameters such as the channel dimensions, electrode size and the applied electric field are investigated. [source] Speciation of selenium compounds by open tubular capillary electrochromatography-inductively coupled plasma mass spectrometryELECTROPHORESIS, Issue 21 2006Shu-Yu Lin Abstract We introduce a T-type interface and a crossflow nebulizer to find ways to combine CEC with inductively coupled plasma MS (ICP-MS) detection for selenium speciation. For CEC separation, we employed a macrocyclic polyamine-bonded phase capillary as the separation column and a bare fused-silica capillary filled with the make-up liquid (0.05,M,HNO3). The effect of nebulizer gas flow rate, make-up liquid flow, type, concentration and pH of the mobile phase on the separation have been studied. Tris buffer of 50,mM at pH,8.50 gave the best performance for selenium speciation. The reproducibility of the retention time indicated that sample injection by electrokinetic and nebulizer gas flow was better than that by self-aspiration alone. The detection limits for selenate, selenite, selenocystine and selenomethionine were found to be 2.40, 3.53, 12.86 and 11.25,ng/mL, respectively. Due to the high sensitivity and element-specific detection, as well as the high selectivity of the bonded phase, quantitative analysis of selenium speciation in urine was also achieved. [source] 1-D numerical modelling of shallow flows with variable horizontal densityINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 11 2010Feifei Zhang Leighton Abstract A1-D numerical model is presented for vertically homogeneous shallow flows with variable horizontal density. The governing equations represent depth-averaged mass and momentum conservation of a liquid,species mixture, and mass conservation of the species in the horizontal direction. Here, the term ,species' refers to material transported with the liquid flow. For example, when the species is taken to be suspended sediment, the model provides an idealized simulation of hyper-concentrated sediment-laden flows. The volumetric species concentration acts as an active scalar, allowing the species dynamics to modify the flow structure. A Godunov-type finite volume scheme is implemented to solve the conservation laws written in a deviatoric, hyperbolic form. The model is verified for variable-density flows, where analytical steady-state solutions are derived. The agreement between the numerical predictions and benchmark test solutions illustrates the ability of the model to capture rapidly varying flow features over uniform and non-uniform bed topography. A parameter study examines the effects of varying the initial density and depth in different regions. Copyright © 2009 John Wiley & Sons, Ltd. [source] Coupled lattice-Boltzmann and finite-difference simulation of electroosmosis in microfluidic channelsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 5 2004Dzmitry Hlushkou Abstract In this article we are concerned with an extension of the lattice-Boltzmann method for the numerical simulation of three-dimensional electroosmotic flow problems in porous media. Our description is evaluated using simple geometries as those encountered in open-channel microfluidic devices. In particular, we consider electroosmosis in straight cylindrical capillaries with a (non)uniform zeta-potential distribution for ratios of the capillary inner radius to the thickness of the electrical double layer from 10 to 100. The general case of heterogeneous zeta-potential distributions at the surface of a capillary requires solution of the following coupled equations in three dimensions: Navier,Stokes equation for liquid flow, Poisson equation for electrical potential distribution, and the Nernst,Planck equation for distribution of ionic species. The hydrodynamic problem has been treated with high efficiency by code parallelization through the lattice-Boltzmann method. For validation velocity fields were simulated in several microcapillary systems and good agreement with results predicted either theoretically or obtained by alternative numerical methods could be established. Results are also discussed with respect to the use of a slip boundary condition for the velocity field at the surface. Copyright © 2004 John Wiley & Sons, Ltd. [source] Elastohydrodynamics of tensioned web roll coating processINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 6 2003M. S. Carvalho Abstract Coating process is an important step in the manufacturing of different products, such as paper, adhesive and magnetic tapes, photographic films, and many other. The tensioned web roll coating is one the several methods used by different industries. It relies on the elastohydrodynamic action between the fluid and the tensioned substrate for transferring and applying the liquid. The main advantage of this method is its ability to apply very thin liquid layers with less sensitivity to mechanical tolerance at relative small cost. Despite its industrial application, theoretical analysis and fundamental understanding of the process are limited. This work analyses this elastohydrodynamic action by solving the differential equations that govern the liquid flow, described by the Navier,Stokes equation, and the web deformation, modelled by the cylindrical shell approximation. The goal is to determine the operating conditions at which the process is two dimensional and defect free. The equations are discretized by the Galerkin/finite-element method. The resulting non-linear system of equations is solved by Newton's method coupled with pseudo-arc-length continuation in order to obtain solutions around turning points. The theoretical results are used to construct an operating window of the process that is in agreement with limited experimental data. Copyright © 2003 John Wiley & Sons, Ltd. [source] The effect of gas-liquid counter-current operation on gas hold-up in bubble columns using electrical resistance tomography,JOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 9 2010Haibo Jin Abstract BACKGROUND: In order to improve the performance of a counter-current bubble column, radial variations of the gas hold-ups and mean hold-ups were investigated in a 0.160 m i.d. bubble column using electrical resistance tomography with two axial locations (Plane 1 and Plane 2). In all experiments the liquid phase was tap water and the gas phase air. The superficial gas velocity was varied from 0.02 to 0.25 m s,1, and the liquid velocity varied from 0 to 0.01 m s,1. The effect of liquid velocity on the distribution of mean hold-ups and radial gas hold-ups is discussed. RESULTS: The gas hold-up profile in a gas,liquid counter-current bubble column was determined by electrical resistance tomography. The liquid velocity slightly influences the mean hold-up and radial hold-up distribution under the selected operating conditions and the liquid flow improves the transition gas velocity from a homogeneous regime to a heterogeneous regime. Meanwhile, the radial gas hold-up profiles are steeper at the central region of the column with increasing gas velocity. Moreover, the gas hold-up in the centre of the column becomes steeper with increasing liquid velocity. CONCLUSIONS: The value of mean gas hold-ups slightly increases with increasing downward liquid velocity, and more than mean gas hold-ups in batch and co-current operation. According to the experimental results, an empirical correlation for the centreline gas hold-up is obtained based on the effects of gas velocity, liquid velocity, and ratio of axial height to column diameter. The values calculated in this way are in close agreement with experimental data, and compare with literature data on gas hold-ups at the centre of the column. Copyright © 2010 Society of Chemical Industry [source] Agitation requirements for complete solid suspension in an unbaffled agitated vessel with an unsteadily forward,reverse rotating impellerJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 7 2007Shuichi Tezura Abstract Background: To develop a new type of solid,liquid apparatus, we have proposed the application of an agitation system with an impeller whose rotation alternates direction unsteadily, i.e., a forward,reverse rotating impeller. For an unbaffled agitated vessel fitted with this system, the suspension of solid particles in a liquid was studied using a disk turbine impeller with six flat blades. Results: The effects of the solid,liquid conditions and geometrical conditions of the apparatus on the minimum rotation rate and the corresponding impeller power consumption were evaluated experimentally for a completely suspended solid. The power consumption for a just suspended solid with this type of vessel was comparable with that for a baffled vessel with a unidirectionally rotating impeller, taking the liquid flow along the vessel bottom into consideration. Conclusion: Empirical relationships to predict the parameters of agitation requirements were found. A comparative investigation demonstrated the usefulness of the forward,reverse rotation mode of the impeller for off-bottom suspension of solid particles. Copyright © 2007 Society of Chemical Industry [source] CFD simulations of hydrodynamic/thermal coupling phenomena in a bubble column with internalsAICHE JOURNAL, Issue 9 2010Cédric Laborde-Boutet Abstract CFD simulations have been carried out in a full three-dimensional, unsteady, Eulerian framework to simulate hydrodynamic/thermal coupling in a bubble column with internals. A first part of the study, dedicated to the hydrodynamic/thermal coupling in liquid single-phase flows, showed that assuming constant wall temperature on the internals constitutes a reasonable approximation in lieu of comprehensive simulations encompassing shell flow and coolant flow together. A second part dealing with the hydrodynamics of gas,liquid flows in a bubble column with internals showed that a RNG k,, turbulence model formulation accounting for gas-induced turbulence was a relevant choice. The last part used these conclusions to build a hydrodynamic/thermal coupling model of a gas,liquid flow in a bubble column with internals. With a per-phase RNG k,, turbulence model and assuming constant wall temperature, it was possible to simulate heat transfer phenomena consistent with experimentally measured heat transfer coefficients. © 2010 American Institute of Chemical Engineers AIChE J, 2010 [source] Two-phase flow behavior in microtube reactors during biodiesel production from waste cooking oilAICHE JOURNAL, Issue 5 2010Guoqing Guan Abstract Flow patterns in the course of transesterification of waste cooking oil (WCO), sunflower oil (SFO) with water and/or oleic acid as a model of WCO, and pure SFO in the presence of a KOH catalyst in microtubes were investigated. FAME yield for the transesterification of WCO reached more than 89% in the microtube reactors with a residence time of 252 s at 333 K. The flow patterns when using WCO were changed from a liquid,liquid slug flow at the inlet region to a parallel flow at the middle region, and then to a homogeneous liquid flow at the outlet region as the reaction proceeded at 333 K. Fine droplets containing glycerol and methanol generally formed in oil slugs when using pure SFO, but were almost unobservable when using WCO. The soap produced from free fatty acids was considered to be the main factor affecting the flow patterns of WCO and SFO. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Hydrodynamics and mass transfer of gas,liquid flow in a falling film microreactorAICHE JOURNAL, Issue 5 2009Haocui Zhang Abstract In this article, flow pattern of liquid film and flooding phenomena of a falling film microreactor (FFMR) were investigated using high-speed CCD camera. Three flow regimes were identified as "corner rivulet flow," "falling film flow with dry patches," and "complete falling film flow" when liquid flow rate increased gradually. Besides liquid film flow in microchannels, a flooding presented as the flow of liquid along the side wall of gas chamber in FFMR was found at high liquid flow rate. Moreover, the flooding could be initiated at lower flow rate with the reduction of the depth of the gas chamber. CO2 absorption was then investigated under the complete falling flow regime in FFMR, where the effects of liquid viscosity and surface tension on mass transfer were demonstrated. The experimental results indicate that kL is in the range of 5.83 to 13.4 × 10,5 m s,1 and an empirical correlation was proposed to predict kL in FFMR. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Prediction of two-phase flow distribution in parallel pipes using stability analysisAICHE JOURNAL, Issue 10 2006L. Pustylnik Abstract Two-phase gas liquid flow in pipes is a complex process. One of the problems that is hardly understood is how the two phases are distributed among two or more parallel lines with a common inlet manifold. Steady-state analysis yields multiple steady-state solutions. Linear and nonlinear (simulation) stability analyses are performed in order to determine the actual distribution of the flow that will take place in a real system. The analysis shows that when there are four parallel pipes, for example, the two-phase flow mixture from the common inlet manifold can choose to flow in one, two, three, or in all four pipes, depending on the flow rates of the liquid, and the gas and on the pipes inclination. For low-flow rates of gas and liquid, the flow tends to take place only in one line, while stagnant liquid columns are present in the other three pipes. As the flow rate increases the flow will take place in 2, 3 and finally in 4 pipes. Experimental data confirm the analysis although matching is only approximate. © 2006 American Institute of Chemical Engineers AIChE J, 2006 [source] Lateral dispersion in liquid flow through packed beds at Pem < 1,400AICHE JOURNAL, Issue 5 2000J. R. F. Guedes de Carvalho First page of article [source] Two-phase flow electrosynthesis: Comparing N -octyl-2-pyrrolidone,aqueous and acetonitrile,aqueous three-phase boundary reactionsJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 1 2009Stuart M. MacDonald Abstract A microfluidic double channel device is employed to study reactions at flowing liquid,liquid junctions in contact with a boron-doped diamond (BDD) working electrode. The rectangular flow cell is calibrated for both single-phase liquid flow and biphasic liquid,liquid flow for the case of (i) the immiscible N -octyl-2-pyrrolidone (NOP),aqueous electrolyte system and (ii) the immiscible acetonitrile,aqueous electrolyte system. The influence of flow speed and liquid viscosity on the position of the phase boundary and mass transport-controlled limiting currents are examined. In contrast to the NOP,aqueous electrolyte case, the acetonitrile,aqueous electrolyte system is shown to behave close to ideal without ,undercutting' of the organic phase under the aqueous phase. The limiting current for three-phase boundary reactions is only weakly dependent on flow rate but directly proportional to the concentration and the diffusion coefficient in the organic phase. Acetonitrile as a commonly employed synthetic solvent is shown here to allow effective three-phase boundary processes to occur due to a lower viscosity enabling faster diffusion. N -butylferrocene is shown to be oxidised at the acetonitrile,aqueous electrolyte interface about 12 times faster when compared with the same process at the NOP,aqueous electrolyte interface. Conditions suitable for clean two-phase electrosynthetic processes without intentionally added supporting electrolyte in the organic phase are proposed. Copyright © 2008 John Wiley & Sons, Ltd. [source] Advanced models for erosion corrosion and its mitigation,MATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 2 2008G. Schmitt Erosion corrosion, i.e., flow-induced localized corrosion (FILC) is initiated when flow dynamic forces surpass the fracture energy of protective layers or scales on metals. With a new model the maximum interaction energies between flowing media and solid walls can be quantified in terms of "freak" energy densities created during singular events (freak events) of perpendicular impacts by near-wall microturbulence elements. The freak energy densities are in the megaPascal range and match well in the order of magnitude with fracture energies of protective layers and can be estimated from Wavelet diagnostics of electrochemical current noise measured at microelectrodes under mass transport controlled conditions. This solves the problem that wall shear stresses, generally used to quantify critical flow intensities for FILC initiation, range several orders of magnitude (Pa range) below the fracture energies of protective layers. The new advanced model allows for the first time to quantify the maximum fluid dynamic forces exerted on solid walls under different turbulent and disturbed flow conditions (one-phase liquid flow on jet impinged surfaces and on coupons in rotated cages, surfaces impacted by slug flow and gas-pulsed impinging jets). Drag reducing additives were shown to reduce freak energy densities to values significantly below fracture energies of protective layers and hence inhibit initiation of FILC. The onset of FILC can be monitored online with the newly developed CoulCount method, an easy-to-use, non-invasive diagnostic tool which evaluates electrochemical current noise between jet impinged electrode pairs made from the metals to be tested. [source] Direct meso-scale simulations of fibres in turbulent liquid flowTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 4 2010J. J. Derksen Abstract A procedure for direct, meso-scale simulations of flexible fibres immersed in liquid flow is introduced. The fibres are composed of chains of spherical particles connected through ball joints with the bending stiffness of the joints as a variable. The motion of the fibres and the liquid is two-way coupled with full resolution of the solid,liquid interface. First the simulation procedure is validated by means of an analytical solution for sphere doublets in zero-Reynolds simple shear flow. Subsequently we use the numerical method to study inertial flows with fibres, more specifically the interaction of a fibre with isotropic turbulence. Une procédure pour des simulations directes à la méso-échelle de fibres souples immergées dans la circulation de liquide est présentée. Les fibres sont composées de chaînes de particules sphériques reliées par des joints à rotule avec la rigidité à la flexion des joints comme variable. Le mouvement des fibres et du liquide est bidirectionnel avec une résolution intégrale de l'interface solide-liquide. D'abord, la procédure de simulation est validée au moyen d'une solution analytique pour les doublets de sphère dans un écoulement de cisaillement simple à nombre de Reynolds nul. Par la suite, nous utilisons la méthode numérique pour étudier les flux inertiels avec les fibres, plus précisément l'interaction d'une fibre avec la turbulence isotrope. [source] Effect of impeller clearance on liquid flow within an unbaffled vessel agitated with a forward,reverse rotating impellerTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 6 2009Masanori Yoshida Abstract For an unbaffled agitated vessel with an unsteadily forward,reverse rotating impeller whose rotation proceeds with repeated acceleration, deceleration, and stop,reverse processes, liquid flow was studied through visualisation and measurement using particle tracking velocimetry (PTV). A disk turbine impeller with six flat blades was used with varied height settings. The impeller clearance and its forward,reverse rotation cycle characterised the impeller region flow: the radially outward flow in the deceleration process for the larger clearance relative to the vessel diameter of 1/3, and the axially downward flow in the acceleration process for the smaller clearance relative to the vessel diameter of 1/8. The flow patterns within the vessel resulting from the impeller's larger and smaller clearances were outlined, respectively, by double loops and a single loop of circulation, resembling the pattern produced by unidirectionally rotating turbine-type impellers. The discharge flow was revealed to contain a comparable level of periodic circumferential velocity component, irrespective of the impeller clearance. On a étudié l'écoulement liquide par visualisation et mesure en utilisant la vélocimétrie avec poursuite de trajectoire pour une cuve non compartimentée et agitée avec un agitateur rotatif avant-arrière non stable dont la rotation est composée de périodes répétées d'accélération, de ralentissement et d'arrêt-marche arrière. Un agitateur à six pales plates a été utilisé avec quatre réglages de hauteur différents. Le dégagement de l'agitateur et son cycle de rotation avant-arrière caractérisaient l'écoulement liquide dans la région de l'agitateur : l'écoulement radial vers l'extérieur dans le processus de décélération pour le dégagement le plus important par rapport au diamètre de la cuve de 1/3 et l'écoulement axial vers le bas dans le processus d'accélération pour le dégagement le plus petit par rapport au diamètre de la cuve de 1/8. Les modèles d'écoulement intérieurs de la cuve résultant du plus grand et du plus petit dégagements de l'agitateur ont été décrits, respectivement, par des doubles boucles et une simple boucle de circulation, ce qui ressemble au modèle produit par des agitateurs à hélice unidirectionnels. On a révélé que l'écoulement de sortie contenait un niveau comparable de vélocité périodique périphérique, indépendamment du dégagement de l'agitateur. [source] Oil,water two-phase flow in microchannels: Flow patterns and pressure drop measurementsTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 6 2008Abdelkader Salim Abstract This paper investigates oil,water two-phase flows in microchannels of 793 and 667 µm hydraulic diameters made of quartz and glass, respectively. By injecting one fluid at a constant flow rate and the second at variable flow rate, different flow patterns were identified and mapped and the corresponding two-phase pressure drops were measured. Measurements of the pressure drops were interpreted using the homogeneous and Lockhart,Martinelli models developed for two-phase flows in pipes. The results show similarity to both liquid,liquid flow in pipes and to gas,liquid flow in microchannels. We find a strong dependence of pressure drop on flow rates, microchannel material, and the first fluid injected into the microchannel. On étudie dans cet article les écoulements diphasiques huile-eau dans des micro-canaux de 793 µm et 667 µm de diamètre hydraulique faits de quartz et de verre, respectivement. En injectant un fluide à un débit constant et le second à un débit variable, différents schémas d'écoulements ont été observés et représentés en diagrammes, et les pertes de charge diphasiques correspondantes ont été mesurées. Les mesures de perte de charge ont été interprétées à l'aide du modèle homogène et du modèle de Lockhart,Martinelli mis au point pour les écoulements diphasiques dans les conduites. Les résultats montrent une similarité à la fois avec l'écoulement liquide-liquide et l'écoulement liquide de gaz dans des micro-canaux. On a trouvé une forte dépendance de la perte de charge aux débits, au matériau des micro-canaux et au premier fluide injecté dans le micro-canal. [source] Effect of radial angle on mixing time for a double jet mixerASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2010P. Manjula Abstract Mixing is one of the common unit operations employed in chemical industries. It is used for blending of liquids, flocculation, homogenization of mixtures, ensuring proper heat and mass transfer in various operations, prevention of deposition of solid particles, etc. Earlier research aspects were focused on experimental estimation of mixing time and proposing suitable correlations for the prediction of mixing time, the recent one being on flow visualization. However, most of the results reported in the literature deal with liquid flow with multi jets, whereas the effect of radial angle on mixing time was not studied. This study describes the effect of radial angle on mixing time as determined by experiment and simulation. A computational fluid dynamics (CFD) modeling is done for a jet mixing tank having two jets for a water,water system. Nozzle configuration for jet1 was fixed on the basis of our earlier studies (2/3rd position, flow rate 9l/m, nozzle angle 45° and nozzle diameter 10 mm). Mixing times were estimated for different jet2 configurations (jet angle 30°, 45° and 60°; radial angles 60°, 120°, 180°) located at different tank heights (2/3rd and 1/3rd from the bottom of the tank). The results obtained for mixing time for jet mixing in a tank with two jets are analyzed and the suitable nozzle angle, radial angle and position are proposed for the jet2 of the jet mixer considered in the present study. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Simulation and analysis of flow through microchannelASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 4 2009Madhusree Kundu Abstract One-dimensional and two-dimensional models for microchannel flow with noncontinuum (slip flow) boundary conditions have been presented here. This study presents an efficient numerical procedure using pressure-correction-based iterative SIMPLE algorithm with QUICK scheme in convective terms to simulate a steady incompressible two-dimensional flow through a microchannel. In the present work, the slip flow of liquid through a microchannel has been modeled using a slip length assumption instead of using conventional Maxwell's slip flow model, which essentially utilizes the molecular mean free path concept. The models developed, following this approach, lend an insight into the physics of liquid flow through microchannels. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Interaction of biofilm structure and bulk liquid flowBIOTECHNOLOGY & BIOENGINEERING, Issue 1 2010Article first published online: 16 JUL 2010 No abstract is available for this article. [source] Hairy Root Culture in a Liquid-Dispersed Bioreactor: Characterization of Spatial HeterogeneityBIOTECHNOLOGY PROGRESS, Issue 3 2000Gary R. C. Williams A liquid-dispersed reactor equipped with a vertical mesh cylinder for inoculum support was developed for culture of Atropa belladonna hairy roots. The working volume of the culture vessel was 4.4 L with an aspect ratio of 1.7. Medium was dispersed as a spray onto the top of the root bed, and the roots grew radially outward from the central mesh cylinder to the vessel wall. Significant benefits in terms of liquid drainage and reduced interstitial liquid holdup were obtained using a vertical rather than horizontal support structure for the biomass and by operating the reactor with cocurrent air and liquid flow. With root growth, a pattern of spatial heterogeneity developed in the vessel. Higher local biomass densities, lower volumes of interstitial liquid, lower sugar concentrations, and higher root atropine contents were found in the upper sections of the root bed compared with the lower sections, suggesting a greater level of metabolic activity toward the top of the reactor. Although gas-liquid oxygen transfer to the spray droplets was very rapid, there was evidence of significant oxygen limitations in the reactor. Substantial volumes of non-free-draining interstitial liquid accumulated in the root bed. Roots near the bottom of the vessel trapped up to 3,4 times their own weight in liquid, thus eliminating the advantages of improved contact with the gas phase offered by liquid-dispersed culture systems. Local nutrient and product concentrations in the non-free-draining liquid were significantly different from those in the bulk medium, indicating poor liquid mixing within the root bed. Oxygen enrichment of the gas phase improved neither growth nor atropine production, highlighting the greater importance of liquid-solid compared with gas-liquid oxygen transfer resistance. The absence of mechanical or pneumatic agitation and the tendency of the root bed to accumulate liquid and impede drainage were identified as the major limitations to reactor performance. Improved reactor operating strategies and selection or development of root lines offering minimal resistance to liquid flow and low liquid retention characteristics are possible solutions to these problems. [source] Network models for capillary porous media: application to drying technologyCHEMIE-INGENIEUR-TECHNIK (CIT), Issue 6 2010T. Metzger Jun.-Prof. Abstract Network models offer an efficient pore-scale approach to investigate transport in partially saturated porous materials and are particularly suited to study capillarity. Drying is a prime model application since it involves a range of physical effects: capillary pumping, viscous liquid flow, phase transition, vapor diffusion, heat transfer, but also cracks and shrinkage. This review article gives an introduction to this modern technique addressing required model input, sketching important elements of the computational algorithm and commenting on the nature of simulation results. For the case of drying, it is illustrated how network models can help analyze the influence of pore structure on process kinetics and gain a deeper understanding of the role of individual transport phenomena. Finally, a combination of pore network model and discrete element method is presented, extending the application range to mechanical effects caused by capillary forces. [source] Critical evaluation of CFD codes for interfacial simulation of bubble-train flow in a narrow channelINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 6 2007Furkan Özkan Abstract Computational fluid dynamics (CFD) codes that are able to describe in detail the dynamic evolution of the deformable interface in gas,liquid or liquid,liquid flows may be a valuable tool to explore the potential of multi-fluid flow in narrow channels for process intensification. In the present paper, a computational exercise for co-current bubble-train flow in a square vertical mini-channel is performed to investigate the performance of well-known CFD codes for this type of flows. The computations are based on the volume-of-fluid method (VOF) where the transport equation for the liquid volumetric fraction is solved either by the methods involving a geometrical reconstruction of the interface or by the methods that use higher-order difference schemes instead. The codes contributing to the present code-to-code comparison are an in-house code and the commercial CFD packages CFX, FLUENT and STAR-CD. Results are presented for two basic cases. In the first one, the flow is driven by buoyancy only, while in the second case the flow is additionally forced by an external pressure gradient. The results of the code-to-code comparison show that only the VOF method with interface reconstruction leads to physically sound and consistent results, whereas the use of difference schemes for the volume fraction equation shows some deficiencies. Copyright © 2007 John Wiley & Sons, Ltd. [source] CFD simulations of hydrodynamic/thermal coupling phenomena in a bubble column with internalsAICHE JOURNAL, Issue 9 2010Cédric Laborde-Boutet Abstract CFD simulations have been carried out in a full three-dimensional, unsteady, Eulerian framework to simulate hydrodynamic/thermal coupling in a bubble column with internals. A first part of the study, dedicated to the hydrodynamic/thermal coupling in liquid single-phase flows, showed that assuming constant wall temperature on the internals constitutes a reasonable approximation in lieu of comprehensive simulations encompassing shell flow and coolant flow together. A second part dealing with the hydrodynamics of gas,liquid flows in a bubble column with internals showed that a RNG k,, turbulence model formulation accounting for gas-induced turbulence was a relevant choice. The last part used these conclusions to build a hydrodynamic/thermal coupling model of a gas,liquid flow in a bubble column with internals. With a per-phase RNG k,, turbulence model and assuming constant wall temperature, it was possible to simulate heat transfer phenomena consistent with experimentally measured heat transfer coefficients. © 2010 American Institute of Chemical Engineers AIChE J, 2010 [source] A CFD,PBM coupled model for gas,liquid flowsAICHE JOURNAL, Issue 1 2006Tiefeng Wang Abstract A computational fluid dynamics,population balance model (CFD-PBM) coupled model was developed that combines the advantages of CFD to calculate the entire flow field and of the PBM to calculate the local bubble size distribution. Bubble coalescence and breakup were taken into account to determine the evolution of the bubble size. Different bubble breakup and coalescence models were compared. An algorithm was proposed for computing the parameters based on the bubble size distribution, including the drag force, transverse lift force, wall lubrication force, turbulent dispersion force, and bubble-induced turbulence. With the bubble breakup and coalescence models and the interphase force formulations in this work, the CFD-PBM coupled model can give a unified description for both the homogeneous and the heterogeneous regimes. Good agreement was obtained with the experimental results for the gas holdup, liquid velocity, and bubble size distribution. © 2005 American Institute of Chemical Engineers AIChE J, 2006 [source] Measuring Permeability of Rigid Materials by a Beam-Bending Method: I, TheoryJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2000George W. Scherer When a saturated porous material is deformed, pressure gradients are created in the liquid, and the liquid flows within the pores to equilibrate the pressure. This phenomenon can be exploited to measure permeability: A rod of saturated porous material is instantaneously bent by a fixed amount, and the force required to sustain the deflection is measured as a function of time. The force decreases as the liquid flows through the pore network, and the rate of decrease depends on the permeability. This technique has been applied successfully to determine the permeability of gels, as well as their viscoelastic properties; in this paper the method is extended to ceramic materials, such as porous glass and cement paste. The theory has been modified to take account of the compressibility of the solid and liquid phases (whereas, those factors are negligible for gels). Analyses are presented for constant deflection, constant rate of deflection, and sinusoidal oscillation, where the solid phase is either purely elastic or viscoelastic, and the beam is either cylindrical or square. Experimental tests on Vycor® glass and cement paste will be presented in companion papers. [source] | |||||||||||||||||||