Effect Of Flow Conditions Research Articles

NH<sub>4</sub>HS環境での腐食に及ぼす流れの影響

NH<sub>4</sub>HS環境での腐食に及ぼす流れの影響

Effect of flow conditions on spray cone angle of a two-fluid atomizer

A visual study is conducted to determine the effects of operating conditions on the spray cone angle of a two-fluid atomizer. The liquid (water) jets exit from peripheral inclined orifices and are introduced into a high-speed gas (air) stream in the gravitational direction. Using a high-speed imaging system, the spray cone angle is determined for Reynolds numbers ranging from 4×104 to 9×104 and different Weber numbers up to 140. The droplet sizes (Sauter mean diameter) and their distributions are determined using a Malvern Mastersizer X. The results show that the spray cone angle depends on the operating conditions, especially in lower values of Reynolds and Weber numbers. An empirical correlation is also obtained to predict the spray cone angle in terms of these two parameters.

Experimental investigation of porous media combustion in a planar micro-combustor

The micro-combustor (emitter) is a key component of the micro-thermophotovoltaic (TPV) system. In order to improve the system efficiency, higher wall temperature and uniform distribution along the combustor wall is desirable. Porous media combustion of premixed H 2–air in a planar micro-combustor with the channel width of 1 mm is experimentally studied. The wall temperature is measured by using an infrared thermometer under the flow conditions of Ф = 0.6–1.0 and U 0 = 2–3 m/s. The effects of flow conditions and position of the porous media on both the wall temperature distribution and the emitter efficiency are investigated. The experimental results indicate that the wall temperature increases with increasing mixture velocity, and higher emitter efficiency is achieved for mixtures with Ф ≈ 0.8. In addition, the flames are found to be effectively anchored by the inserted porous media, despite the change of flow conditions. The emitter efficiency was noted to be significantly influenced by the position of the porous media, for which the mixture preheating (by the combustor wall) is believed to be a main reason.

Chromatographic partitioning of impurities (H 2S) contained in a CO 2 stream injected into a deep saline aquifer: Part 2. Effects of flow conditions

Laboratory experiments reported in a companion paper were carried out to examine the chromatographic partitioning of impurities contained in a stream of CO 2 injected into a deep saline aquifer. The solubility of the impurity gas in the CO 2 stream compared to that of CO 2, the in situ conditions of pressure, temperature and water salinity, and the concentration of the impurity gas affect the partitioning of the two gases. For CO 2 streams containing H 2S, numerical simulations reported here have successfully replicated the laboratory results including the breakthrough of CO 2 ahead of H 2S. Sensitivity analysis performed with the numerical model has shown that flow conditions, controlled by such parameters as medium permeability, pressure gradient, dispersion, gas mobility and flow direction, affect the breakthrough time and separation of the two gases, leading to delayed or earlier breakthrough, and increasing or decreasing the time lag between the breakthrough of the two gases. Vertical bottom-up flow leads to earlier breakthrough, while top-down flow leads to delayed breakthrough. These results are important in establishing monitoring strategies at CO 2 storage sites and in evaluating the risks associated with the possible leakage of injected CO 2 that contains impurities.

Modeling cell interactions under flow

In this review, we summarize the current state of understanding of the processes by which leukocytes, and other cells, such as tumor cells interact with the endothelium under various blood flow conditions. It is shown that the interactions are influenced by cell-cell adhesion properties, shear stresses due to the flow field and can also be modified by the cells microrheological properties. Different adhesion proteins are known to be involved leading to particular mechanisms by which interactions take place during inflammation or metastasis. Cell rolling, spreading, migration are discussed, as well as the effect of flow conditions on these mechanisms, including microfluidic effects. Several mathematical models proposed in recent years capturing the essential features of such interaction mechanisms are reviewed. Finally, we present a recent model in which the adhesion is given by a kinetics theory based model and the cell itself is modeled as a viscoelastic drop. Qualitative agreement is found between the predictions of this model and in vitro experiments.

Simulation of growth rate and deposition profile on the periodically patterned substrate

The growth of GaN on the patterned substances has proven favorable to achieve thick, crack-free GaN layers. Based on these methods, we specially designed periodically patterned Si substrate process, which is referred to as lateral epitaxy on patterned Si substrate (LEPS). High crystalline quality GaN are obtained by using this technique. In this paper, numerical modeling of transport and reaction of species is performed to estimate the growth rate of GaN from the reaction of trimethyl gallium (TMG) and ammonia. The effect of fabricated structure of feature scale model will be predicted by using the topography simulator, and deposition profile of the GaN on the pattern will be discussed. The effect of flow conditions and pattern shape and periodicity will also be addressed, which can be critical for the quality of crystal growth. The dependency of step coverage and conformality of patterned mask will also be discussed.

Three-Dimensional Simulations of Reactive Gas Uptake in Single Airway Bifurcations

The pattern of lung injury induced by the inhalation of ozone (O(3)) depends on the dose delivered to different tissues in the airways. This study examined the distribution of O(3) uptake in a single, symmetrically branched airway bifurcation. Reaction in the epithelial lining fluid was assumed to be so rapid that O(3) concentration was negligible along the entire surface of the bifurcation wall. Three-dimensional numerical solutions of the continuity, Navier-Stokes and convection-diffusion equations were obtained for steady inspiratory and expiratory flows at Reynolds numbers ranging from 100 to 500. The total rate of O(3) uptake was found to increase with increasing flow rate during both inspiration and expiration. Hot spots of O(3) flux appeared at the carina of the bifurcation for virtually all inspiratory and expiratory Reynolds numbers considered in the simulations. At the lowest expiratory Reynolds number, however, the location of the maximum flux was shifted to the outer wall of the daughter branch. For expiratory flow, additional hot spots of flux were found on the parent branch wall just downstream of the branching region. In all cases, O(3) uptake in the single bifurcation was larger than that in a straight tube of equal inlet radius and wall surface area. This study provides insight into the effect of flow conditions on O(3) uptake and dose distribution in individual bifurcations.

Thermal stability of shear‐induced precursor structures in isotactic polypropylene by rheo‐X‐ray techniques with couette flow geometry

AbstractCombined in situ rheo‐SAXS (small‐angle X‐ray scattering) and ‐WAXD (wide‐angle X‐ray diffraction) studies using couette flow geometry were carried out to probe thermal stabilty of shear‐induced oriented precursor structure in isotactic polypropylene (iPP) at around its normal melting point (162 °C). Although SAXS results corroborated the emerging consensus about the formation of “long‐living” metastable mesomorphic precursor structures in sheared iPP melts, these are the first quantitative measures of the limiting temperature at which no oriented structures survive. At the applied shear, rate = 60 s−1 and duration ts = 5 s, the oriented iPP structures survived a temperature of 185 °C for 1 h after shear, while no stable structures were detected at and above 195 °C. Following Keller's concepts of chain orientation in flow, it is proposed that the chains with highly oriented high molecular weight fraction are primarily responsible for their stability at high temperatures. Furthermore, the effects of flow condition, specifically the shear temperature, on the distributions of oriented and unoriented crystals were determined from rheo‐WAXD results. As expected, at a constant flow intensity (i.e., rate = 30 s−1 and duration, ts = 5 s), the oriented crystal fraction decreased with the increase in temperature above 155 °C, below which the oriented fraction decreased with the decrease in temperature. As a result, a crystallinty “phase” diagram, i.e., temperature versus crystal fraction ratio, exhibited a peculiar “hourglass” shape, similar to that found in many two‐phase polymer–polymer blends. This can be explained by the competition between the oriented and unoriented crystals in the available crystallizable species. Below the shear temperature (155 °C), the unoriented crystals crystallized so rapidly that they overwhelmed the crystallization of the oriented crystals, thus depleting a major portion of the crystallizable species and increasing their contribution in the final total crystalline phase. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3553–3570, 2006

Negative wake generation of FENE-CR fluids in uniform and Poiseuille flows past a cylinder

The effect of flow conditions on the “negative wake” generation (longitudinal velocity overshoot behind a cylinder in the viscoelastic fluid flow along the centerline) has been investigated. FENE-CR model that predicts constant shear viscosity and controlled extensional viscosity was considered as a constitutive equation. The discrete elastic viscous split stress-G/streamline upwind Petrov–Galerkin (DEVSS-G/SUPG) formulation was employed and the high-resolution solutions were obtained with an efficient iterative solver based on the incomplete LU(0)-type preconditioner and BiCGSTAB. We found that the “negative wake” generation was more obvious in uniform flow conditions than in Poiseuille flow, which suggests that the experimentally unrevealed “negative wake” generation of Boger fluids could be partially attributed to the geometrical effect of Poiseuille flow. The “negative wake” generation was more discernable at low extensibility and high value of viscosity ratio, which agrees well with the previous studies. In addition, we could observe an undershoot phenomenon in Poisseuille flow condition, which has never been reported.

Un dispositif d'écoulement pour l'étude des réactions cellulaires au contact d'une paroi poreuse

Biomaterials used in biomedical devices, such as bioartificial organs, hemodialysers and vascular prosthesis, are porous and are exposed to normal and tangential flow of physiological fluid. Flow induced forces may influence the responses (morphology, migration, detachment) of cells adhering to a porous wall. In classical in-vitro flow devices, cells are submitted to only tangential stresses. We designed a new flow system in order to take into account the influence of a transmural pressure. It is a parallel-plate flow chamber with a porous bottom wall (biomaterial). We report an application of this system to study the effect of flow conditions on cells adhering to a dialysis membrane. The mechanically induced cell shape changes are correlated to biochemical analysis (activation of the cAMP pathway).

Operating Characteristics and Performance of a Monolithic Downflow Bubble Column Reactor in Selective Hydrogenation of Butyne‐1,4‐diol

AbstractThe effects of flow condition, bubble dispersion level, and liquid flow rate on the behavior of a novel monolithic downflow bubble column (M‐DBC) were investigated using a reaction model, the palladium‐catalyzed hydrogenation of butyne‐1,4‐diol. The stable and closely packed homogeneous bubble dispersion present in the bulk region of the M‐DBC allowed effective introduction of the gas‐liquid phase for formation of Taylor flow inside the monolith channels. The condition defined as the minimum level dispersion was required in order to obtain high selectivity towards the intermediate product, cis‐2‐butene‐1,4‐diol. Enhanced reaction rates were obtained at increasing the dispersion level and lowering the liquid flow rate. Comparison with the DBC employing 5 % Pd/C powder catalyst and 1 % Pd‐on‐Raschig‐ring revealed a better performance of the M‐DBC (1 % Pd loading) with the advantage of smaller reaction volume and intensified reaction rate. As an alternative to conventional three‐phase reactors, the M‐DBC was so simple due to its inherent characteristic operation and no specially designed device is required.

Effect of Internal Coolant Crossflow on the Effectiveness of Shaped Film-Cooling Holes

Film-cooling was the subject of numerous studies during the past decades. However, the effect of flow conditions on the entry side of the film-cooling hole on film-cooling performance has surprisingly not received much attention. A stagnant plenum which is widely used in experimental and numerical studies to feed the holes is not necessarily a right means to re-present real engine conditions. For this reason, the present paper reports on an experimental study investigating the effect of a coolant crossflow feeding the holes that is oriented perpendicular to the hot gas flow direction to model a flow situation that is, for instance, of common use in modern turbine blades’ cooling schemes. A comprehensive set of experiments was performed to evaluate the effect of perpendicular coolant supply direction on film-cooling effectiveness over a wide range of blowing ratios (M=0.5…2.0) and coolant crossflow Mach numbers Mac=0…0.6. The coolant-to-hot gas density ratio, however, was kept constant at 1.85 which can be assumed to be representative for typical gas turbine applications. Three different hole geometries, including a cylindrical hole as well as two holes with expanded exits, were considered. Particularly, two-dimensional distributions of local film-cooling effectiveness acquired by means of an infrared camera system were used to give detailed insight into the governing flow phenomena. The results of the present investigation show that there is a profound effect of how the coolant is supplied to the hole on the film-cooling performance in the near hole region. Therefore, crossflow at the hole entry side has be taken into account when modeling film-cooling schemes of turbine bladings.

Solidification behavior of Sn-15 wt pct Pb alloy under a high shear rate and high intensity of turbulence during semisolid processing

Microstructural evolution under intensive forced convection is of importance to the development of new semisolid processing technologies. Although efforts have been made to understand the nucleation and growth behavior of the primary phase under forced convection, important aspects of microstructural evolution still remain as open questions. Experimental work was undertaken to investigate the effects of a high shear rate and high intensity of turbulence on the solidification behavior of a Sn-15 wt pct Pb alloy using a twin-screw extruder. It was found that increasing the shear rate and intensity of turbulence can give rise to substantial grain refinement, which can be attributed to the increased effective nucleation rate caused by the extremely uniform temperature and composition fields in the bulk liquid at early stages of solidification. It was also found that forced convection increases the growth velocity and stabilizes the solidification interface, resulting in a transition of the growth morphology from rosette to spheroid with increasing shear rate and intensity of turbulence. Discussions are made on the effects of flow conditions on the nucleation behavior, constitutional undercooling, stability of the solidification interface, and growth morphology.

214 微粉体のプラグ輸送におけるプラグ性状が圧力損失に及ぼす影響

214 微粉体のプラグ輸送におけるプラグ性状が圧力損失に及ぼす影響

Numerical study of the evaporative cooling of liquid film in laminar mixed convection tube flows

A numerical study is reported to investigate the evaporative cooling of liquid film falling along a vertical tube. A marching procedure is employed for solution of the equation of mass momentum, energy and concentration in the flow. Numerical results for air-water system are presented. The effects of flow conditions on the film cooling mechanism are discussed. Results show that a better liquid film cooling is noticed for a system having a higher inlet liquid temperature T L0, a higher gas flow Reynolds number Re or a lower liquid flow rate Γ 0. Additionally, the results indicate that the convection of heat by the flowing water film becomes the main mechanism for heat removal from the interface.

The effect of air swirl profile on the instability of a viscous liquid jet

A temporal linear stability analysis has been carried out to predict the instability of a viscous liquid jet surrounded by a swirling air stream with three-dimensional disturbances. The effects of flow conditions and fluid properties on the instability of the liquid jet are investigated via a parametric study by varying axial Weber number axial velocity ratio of the gas to liquid phase, swirl Weber numbers, density ratio and the Ohnesorge number. It is observed that the relative axial velocity between the liquid and gas phases promotes the interfacial instability. As the axial Weber number increases, the growth rates of unstable waves, the most unstable wavenumber and the unstable range of wavenumbers increase. Meanwhile, the increasing importance of helical modes compared to the axisymmetric mode switches the breakup regime from the Rayleigh regime to the first wind-induced regime and on to the second wind-induced regime. The predicted range of wavenumbers in which the first helical mode has higher growth rates than the axisymmetric mode agrees very well with experimental data. Results show that the destabilizing effects of the density ratio and the axial Weber number are nearly the same. Liquid viscosity inhibits the disintegration process of the liquid jet by reducing the growth rate of disturbances and by shifting the most unstable wavenumber to a lower value. Moreover, it damps higher helical modes more significantly than the axisymmetric mode. Air swirl has a stabilizing effect on the liquid jet. As air swirl strength increases, the growth rates of helical modes are reduced more significantly than that of the axisymmetric mode. The air swirl profile is found to have a significant effect on the instability of the liquid jet. The global, as well as local, effects of the swirl profile are examined in detail.

Instability of an Annular Liquid Sheet Surrounded by Swirling Airstreams

A theoretical model to predict the instability of an annular liquid sheet subjected to coaxial swirling airstreams is developed. The model incorporates essential features of a liquid sheet downstream of a prefilming airblast atomizer such as three-dimensional disturbances, inner and outer air swirl, finite film thickness, and finite surface curvature. Effects of flow conditions, fluid properties, and film geometry on the instability of the liquid sheet are investigated. It is observed that the relative axial velocity between the liquid and the gas phases enhances the interfacial aerodynamic instability by increasing the growth rate and the most unstable wave number. At low velocities, a combination of inner and outer airstreams is more effective in disintegrating the liquid sheet than only the inner or only the outer airstream. Also, the inner air is more effective than the outer air in promoting disintegration. Swirl not only increases the growth rate and the range of unstable wave numbers but also shifts the dominant mode from the axisymmetric mode to a helical mode. With the presence of air swirl, the most unstable wave number and the maximum growth rate are higher than their no-swirl counterparts

Electrically Conductive Extruded Filaments of Polyaniline/Polymer Blends

Blends of plasticized polystyrene and conductive polyaniline (PANI) were prepared by melt processing, and extruded filaments were obtained by using a capillary rheometer. The effect of flow conditions, including temperature and shear rate, on the morphology of the blends and on the resulting electrical conductivity were investigated. Under a combination of specific processing and given blend compositions, the electrical conductivity was found to be independent of shear level over a wide range of shear rates. Thus, conductive melt processible PANI-based blends can be designed, however relatively high PANI concentrations (well above percolation) are required. Blend systems can be developed to further reduce the PANI concentration in ternary component blends.

In vitro platelet adhesion to endothelial cells at low shear rates during copper deficiency in rats

Dietary copper restriction impairs thrombogenesis and hemostasis in rat microcirculation. In this study, the role of wall shear rate in platelet-to-endothelial cell adhesion in vitro was studied during copper deficiency. Platelets were obtained from male, weanling Sprague-Dawley rats fed purified diets, which were either copper-adequate (CuA, 6.3 μg Cu/g) or copper-deficient (CuD, 0.3 μg Cu/g), for 4 weeks. Platelets were through a parallel plate flow chamber containing cultured rat endothelial cells which were either normal or treated with the copper chelator tetraethylenepentamine (TEPA). Since platelet von Willebrand factor (vWF) concentration is decreased in CuD rats, we determined the platelet adhesion when CuD platelets were incubated in purified vWF (0.2 units/ml). Adhesion to normal endothelial cells was significantly lower for CuD platelets vs. CuA platelets at low (70 s−1; 21.5 ± 4.0% vs. 37.0 ± 2.7%) and relatively high (200 s−1; 9.3 ± 1.7% vs. 19.5 ± 1.1%) wall shear rates. Adhesion of CuD platelets to normal endothelial cells incubated in vWF was not different from adhesion of CuA platelets. Adhesion to TEPA-treated endothelial cells was lower than adhesion to normal endothelial cells for both CuA and CuD platelets (30.6 ± 1.5% vs. 37 ± 2.7%). Although increasing the shear rate (from 70 s−1 to 200 s−1) decreased adhesion of both CuA and CuD platelets, the ratio between groups remained similar. These results demonstrate that adhesion of CuD platelets to normal endothelial cells is less than that of CuA platelets under flow conditions typical for venules. Further, altered shear rate does not account for the depressed in vitro platelet adhesion. Thus, alteration of platelet and endothelial cell properties by copper deficiency may be of greater importance than the effect of flow conditions on endothelial cells in delaying thrombosis. J. Trace Elem. Exp. Med. 12:25–36, 1999. Published 1999 Wiley-Liss, Inc.

A Modified Water Quality Model for P. Redicting BOD and DO Variations in a Shallow Polluted Channel

This study developed a new water quality model by taking into consideration the effects of flow conditions and biofilm metabolism on the BOD and DO changes in a shallow polluted channel. Experimental tests were performed in a model channel under various flow conditions. The test results showed that the organic matter deoxygenation rate coefficient (k1) varies significantly with the water velocities instead of being a constant as previously believed. The influences of organic concentration on the deoxygenation rate of biofilms was found to decrease with an increase in the Reynolds number. The present model along with a simplified version and the conventional Streeter-Phelps model were utilized to compare of experimental data obtained from test runs under various flow conditions. The test results revealed that the residual BOD and DO concentrations predicted by the present study agree very well with the measured values while the predicted values using the two other models deviate significantly from the observed data.