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Flow Distribution (flow + distribution)
Selected AbstractsArterial structural and functional alterations in uraemiaEUROPEAN JOURNAL OF CLINICAL INVESTIGATION, Issue 2005A. P. Guérin Abstract Epidemiological and clinical studies have shown that cardiovascular disease in patients with end-stage renal disease (ESRD) is frequently related to damage of large conduit arteries. Arterial disease is responsible for the high incidence of ischaemic heart disease, peripheral artery diseases, left ventricular hypertrophy and congestive heart failure. The vascular complications in ESRD are ascribed to two different but associated mechanisms, namely atherosclerosis and arteriosclerosis. Whereas the former principally affects the conduit function with ischaemic lesions being the most characteristic consequence, the latter primarily disturbs the dampening function of large arteries. Arteriosclerosis in ESRD patients is characterized by diffuse dilation and wall hypertrophy of large conduit arteries and stiffening of arterial walls. These changes represent a clinical form of an accelerated ageing process. The main clinical characteristics due to arterial stiffening are isolated increase in systolic blood pressure with normal or lower diastolic pressure resulting in an increased pulse pressure. The consequences of these alterations are: (i) an increased left ventricular afterload with development of left ventricular hypertrophy and increased myocardial oxygen demand; and (ii) altered coronary perfusion and subendocardial blood flow distribution. Epidemiological studies have identified arterial remodelling and stiffening as independent predictors of overall and cardiac mortality in ESRD patients. [source] The combined effects of non-planarity and asymmetry on primary and secondary flows in the small bronchial tubesINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 2 2009B. Soni Abstract The laminar flow in the small bronchial tubes is quite complex due to the presence of vortex-dominated, secondary flows. In this paper, we report the results of a numerical investigation of the simultaneous effects of asymmetric and non-planar branching on the primary and secondary flows in the small bronchial tubes, i.e. generations 6,12. We simulate steady-state inspiratory flow at a Reynolds number of 1000 in three-generation, asymmetric planar and non-planar bronchial tube models. The non-planar model was defined by applying a 90° out-of-plane rotation to the third-generation branches. A detailed mesh refinement study was performed in order to demonstrate mesh independence. Significant differences were observed between flows in the planar and non-planar models. An uneven mass flow distribution was observed in the non-planar model in contrast to the evenly distributed mass flow in the planar model. The secondary flows created symmetric vortex patterns in the planar model, whereas vortex symmetry was lost in the non-planar model. These results illustrate the importance of incorporating asymmetry in addition to non-planarity in the geometric models. Copyright © 2008 John Wiley & Sons, Ltd. [source] Investigation of coolant flow distribution and the effects of cavitation on water pump performance in an automotive cooling systemINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 3 2009Kibum Kim Abstract Cavitation is a well-known phenomenon that causes performance losses in all kinds of hydraulic machinery, including automotive water pumps. The present study uses a coolant flow test rig to investigate cavitation in water pumps. The coolant flow rate was measured for various coolant temperatures and compositions. This study validates that cavitation occurs during the coolant warm-up period, in which coolant temperature is typically below 80°C. Cavitation was also related to a drop in the water pump inlet pressure and driving torque. Based on the results from this study, it can be concluded that cavitation is affected by coolant temperature, engine speed, and coolant composition. Furthermore, it is found that the use of an electric water pump is effective for minimizing the pressure drop and driving loss of the pump. Copyright © 2008 John Wiley & Sons, Ltd. [source] The effect of condenser heat transfer on the energy performance of a plate heat pipe solar collectorINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 10 2005Jorge Facão Abstract For a novel prototype solar collector, using a plate heat pipe, condenser heat transfer was analysed in detail. The condenser has the shape of a rectangular channel. Flow and heat transfer of water in the rectangular channel was modelled and the heat transfer coefficient assessed, using the Fluent code. Under typical operating conditions a mixed convection situation occurs. The channel is inclined and heating is through one wall only (upper channel surface). The range of temperature differences considered was similar to the one verified under real operating conditions, covering a wide range of Grashof numbers. Results showed that the Nusselt number is significantly higher than the one for forced convection in a rectangular channel with fully developed boundary layers. In order to enhance heat transfer, a modification to the rectangular channel was analysed, using baffles to improve flow distribution and increase velocity. The effect of this modification on collector energy performance (efficiency) was assessed. Copyright © 2005 John Wiley & Sons, Ltd. [source] Dopamine increases renal oxygenation: a clinical study in post-cardiac surgery patientsACTA ANAESTHESIOLOGICA SCANDINAVICA, Issue 2 2010BENGT REDFORS Background: Imbalance of the renal medullary oxygen supply/demand relationship can cause ischaemic acute renal failure (ARF). The use of dopamine for prevention/treatment of ischaemic ARF has been questioned. It has been suggested that dopamine may increase renal oxygen consumption (RVO2) due to increased solute delivery to tubular cells, which may jeopardise renal oxygenation. Information on the effects of dopamine on renal perfusion, filtration and oxygenation in man is, however, lacking. We evaluated the effects of dopamine on renal blood flow (RBF), glomerular filtration rate (GFR), RVO2 and renal O2 demand/supply relationship, i.e. renal oxygen extraction (RO2Ex). Methods: Twelve uncomplicated, mechanically ventilated and sedated post-cardiac surgery patients with pre-operatively normal renal function were studied. Dopamine was sequentially infused at 2 and 4 ug/kg/min. Systemic haemodynamics were evaluated by a pulmonary artery catheter. Absolute RBF was measured using two independent techniques: by the renal vein thermodilution technique and by infusion clearance of paraaminohippuric acid (PAH), with a correction for renal extraction of PAH. The filtration fraction (FF) was measured by the renal extraction of 51Cr-EDTA. Results: Neither GFR, tubular sodium reabsorption nor RVO2 was affected by dopamine, which increased RBF (45,55%) with both methods, decreased renal vascular resistance (30,35%), FF (21,26%) and RO2Ex (28,34%). The RBF/CI ratio increased with dopamine. Dopamine decreased renal PAH extraction, suggestive of a flow distribution to the medulla. Conclusions: In post-cardiac surgery patients, dopamine increases the renal oxygenation by a pronounced renal pre-and post-glomerular vasodilation with no increases in GFR, tubular sodium reabsorption or renal oxygen consumption. [source] Gas-solid flow distribution through identical vertical passages: Modeling and stability analysisAICHE JOURNAL, Issue 8 2010Mohammad S. Masnadi Abstract As previous evidence shows, the distribution of gas-solid flow traveling through identical parallel paths can be significantly nonuniform, often with harmful operating consequences in practice. A fundamental analytical and numerical study is performed on the distribution of gas-solid pneumatic flow passing through a "Y branch". While many steady-state gas-solid distribution solutions, including a uniform distribution, satisfy the governing equations, linear stability analysis indicates that the uniform distribution is stable the most likely solution of the system. Both 2-D (two-dimensional) and 3-D multiphase computational fluid dynamic simulations and stability analyses confirm the analytical conclusions. © 2010 American Institute of Chemical Engineers AIChE J, 2010 [source] Flow distribution and mass transfer in a parallel microchannel contactor integrated with constructal distributorsAICHE JOURNAL, Issue 2 2010Jun Yue Abstract Flow distribution and mass transfer characteristics during CO2 -water flow through a parallel microchannel contactor integrated with two constructal distributors have been investigated numerically and experimentally. Each distributor comprises a dichotomic tree structure that feeds 16 microchannels with hydraulic diameters of 667 ,m. It was found that constructal distributors could ensure a nearly uniform gas,liquid distribution at high gas flow rates where the ideal flow pattern was slug-annular flow. Nevertheless, at small gas flow rates where the ideal flow pattern was slug flow, a significant flow maldistribution occurred primarily due to the lack of large pressure barrier inside each distributor, indicating that dynamic pressure fluctuation in parallel microchannels greatly disturbed an otherwise good flow distribution therein. It was further shown that the present parallel microchannel contactor could realize the desired mass transfer performance previously achieved in one single microchannel under relatively wide operational ranges due to the integration of constructal distributors. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Proximal pulmonary artery blood flow characteristics in healthy subjects measured in an upright posture using MRI: The effects of exercise and age,JOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 6 2005Christopher P. Cheng PhD Abstract Purpose To use MRI to quantify blood flow conditions in the proximal pulmonary arteries of healthy children and adults at rest and during exercise in an upright posture. Materials and Methods Cine phase-contrast MRI was used to calculate mean flow and reverse flow index (RFI) in the main (MPA), right (RPA), and left (LPA) pulmonary arteries in healthy children and adults in an open-MRI magnet equipped with an upright MRI-compatible ergometer. Results From rest to exercise (150% resting heart rate), blood flow (liters/minute/m2) increased in the RPA (1.4 ± 0.3 vs. 2.5 ± 0.4; P < 0.001), LPA (1.1 ± 0.3 vs. 2.2 ± 0.6; P < 0.001), and MPA (2.7 ± 0.5 vs. 4.9 ± 0.5; P < 0.001). RFI decreased in the LPA (0.040 ± 0.030 vs. 0.017 ± 0.018; P < 0.02) and MPA (0.025 ± 0.024 vs. 0.008 ± 0.007; P < 0.03). Adults experienced greater retrograde flow in the MPA than the children (0.042 ± 0.029 vs. 0.014 ± 0.012; P < 0.02). Conclusion It appears that at both rest and during exercise, in children and adults alike, RPA/LPA mean blood flow distribution is predominantly determined by distal vascular resistance, while retrograde flow is affected by proximal pulmonary bifurcation geometry. J. Magn. Reson. Imaging 2005;21:752,758. © 2005 Wiley-Liss, Inc. [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] Real-Time Contrast Imaging: A New Method to Monitor Capillary Recruitment in Human Forearm Skeletal MuscleMICROCIRCULATION, Issue 3 2008Alexandra H. Mulder ABSTRACT Objective: Muscle capillary perfusion can be measured by contrast-enhanced ultrasound. We examined whether a less time-consuming ultrasound technique, called "real-time imaging," could be used to measure capillary recruitment in human forearm skeletal muscle. Methods: We measured microvascular blood volume and microvascular flow velocity using bolus injections of contrast microbubbles after forearm muscle exercise and a two-hour infusion of insulin into the brachial artery (both associated with capillary recruitment) and after sodium nitroprusside infusion (no changes in flow distribution). Results: After an intravenous bolus injection of the contrast agent, the steady-state concentration of contrast agent in forearm muscle lasted long enough (approximately 190 seconds) for the duration of the measurements (which take 70,80 seconds), rendering the continuous infusion of microbubbles unnecessary. Microvascular blood-volume measurements showed a good short-time reproducibility and a good reproducibility after repositioning of the forearm. Reproducibility of microvascular flow velocity was too low. Exercise and insulin infusion both increased microvascular blood volume, consistent with capillary recruitment. Sodium nitroprusside had no effect. Conclusion: Real-time contrast imaging, after bolus injections of an ultrasound contrast agent, provides reliable information about capillary recruitment in human forearm skeletal muscle, and may offer a valuable tool in studying human (patho)physiology. [source] The influence of power-law rheology on flow distribution in coathanger manifolds,POLYMER ENGINEERING & SCIENCE, Issue 3 2003J. D. Reid Coathanger dies are effective in delivering uniform flow if a polymer melt; however, when the fluid flow index varies from the design values, the flow is not uniform. Although mechanisms such as die lip adjustments have been effective tools for adjusting flow profiles, the issue of a variable flow index has not been fully addressed at the design stage. An analytical solution, based on the assumptions present in the 1-D design equation, has been developed for the flow distribution in a coathanger manifold. This solution determines the flow distribution for a power-law fluid with a flow index n* in a manifold designed for a separate flow index n*. From this solution, a uniformity index and a critical design angle are defined. The critical design angle is the angle at which the local derivative of the uniformity index with respect to n* approaches a maximum (for n* < n) or a minimum (for n* > n) as a function of the design angle. The critical design angle is independent of n and is presented as a function of the manifold aspect ratio. [source] Design Considerations for Plate and Frame Ultrafiltration Modules by Computational Fluid Dynamics Analysis,THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2006Mauro M. Dal-Cin Abstract Pressure and flow maldistributions were studied in a full-scale industrial plate and frame ultrafiltration module, operating in a Z flow pattern, for the recovery of used motor oils. Solutions were obtained using (1) a three-dimensional solution of the Navier-Stokes equation using computational fluid dynamics and (2) Bernoulli's equation and a momentum balance in one dimension. Fluid decelerations and accelerations generated pressure increases and decreases in the distributor and collector, respectively, biasing the flow distribution to the last channel. Several modifications to the original design were evaluated; the most effective was larger distributor and collector diameters, which greatly improved the uniformity of the flow distribution and transmembrane pressure, and reduced the overall pressure drop in a bank. A variable diameter distributor and collector module was designed using the 1-D model. Flow distribution was significantly improved but also yielded an undesirable overall higher pressure drop and a pressure maldistribution in the bank. The maldistribution of the main inlet manifold to the distributors in the first bank was strongly dependent on the module design. The flow distribution across the width of a channel became uniform within a short distance, essentially eliminating the need to consider this design aspect any further. Flows at the bank outlets, and hence inlets of the following bank, showed uniform lateral distribution in all cases, suggesting that future modelling work can be limited to a fraction of the module width, based on symmetry, in order to gain computational efficiency. On a étudié les mauvaises distributions de pression et d'écoulement dans un module d'ultrafiltration à plateaux et à cadres à l'échelle industrielle, fonctionnant dans un schéma d'écoulement en Z, pour la récupération des huiles de moteurs usées. Des solutions ont été obtenues avec (1) une solution tridimensionnelle de l'équation de Navier-Stokes utilisant la mécanique des fluides par ordinateur, et (2) l'équation de Bernoulli et un bilan de quantité de mouvement unidimensionnel. Les décélérations et accélérations de fluide entraînent des augmentations et diminutions de pression dans le distributeur et le collecteur, respectivement, ce qui fausse la distribution d'écoulement dans le dernier canal. On a évalué plusieurs modifications du concept original; la plus efficace sont des diamètres de distributeur et de collecteur plus larges, qui permettent d'améliorer grandement l'uniformité de la distribution d'écoulement et la pression transmembranaire, et qui réduisent la perte de charge globale dans une batterie. Un module de distributeur et de collecteur de diamètres variables a été conçu au moyen du modèle 1D. La distribution d'écoulement est significativement améliorée mais cause une perte de charge globale plus grande indésirable et une mauvaise distribution de pression dans la batterie. La mauvaise distribution du manifold d'entrée principal vers les distributeurs dans la première batterie est fortement dépendante de la conception du module. La distribution d'écoulement dans toute la largeur d'un canal devient uniforme sur une courte distance, éliminant essentiellement le besoin d'approfondir cet aspect de la conception. L'écoulement en sortie de batteries et donc à l'entrée des batteries suivantes montre une distribution latérale uniforme dans tous les cas, ce qui suggère que le travail de modélisation futur peut se limiter à une fraction de la largeur du module, pour des raisons de symétrie, pour gagner de l'efficacité numérique. [source] Experimental studies of liquid flow maldistribution in a random packed columnTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2000Fuhe Yin Abstract Liquid flow distribution has been a major concern when scaling up random packed columns. This study concerns the measurements of liquid flow distribution in a large scale column packed with 25.4 mm stainless steel Pall rings. The liquid flow distribution was studied with packed bed height from 0.9 to 3.5 m, liquid flow rate from 2.91 to 6.66 kg/m2·s, and gas flow rate from 0 to 3.0 kg/m2·s. In addition, three systems, water/air, aqueous detergent solution/air and Isopar/air, were used to study the effect of liquid physical properties on liquid flow distribution, and two different liquid distributors were employed to test the effect of liquid distributor design. It was found that liquid flow distribution was strongly influenced by liquid distributor design, packed bed height, gas flow rate and liquid viscosity, slightly influenced by liquid flow rate, but not by liquid surface tension. La distribution de l'écoulement liquide pose un problème important pour la mise à l'échelle des colonnes garnies aléatoirement. Cette étude porte sur des mesures de distribution d'écoulement liquide dans une colonne de grande échelle garnie d'anneaux Pall en acier inoxydable de 25,4 mm de diamètre. La distribution de l'écoulement liquide a été étudiée pour une hauteur de lit garni entre 0,9 et 3,5 m, un débit liquide entre 2,91 et 6,66 kg/m2·s et un débit de gaz entre 0 et 3,0 kg/m2·s. En outre, on a eu recours à trois systèmes, soient eau/air, solution à base de détergent aqueuse/air et Isopar/air, pour étudier l'effet des propriétés physiques du liquide sur la distribution de l'écoulement liquide, et deux distributeurs de liquide différents ont été utilisés afin de tester l'effet de la conception du distributeur de liquide. On a trouvé que la distribution de l'écoulement liquide était fortement influenceé par la conception du distributeur de liquide, la hauteur de lit garni, le débit de gaz et la viscosité du liquide, était peu influencée par le débit du liquide, et n'était pas influencée par la tension de surface du liquide. [source] Flow Distribution During Cardiopulmonary Bypass in Dependency on the Outflow Cannula PositioningARTIFICIAL ORGANS, Issue 11 2009Tim A.S. Kaufmann Abstract Oxygen deficiency in the right brain is a common problem during cardiopulmonary bypass (CPB). This is linked to an insufficient perfusion of the carotid and vertebral artery. The flow to these vessels is strongly influenced by the outflow cannula position, which is traditionally located in the ascending aorta. Another approach however is to return blood via the right subclavian artery. A computational fluid dynamics (CFD) study was performed for both methods and validated by particle image velocimetry (PIV). A 3-dimensional computer aided design model of the cardiovascular (CV) system was generated from realtime computed tomography and magnetic resonance imaging data. Mesh generation (CFD) and rapid prototyping (PIV) were used for the further model creation. The simulations were performed assuming usual CPB conditions, and the same boundary conditions were applied for the PIV validation. The flow distribution was analyzed for 55 cannula positions inside the aorta and in relation to the distance between the cannula tip and the vertebral artery branch for subclavian cannulation. The study reveals that the Venturi effect due to the cannula jet appears to be the main reason for the loss in cerebral perfusion seen clinically. It provides a PIV-validated CFD method of analyzing the flow distribution in the CV system and can be transferred to other applications. [source] The Impact of Aortic/Subclavian Outflow Cannulation for Cardiopulmonary Bypass and Cardiac Support: A Computational Fluid Dynamics StudyARTIFICIAL ORGANS, Issue 9 2009Tim A.S. Kaufmann Abstract Approximately 100 000 cases of oxygen deficiency in the brain occur during cardiopulmonary bypass (CPB) procedures each year. In particular, perfusion of the carotid and vertebral arteries is affected. The position of the outflow cannula influences the blood flow to the cardiovascular system and thus end organ perfusion. Traditionally, the cannula returns blood into the ascending aorta. But some surgeons prefer cannulation to the right subclavian artery. A computational fluid dynamics study was initially undertaken for both approaches. The vessel model was created from real computed tomography/magnetic resonance imaging data of young healthy patients. The simulations were run with usual CPB conditions. The flow distribution for different cannula positions in the aorta was studied, as well as the impact of the cannula tip distance to vertebral artery for the subclavian position. The study presents a fast method of analyzing the flow distribution in the cardiovascular system, and can be adapted for other applications such as ventricular assist device support. It revealed that two effects cause the loss of perfusion seen clinically: a vortex under the brachiocephalic trunk and low pressure regions near the cannula jet. The results suggest that cannulation to the subclavian artery is preferred if the cannula tip is sufficiently far away from the branch of the vertebral artery. For the aortic positions, however, the cannula should be injected from the left body side. [source] Experimentelle Bestimmung der hygrischen Sorptionsisotherme und des Feuchtetransportes unter instationären BedingungenBAUPHYSIK, Issue 2 2006Assistent und Laborleiter Rudolf Plagge Dr.-Ing. Mit der vorgestellten Augenblicksprofil-Methode (APM) werden sowohl die relative Luftfeuchte und die Temperatur, als auch der volumetrische Wassergehalt in bestimmten Positionen in einem porösen Material bestimmt. Die Messungen werden kontinuierlich unter instationären Bedingungen durchgeführt. Damit erlaubt die APM eine dynamische und gleichzeitige Messung der hygroskopischen Sorptionsisotherme und der hygrischen Feuchteleitfähigkeit für einzelne Kompartimente innerhalb der Materialprobe. Die Feuchteleitfähigkeit wird aus den sich zeitlich ändernden Potentialgradienten und den dazugehörigen Feuchteverteilungen für die jeweiligen Kompartimente berechnet. Die Anwendung nicht konstanter Randbedingungen in der APM erlaubt die Untersuchung des hygrodynamischen Verhaltes von porösen Materialien. In der vorliegenden Studie werden die zeit- und prozeßabhängige Feuchtespeicherung und der Feuchtetransport bestimmt. Die vorgestellten Adsorptions- und Desorptionsexperimente wurden an dem kapillar- aktiven Wärmedämmstoff Calciumsilikat durchgeführt. Die Ergebnisse geben das Hystereseverhalten und den Einfluß der Dynamik der Prozesse wider. In Positionen mit schnellen Feuchteänderungen wird die Feuchtespeicherfunktion im Vergleich mit Regionen langsamer Feuchteänderung nach oben verschoben. Die Feuchteleitfähigkeit als Funktion der relativen Luftfeuchte zeigt eine bedeutende Hysterese. Hingegen ist die Feuchteleitfähigkeit in Relation zum Wassergehalt nicht hysteretisch. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) Experimental determination of the hygroscopie sorption isotherm and the moisture conductvity under transient conditions. By means of the proposed Instantaneous Profile Method (IPM) the relative humidity or the capillary pressure as well as the volumetric water content at specific locations inside a porous medium can be determined. The measurements are carried out under transient conditions and continuously in time. Thus, the IPM allows dynamic measurements of the hygroscopic sorption isotherm and the hygroscopic moisture conductivity. In addition, the moisture conductivity can be obtained via calculation of the moisture flow distribution from the temporal change of moisture contents in the compartments of the sample. The application of non-constant boundary conditions in the IPM allows investigation of the hygrodynamic behaviour of porous materials. In the presented study, the time and process dependent moisture retention characteristic and moisture conductivity are determined. The adsorption and successive desorption experiments presented here have been performed on the capillary active insulation material Calcium Silicate. The results show a hysteretic behaviour with a pregnant influence of the process dynamics. At locations with a rapid moisture increase, the moisture retention characteristic is shifted up in comparison to regions with slow moisture change. The moisture conductivity as function of relative humidity shows a remarkable hysteresis. However, the moisture conductivity in relation to the water content turned out to be non-hysteretic. [source] Fluid Mechanics, Cell Distribution, and Environment in Cell Cube BioreactorsBIOTECHNOLOGY PROGRESS, Issue 1 2003John G. Auni Cultivation of MRC-5 cells and attenuated hepatitis A virus (HAV) for the production of VAQTA, an inactivated HAV vaccine ( 1), is performed in the Cell Cube reactor, a laminar flow fixed-bed bioreactor with an unusual diamond-shaped, diverging-converging flow geometry. These disposable bioreactors have found some popularity for the production of cells and gene therapy vectors at intermediate scales of operation ( 2, 3). Early testing of the Cell Cube revealed that the fluid mechanical environment played a significant role in nonuniform cell distribution patterns generated during the cell growth phase. Specifically, the reactor geometry and manufacturing artifacts, in combination with certain inoculum practices and circulation flow rates, can create cell growth behavior that is not simply explained. Via experimentation and computational fluid dynamics simulations we can account for practically all of the observed cell growth behavior, which appears to be due to a complex mixture of flow distribution, particle deposition under gravity, fluid shear, and possibly nutritional microenvironment. [source] Assessment of microheterogeneity of blood flow in the rat urinary bladder by high-resolution digital radiographyBJU INTERNATIONAL, Issue 6 2005Takahiro Kimura OBJECTIVES To assess high-resolution digital radiography for measuring blood flow and thus examine the microheterogeneity of bladder microcirculation in a rat model. MATERIALS AND METHODS Microheterogeneity of blood flow in both mucosa and detrusor muscle of eight anaesthetized rats was investigated using an imaging technique with very high spatial resolution (0.1 × 0.1 mm2) using digital radiography combined with the deposition of 3H-labelled desmethylimipramine. The spatial pattern of blood flow was quantified by the coefficient of variation of the regional flow (CV = sd/mean). RESULTS Muscle blood flow was less than mucous blood flow (muscle : mucosa, 2.9 : 5) in the empty bladder. In the muscle layer the blood flow distribution was more heterogeneous than that in the mucosa, with a mean (sd) CV in muscle and mucosa of 0.33 (0.033) and 0.16 (0.019), respectively (P < 0.001) at the capillary level. CONCLUSION There was a heterogeneous distribution of blood flow in the microcirculation to capillary vessels in the muscular layer, possibly reflecting a difference in dynamic blood flow of regional perfusion of the emptied bladder. [source] Lung perfusion studies after transcatheter closure of persistent ductus arteriosus with the Amplatzer duct occluder,CATHETERIZATION AND CARDIOVASCULAR INTERVENTIONS, Issue 3 2010Tugcin Bora Polat MD Abstract Background: Reduced left lung perfusion has been described after transcatheter closure of the patent ductus arteriosus (PDA) with several prostheses. Although the Amplatzer ductal occluder (ADO) device is currently the most widely used occluder for closure of large-sized PDAs, the potential consequences of flow distribution to the lungs of this device have not been completely clarified. We evaluated lung perfusion following occlusion of PDA with the ADO device. Methods: Forty-seven patients underwent successful transcatheter PDA occlusion using the ADO device were included in this study. Lung perfusion scans were performed 6 months after the procedure. Results: Decreased perfusion to the left lung (defined as < 40% of total lung flow) was observed in 17 patients (36%), 5 of whom were low-weight symptomatic infants. Ductal ampulla length was significantly shorter and minimal ductal diameter to ampulla diameter ratio was significantly higher in patients with decreased left lung perfusion and correlated well with left lung perfusion values (r = 0.516 and r = ,0.501, respectively). A cut-off value of ,5.8 mm for the ductal ampulla length and ,1.9 for ampulla diameter to ampulla length ratio showed high sensitivity and specificity for reduced lung perfusion. Conclusions: The incidence of abnormal left lung perfusion is high 6 months after transcatheter closure of PDA with the ADO, more likely in the low weight symptomatic infants and in patients with a short duct or a relatively shallow duct having abrupt narrowing of a large ampulla. © 2010 Wiley-Liss, Inc. [source] Hemocompatibility Evaluation With Experimental and Computational Fluid Dynamic Analyses for a Monopivot Circulatory Assist PumpARTIFICIAL ORGANS, Issue 4 2009Masahiro Nishida Abstract:, The hemocompatibility of a newly developed monopivot circulatory assist pump was evaluated by the computational fluid dynamic (CFD) analyses with the particle tracking velocimetry measurement. Results were compared with those of the hemolysis test and in vitro antithrombogenic test to prevent hemolysis and thrombus formation inside the pump. The results of the CFD analysis and the particle tracking velocimetry had a good agreement with each other. The flow distributions by the CFD analysis indicated that the radial jet out of the impeller was adequately weak so that the wall shear stress was lower than 300 Pa on the volute casing wall. It corresponded with the hemolysis tests results, indicating that the hemolysis level was lower than that of the commercially available pump. However, the flow distributions also indicated that the pivot that was easy to stagnate was washed out, not only by the secondary flow through the back gap of the impeller, but also by the vortices generated by the secondary vanes. It corresponded with the in vitro antithrombogenic test results, indicating that thrombus formation could be removed only by redesigning the geometry of the secondary vanes. [source] Using One Rotary Blood Pump to Produce Separate Pulsatile Circulations in the Upper and Lower Halves of the BodyARTIFICIAL ORGANS, Issue 8 2000Takashi Isoyama Abstract: Separate systemic circulations with pulsatile flow were obtained using 1 rotary blood pump as a left ventricular assist device. The outlet of the pump was divided into 2 conduits, 1 connected to the upper half of the body and the other connected to the lower half. An electric actuator that clamped the 2 outlet conduits alternately provided pulsatile flows. An in vitro experiment showed that the pulsatility phases of the upper and lower halves of the body were complementary with pulsatile flow, and an in vivo experiment showed that controlled flow distributions of continuous flows could be obtained. [source] Progress in the Modelling of Air Flow Patterns in Softwood Timber KilnsASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 3-4 2004T.A.G. Langrish Progress in modelling air flow patterns in timber kilns using computational fluid dynamics (CFD) is reviewed in this work. These simulations are intended to predict the distribution of the flow in the fillet spaces between boards in a hydraulic model of a timber kiln. Here, the flow regime between the boards is transitional between laminar and turbulent flow, with Reynolds numbers of the order of 5000. Running the simulation as a transient calculation has shown few problems with convergence issues, reaching a mass residual of 0.2% of the total inflow after 40 to 100 iterations per time step for time steps of 0.01 s. Grid sensitivity studies have shown that non-uniform grids are necessary because of the sudden changes in flow cross section, and the flow simulations are insensitive to grid refinement for non-uniform grids with more than 300,000 cells. The best agreement between the experimentally-measured flow distributions between fillet spaces and those predicted by the simulation have been achieved for (effective) bulk viscosities between the laminar viscosity for water and ten times that value. This change in viscosity is not very large (less than an order of magnitude), given that effective turbulent viscosities are typically several orders of magnitude greater than laminar ones. This result is consistent with the transitional flows here. The effect of weights above the stack can reduce the degree of non-uniformity in air velocities through the stack, especially when thick weights are used, because the stack may then be separated from the eddy at the top of the plenum chamber. [source] | ||||||||||||||||