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Pressure Drop (pressure + drop)
Kinds of Pressure Drop Terms modified by Pressure Drop Selected AbstractsPRESSURE DROP and FRICTION FACTOR IN HELICAL HEAT EXCHANGERS UNDER NONISOTHERMAL and TURBULENT FLOW CONDITIONS,JOURNAL OF FOOD PROCESS ENGINEERING, Issue 3 2003P. CORONEL ABSTRACT This study involved the determination of pressure drop and friction factor (f) in helical heat exchangers under turbulent flow conditions. the experiments were conducted in helical heat exchangers, with coils of two different curvatures ratios (d/D = 0.114 and 0.078) at various flow rates (9.46 × 10,5 - 6.31 × 10,4 m3/s) and end-point temperatures (20, 93.3, 121, 149C). the computed friction factor (f) in the helical heat exchanger was compared to published correlations, and it was found that the experimental data was in good agreement with them. In addition, correlations to determine pressure drop based on the Reynolds number, curvature ratio, and temperature were developed. [source] A mathematical model to describe the change in moisture distribution in maize starch during hydrothermal treatmentINTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 1 2009Ikbal Zarguili Summary Instantaneous Controlled Pressure Drop, ,Détente Instantanée Contrôlée' (DIC) was performed on standard maize starch at residual moisture content (,12%). Changes in moisture distribution were observed during the treatment and modelled through a phenomenological model based on gravimetric data. The model proposes an exponential variation in the moisture content with processing time at various pressures. The predicted data were found to be in good agreement with experimental data. The values of water activity coefficient (,) obtained from the model decrease, when processing pressure increases; 5.86, 3.71 and 3.36 (dry basis),1 for 1, 2 and 3 bar, respectively. The mass transfer coefficient decreases, when the pressure increases. Its value ranged from 5.89 × 10,5 m s,1 for 1 bar down to 0.92 × 10,5 m s,1 for 2 bar and 0.77 × 10,5 m s,1 for 3 bar. This coefficient is not only controlled by a simple resistance to the mass transfer, but also by gelatinisation phenomenon that progresses when temperature increases. [source] The Effect of Particle Size Distribution on Pressure Drop through Packed Beds of Cooked Wood ChipsTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 4 2005Quak Foo Lee Abstract The pressure drop of process liquors through columns of wood chips determines the operability, efficiency and control of both batch and continuous pulp digesters and the quality of the pulp produced from them. Pressure drop was measured through columns of industrial white spruce chips (produced with a chipping head-rig) as a function of the chip size distribution and the extent of delignification. Flow resistance depended on the porosity of the chip bed which was affected by the kappa number of the chips (which affected their flexibility) and chip size distribution, the compaction forces applied to the column, and the liquid superficial velocity. The chip beds were compressible and inelastic. Previous work from the literature using the Ergun equation to characterize pressure losses through chip beds is examined and compared with results of this work. La perte de charge des liqueurs de procédés dans des colonnes de copeaux de bois détermine l'opérabilité, l'efficacité et le contrôle des digesteurs de pâtes discontinus et continus, ainsi que la qualité de la pâte produite. La perte de charge a été mesurée dans des colonnes de copeaux d'épinette (produits avec une machine de fabrication de copeaux) en fonction de la distribution de taille des copeaux et du degré de délignification. La résistance à l'écoulement dépend de la porosité du lit de copeaux qui est influencée par le nombre de kappa des copeaux (qui influe sur leur flexibilité) et la distribution de taille des copeaux, les forces de compaction appliquées à la colonne ainsi que la vitesse de liquide superficielle. Les lits de copeaux sont compressibles et inélastiques. Un travail antérieur de la littérature scientifique faisant appel à l'équation d'Ergun pour caractériser les pertes de charge dans les lits de copeaux est examiné et comparé aux résultats du présent travail. [source] Holdup and Pressure Drop in Vertical and Near-Vertical Three-Phase Up-Flow: A Collection of Flow RegimesASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 1-2 2002P.L. Spedding Three-phase oil, water and air data are reported for vertical and near vertical +86 5° upflow in a 0 026 m i d pipe In general, the liquid holdup for near vertical flow was greater than for the corresponding vertical upflow, the exception being at low liquid and superficial velocities under 0 6 m/s and high superficial gas velocities over 20 m/s Here the liquid holdup varied being sometimes below and other times above the corresponding vertical value These variations of liquid holdup were shown to depend on the fine structure of the flow patterns present The total pressure drop and its component parts showed significantly different patterns of behaviour depending on whether the superficial gas velocity was above or below the rise velocity of a Taylor bubble The total pressure drop generally was greater for near vertical flow compared to the vertical upflow case but reflected changes in the fine structure of the flow patterns A comprehensive collection of flow regimes is included in this paper [source] An Analysis of Pressure Drop and Holdup for Liquid-Liquid Upflow through Vertical PipesCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 7 2007A. K. Jana Abstract The present study has attempted to investigate pressure drop and holdup during simultaneous flow of two liquids through a vertical pipe. The liquids selected were kerosene and water. The measurements were made for phase velocities varying from 0.05,1.2,m/s for both liquids. The pressure drop was measured with a differential pressure transducer while the quick closing valve (QCV) technique was adopted for the measurement of liquid holdup. The measured holdup and pressure drop were analyzed with suitable theoretical models according to the existing flow patterns. The analysis reveals that the homogeneous model is suitable for dispersed bubbly flow whereas bubbly and churn-turbulent flow pattern is better predicted by the drift flux model. On the other hand, the two fluid flow model accurately predicts the pressure drop in core annular flow. [source] Pressure Drop in Liquid-liquid Two Phase Horizontal Flow: Experiment and PredictionCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 9 2005D. P. Chakrabarti Abstract The present study is aimed at an investigation of the pressure drop characteristics during the simultaneous flow of a kerosene-water mixture through a horizontal pipe of 0.025,m diameter. Measurements of pressure gradient were made for different combinations of phase superficial velocities ranging from 0.03,2,m/s such that the regimes encountered were smooth stratified, wavy stratified, three layer flow, plug flow and oil dispersed in water, and water flow patterns. A model was developed, which considered the energy minimization and pressure equalization of both phases. [source] Evaluation of Membrane Oxygenators and Reservoirs in Terms of Capturing Gaseous Microemboli and Pressure DropsARTIFICIAL ORGANS, Issue 11 2009Yulong Guan Abstract An increasing amount of evidence points to cerebral embolization during cardiopulmonary bypass (CPB) as the principal etiologic factor of neurologic complications. In this study, the capability of capturing and classification of gaseous emboli and pressure drop of three different membrane oxygenators (Sorin Apex, Terumo Capiox SX25, Maquet QUADROX) were measured in a simulated adult model of CPB using a novel ultrasound detection and classification quantifier system. The circuit was primed with 1000 mL heparinized human packed red blood cells and 1000 mL lactated Ringer's solution (total volume 2000 mL, corrected hematocrit 26,28%). After the injection of 5 mL air into the venous line, an Emboli Detection and Classification Quantifier was used to simultaneously record microemboli counts at post-pump, post-oxygenator, and post-arterial filter sites. Trials were conducted at normothermic (35°C) and hypothermic (25°C) conditions. Pre-oxygenator and post-oxygenator pressure were recorded in real time and pressure drop was calculated. Maquet QUADROX membrane oxygenator has the lowest pressure drops compared to the other two oxygenators (P < 0.001). The comparison among the three oxygenators indicated better capability of capturing gaseous emboli with the Maquet QUADROX and Terumo Capiox SX25 membrane oxygenator and more emboli may pass through the Sorin Apex membrane oxygenator. Microemboli counts uniformly increased with hypothermic perfusion (25°C). Different types of oxygenators and reservoirs have different capability of capturing gaseous emboli and transmembrane pressure drop. Based on this investigation, Maquet QUADROX membrane oxygenator has the lowest pressure drop and better capability for capturing gaseous microemboli. [source] Convective heat transfer and pressure drop of annular tubes with three different internal longitudinal finsHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 1 2008Lin Tian Abstract Pressure drop and heat transfer characteristics of air in three annular tubes with different internal longitudinal fins were investigated experimentally at uniform wall heat flux. The tested tubes have a double-pipe structure with the inner blocked tube as an insertion. Three different kinds of fins, plain rectangle fin, plain rectangle fin with periodical ridges and wave-like fin, were located peripherally in the annulus. The friction factor and Nusselt number can be corrected by a power-law correction in the Reynolds number range tested. It was found that the tube with periodical ridges on the plain fin or with wave-like fin could augment heat transfer; however, the pressure drop was increased simultaneously. In order to evaluate the comprehensive heat transfer characteristics of the tested tubes, two criteria for evaluating the comprehensive thermal performance of tested tubes were adopted. They are: 1) evaluating the comprehensive heat transfer performance under three conditions: identical mass flow, identical pumping power, and identical pressure drop; 2) the second law of thermodynamics, i.e., the entropy generation. According to the two different evaluating methods, it was found that the tube with wave-like fins provided the most excellent comprehensive heat transfer performance among the three tubes, especially when it was used under higher Reynolds number conditions. © 2007 Wiley Periodicals, Inc. Heat Trans Asian Res, 37(1): 29,40, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20186 [source] The Effect of Particle Size Distribution on Pressure Drop through Packed Beds of Cooked Wood ChipsTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 4 2005Quak Foo Lee Abstract The pressure drop of process liquors through columns of wood chips determines the operability, efficiency and control of both batch and continuous pulp digesters and the quality of the pulp produced from them. Pressure drop was measured through columns of industrial white spruce chips (produced with a chipping head-rig) as a function of the chip size distribution and the extent of delignification. Flow resistance depended on the porosity of the chip bed which was affected by the kappa number of the chips (which affected their flexibility) and chip size distribution, the compaction forces applied to the column, and the liquid superficial velocity. The chip beds were compressible and inelastic. Previous work from the literature using the Ergun equation to characterize pressure losses through chip beds is examined and compared with results of this work. La perte de charge des liqueurs de procédés dans des colonnes de copeaux de bois détermine l'opérabilité, l'efficacité et le contrôle des digesteurs de pâtes discontinus et continus, ainsi que la qualité de la pâte produite. La perte de charge a été mesurée dans des colonnes de copeaux d'épinette (produits avec une machine de fabrication de copeaux) en fonction de la distribution de taille des copeaux et du degré de délignification. La résistance à l'écoulement dépend de la porosité du lit de copeaux qui est influencée par le nombre de kappa des copeaux (qui influe sur leur flexibilité) et la distribution de taille des copeaux, les forces de compaction appliquées à la colonne ainsi que la vitesse de liquide superficielle. Les lits de copeaux sont compressibles et inélastiques. Un travail antérieur de la littérature scientifique faisant appel à l'équation d'Ergun pour caractériser les pertes de charge dans les lits de copeaux est examiné et comparé aux résultats du présent travail. [source] Comparison of Pumps and Oxygenators With Pulsatile and Nonpulsatile Modes in an Infant Cardiopulmonary Bypass ModelARTIFICIAL ORGANS, Issue 11 2009Nikkole M. Haines Abstract As the evidence mounts in favor of pulsatile perfusion during CPB, it is necessary to investigate the effect of circuit components on the quality of pulsatility delivered throughout the circuit. We compared two bloodpumps, the Jostra HL-20 heart-lung machine and the MEDOS DELTASTREAM DP1 Bloodpump, and two oxygenators, the Capiox Baby RX05 and the MEDOS HILITE 800LT, in terms of mean arterial pressure, energy equivalent pressure, surplus hemodynamic energy, total hemodynamic energy, and pressure drop over the oxygenators using a blood analog. The pumps and oxygenators were combined in unique circuits and tested in nonpulsatile and pulsatile modes, at two flow rates (500 and 800 mL/min), and three rotational speed differentials when using the MEDOS DELTASTREAM DP1 Bloodpump for 144 trials in total. The Jostra Roller pump produced some pulsatility in nonpulsatile mode and better pulsatility in pulsatile mode than the MEDOS DP1 Bloodpump at a rotational speed differential of 2500 rpm, but not at 3500 or 4500 rpm. The MEDOS DP1 Bloodpump produced almost no pulsatility in nonpulsatile mode. Pressure drops over the Capiox Baby RX05 were markedly higher, at 92.5 ± 0.4 mm Hg with the MEDOS DP1 Bloodpump at 800 mL/min and 4500 rpm in pulsatile mode, than those of the MEDOS HILITE 800LT oxygenator, which was 67.0 ± 0.1 mm Hg at the same settings. These results suggest that careful selection of each circuit component, based on the individual clinical case and component specifics, are necessary to achieve the best quality of pulsatility. [source] Hydrodynamics and Flow Development in a 15.1,m Circulating Fluidized Bed RiserCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 4 2007W.-X. Huang Abstract Hydrodynamics and flow development are studied in a long riser circulating fluidized bed reactor (15.1,m). Optic fiber probes were used for the measurement of local solids distribution. Pressure drops were also measured with pressure transducers along the riser. The flow development in the riser center is almost instant with solids holdup remaining constant and low, and particle velocity remaining high along the riser. The particle flow is firstly developed from center, and then towards the wall. The riser height is an important factor for the design of circulating fluidized bed reactors. Increasing the solid circulating rate significantly slows down the flow development process, while increases in the superficial gas velocity accelerate it. [source] 5-Hydroxytryptamine-induced microvascular pressure transients in lungs of anaesthetized rabbitsACTA PHYSIOLOGICA, Issue 2 2001N. Sen We determined lung microvascular pressure transients induced by 5-hydroxytryptamine (5HT), by the micropuncture technique. We mechanically ventilated anaesthetized (halothane 0.8%), open-chested rabbits, in which we recorded pulmonary artery (PA), left atrial (LA) and carotid artery pressures and cardiac output. For 4-min periods of stopped ventilation, we constantly inflated the lung with airway pressure of 7 cmH2O, then micropunctured the lung to determine pressures in arterioles and venules of 20,25 ,m diameter. An intravenous bolus infusion of 5HT (100 ,g), increased total pulmonary vascular resistance by 59%. Prior to 5HT infusion, the arterial, microvascular and venous segments comprised 30, 50 and 19% of the total pulmonary vascular pressure drop, respectively. However 14 s after 5HT infusion, the PA-arteriole pressure difference (arterial pressure drop) increased 46%, while the venule-LA pressure difference (venous pressure drop) increased >100%. The arteriole,venule pressure difference (microvascular pressure drop) was abolished. The increase in the arterial pressure drop was maintained for 4.8 min, whereas the increased venous pressure drop reverted to baseline in <1 min. We conclude that in the rabbit lung in situ, a 5HT bolus causes sustained arterial constriction and a strong but transient venous constriction. [source] Sustained increase in arterial blood pressure and vascular resistance induced by infusion of arachidonic acid in ratsACTA PHYSIOLOGICA, Issue 1 2000Kirkebø The haemodynamic responses to arachidonic acid (AA) have been investigated in seven groups of anaesthetized rats. Sodium arachidonate was infused intravenously for 4 or 20 min, and arterial blood pressure was recorded continuously. Cardiac output and organ blood flow were measured by microspheres. Infusion of arachidonate caused first a fast drop in arterial blood pressure, thereafter it increased steadily for 5,15 min towards a pressure about 25 mmHg above control level. The high pressure was maintained for at least 1 h. Repeated infusions of arachidonate gave similar responses. Inhibition of cyclo-oxygenase by indomethacin prevented the initial pressure drop to arachidonate, but not the sustained increase in pressure. Arterial pressure, total vascular resistance and blood flow in the kidneys, adrenals and spleen were significantly reduced, whereas cardiac output was not changed 4 min after start infusion of arachidonate. However, average blood pressure was significantly increased 22 and 35 min after start infusion (from 103.9 ± 2.9 to 128.1 ± 6.1 and 135.8 ± 4.6 mmHg). Mean vascular resistance increased simultaneously (from 3.5 ± 0.2 to 4.7 ± 0.4 and 5.2 ± 0.4 mmHg 100 mL,1), while cardiac output, stroke volume and heart rate were maintained or slightly reduced. The renal blood flow was significantly lowered (from average 4.9 ± 0.1 to 3.3 ± 0.2 and 4.0 ± 0.2 mL min,1). Indomethacin did not prevent the changes in vascular resistance or organ blood flow recorded after 20,35 min. On the other hand, inhibition of both cyclo-oxygenase, lipoxygenase and the cytochrome P450 pathways by eicosatetrayonic acid (ETYA) normalized all haemodynamic parameters. Likewise, the rise in pressure was prevented by 17-octadecynoic acid (17-ODYA), an inhibitor of the cytochrome P450 enzyme activity. Thus, arachidonate infusion caused a transient decrease, and then a sustained increase in arterial pressure and vascular resistance, and a long-lasting reduction in renal blood flow, possibly owing to release of a cytochrome P450 dependent vasoconstrictor metabolite of AA. [source] Photobleaching-based flow measurement in a commercial capillary electrophoresis chip instrumentELECTROPHORESIS, Issue 6 2008Guiren R. Wang Professor Abstract For microfluidic analytical instruments, a facile, fast, and accurate instrument test is highly demanded. The test includes the quantitative verification of the relationship between pressure drop and flow velocity for the hydrodynamic pump, between the electric voltage and electroosmotic flow (EOF) for the high-voltage supply, and the chip quality. The key point for the test is the measurement of the flow velocity. However, most currently available velocimetries cannot be directly used without any instrumental modification or adding extra instruments. We applied a recently developed Laser Induced Fluorescence Photobleaching Anemometer (LIFPA) for the instrument test through measuring fluid flow velocity in a microfluidic instrument with optical measurement without any modification and extra instrument. We have successfully used the method to test Caliper HTS 250 System from Caliper Life Sciences (Hopkinton, MA) with its own light source and detector. The experimental result demonstrates that this single-point method of measuring flow velocity can be easily used for accurate test of a microfluidic instrument in less than 10,min at extremely low cost without any modification and extra instrument. [source] Baghouse system design based on economic optimizationENVIRONMENTAL PROGRESS & SUSTAINABLE ENERGY, Issue 4 2000Antonio C. Caputo In this paper a method is described for using economic optimization in the design of baghouse systems. That is, for a given emission control problem, the total filtration surface area, the overall pressure drop, fabric material effects, and the cleaning cycle frequency, may all be evaluated simultaneously. In fact, as baghouse design parameters affect capital and operating expenses in interrelated and counteracting manners, a minimum total cost may be searched defining the best arrangement of dust collection devices. With this in mind, detailed cost functions have been developed with the aim of providing an overall economic model. As a result, a discounted total annual cost has been obtained that may be minimized by allowing for optimal baghouse characterization. Finally, in order to highlight the capabilities of the proposed methodology, some optimized solutions are also presented, which consider the economic impact of both bag materials and dust properties. [source] Convective heat transfer and pressure drop of annular tubes with three different internal longitudinal finsHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 1 2008Lin Tian Abstract Pressure drop and heat transfer characteristics of air in three annular tubes with different internal longitudinal fins were investigated experimentally at uniform wall heat flux. The tested tubes have a double-pipe structure with the inner blocked tube as an insertion. Three different kinds of fins, plain rectangle fin, plain rectangle fin with periodical ridges and wave-like fin, were located peripherally in the annulus. The friction factor and Nusselt number can be corrected by a power-law correction in the Reynolds number range tested. It was found that the tube with periodical ridges on the plain fin or with wave-like fin could augment heat transfer; however, the pressure drop was increased simultaneously. In order to evaluate the comprehensive heat transfer characteristics of the tested tubes, two criteria for evaluating the comprehensive thermal performance of tested tubes were adopted. They are: 1) evaluating the comprehensive heat transfer performance under three conditions: identical mass flow, identical pumping power, and identical pressure drop; 2) the second law of thermodynamics, i.e., the entropy generation. According to the two different evaluating methods, it was found that the tube with wave-like fins provided the most excellent comprehensive heat transfer performance among the three tubes, especially when it was used under higher Reynolds number conditions. © 2007 Wiley Periodicals, Inc. Heat Trans Asian Res, 37(1): 29,40, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20186 [source] Experimental study of the flow boiling heat transfer enhancement and pressure drop due to the bubble behavior restricted by a screen sheetHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 4 2003Katsuhiko Kadoguchi Abstract A unique method previously proposed by the authors was applied to the heat transfer augmentation in the flow boiling field. In this method a screen sheet was placed on the horizontal heated surface where bubble nucleation occurred. Generated vapor bubbles were trapped between the screen and the wall, became flat, and moved along the surface. This restricted bubble behavior caused the heat transfer enhancement. Three types of screen sheet were tested in the present experiment and the effect of the screen on the heat transfer and two-phase flow characteristics was investigated. In two of these cases, the screen was displaced upward by the bubble nucleation. Compared with the ordinary flow boiling case, heat transfer was enhanced by a factor of 1.2 to 6 within the present experimental range. Using a simple flow model, it was made clear that the effect of the height of the displaced screen was important in evaluating the increase in pressure drop. © 2003 Wiley Periodicals, Inc. Heat Trans Asian Res, 32(4): 319,329, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.10094 [source] The scaling law in the hole erosion test with a constant pressure dropINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 13 2008Stéphane Bonelli Abstract A process called ,piping', which often occurs in the soil at dams, levees, and dykes, involves the formation and development of a continuous tunnel between upstream and downstream ends. The hole erosion test is commonly used to quantify the critical stress and the rate of piping erosion progression. The aim of this study is to draw up a model for interpreting the results of this test. A characteristic internal erosion time is defined and expressed as a function of the initial hydraulic gradient and the coefficient of surface erosion. It is established here that the product of the coefficient of erosion and the flow velocity is a significant dimensionless number: when this number is small, the kinetics of erosion are low, and the particle concentration does not have any effect on the flow. This finding applies to most of the available test results. Theoretical and experimental evidence is presented showing that the evolution of the pipe radius during erosion with a constant pressure drop obeys a scaling exponential law. Copyright © 2008 John Wiley & Sons, Ltd. [source] Laminar and turbulent flow calculations through a model human upper airway using unstructured meshesINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 12 2007P. Nithiarasu Abstract In this paper, numerical investigation of airflow through a human upper airway is presented using an unstructured-based characteristic-based split (CBS) scheme. The CBS scheme used in the present study employs a fully explicit matrix-free solution procedure along with artificial compressibility. A one equation Spalrat,Allmaras (SA) turbulence model is employed to study low and moderate Reynolds number flows. A detailed discussion of the qualitative and quantitative results is presented. The results show a strong influence of the Reynolds number on the flow pattern and quantities of interest, pressure drop and wall shear stress. It is also apparent that SA model can be employed on unstructured meshes to predict the steady flow with good accuracy. Thus, the novelties of the present paper are: use of the unstructured mesh-based solution algorithm and the successful application of the SA model to a typical human upper airway. Copyright © 2006 John Wiley & Sons, Ltd. [source] Topology optimization of microfluidic mixersINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 5 2009Casper Schousboe Andreasen Abstract This paper demonstrates the application of the topology optimization method as a general and systematic approach for microfluidic mixer design. The mixing process is modeled as convection dominated transport in low Reynolds number incompressible flow. The mixer performance is maximized by altering the layout of flow/non-flow regions subject to a constraint on the pressure drop between inlet and outlet. For a square cross-sectioned pipe the mixing is increased by 70% compared with a straight pipe at the cost of a 2.5 fold increase in pressure drop. Another example where only the bottom profile of the channel is a design domain results in intricate herring bone patterns that confirm findings from the literature. Copyright © 2008 John Wiley & Sons, Ltd. [source] Method of fundamental solutions for partial-slip fibrous filtration flowsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 3 2009Shunliu Zhao Abstract In this study a Stokeslet-based method of fundamental solutions (MFS) for two-dimensional low Reynolds number partial-slip flows has been developed. First, the flow past an infinitely long cylinder is selected as a benchmark. The numerical accuracy is investigated in terms of the location and the number of the Stokeslets. The benchmark study shows that the numerical accuracy increases when the Stokeslets are submerged deeper beneath the cylinder surface, as long as the formed linear system remains numerically solvable. The maximum submergence depth increases with the decrease in the number of Stokeslets. As a result, the numerical accuracy does not deteriorate with the dramatic decrease in the number of Stokeslets. A relatively small number of Stokeslets with a substantial submergence depth is thus chosen for modeling fibrous filtration flows. The developed methodology is further examined by application to Taylor,Couette flows. A good agreement between the numerical and analytical results is observed for no-slip and partial-slip boundary conditions. Next, the flow about a representative set of infinitely long cylindrical fibers confined between two planar walls is considered to represent the fibrous filter flow. The obtained flowfield and pressure drop agree very well with the experimental data for this setup of fibers. The developed MFS with submerged Stokeslets is then applied to partial-slip flows about fibers to investigate the slip effect at fiber,fluid interface on the pressure drop. The numerical results compare qualitatively with the analytical solution available for the limit case of infinite number of fibers. Copyright © 2008 John Wiley & Sons, Ltd. [source] A numerical study of an unsteady laminar flow in a doubly constricted 3D vesselINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 12 2002B. V. Rathish Kumar Abstract Unsteady flow dynamics in doubly constricted 3D vessels have been investigated under pulsatile flow conditions for a full cycle of period T. The coupled non-linear partial differential equations governing the mass and momentum of a viscous incompressible fluid has been numerically analyzed by a time accurate Finite Volume Scheme in an implicit Euler time marching setting. Roe's flux difference splitting of non-linear terms and the pseudo-compressibility technique employed in the current numerical scheme makes it robust both in space and time. Computational experiments are carried out to assess the influence of Reynolds' number and the spacing between two mild constrictions on the pressure drop across the constrictions. The study reveals that the pressure drop across a series of mild constrictions can get physiologically critical and is also found to be sensitive both to the spacing between the constrictions and the oscillatory nature of the inflow profile. The flow separation zone on the downstream constriction is seen to detach from the diverging wall of the constriction leading to vortex shedding with 3D features earlier than that on the wall in the spacing between the two constrictions. Copyright © 2002 John Wiley & Sons, Ltd. [source] Performance improvement of the vapour compression refrigeration cycle by a two-phase constant area ejectorINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 5 2009Nagihan Bilir Abstract The performance of a vapour compression system that uses an ejector as an expansion device was investigated. In the analysis, a two-phase constant area ejector flow model was used. R134a was selected as the refrigerant. According to the obtained results, for any operating temperature there are different optimum values of pressure drop in the suction chamber, ejector area ratio, ejector outlet pressure and cooling coefficient of performance (COP). As the difference between condenser and evaporator temperatures increases, the improvement ratio in COP rises whereas ejector area ratio drops. The minimum COP improvement ratio in the investigated field was 10.1%, while its maximum was 22.34%. Even in the case of an off-design operation, the performance of a system with ejector is higher than that of the basic system. 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] A parametric study of multi-phase and multi-species transport in the cathode of PEM fuel cellsINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 8 2008Nada Zamel Abstract In this study, a mathematical model is developed for the cathode of PEM fuel cells, including multi-phase and multi-species transport and electrochemical reaction under the isothermal and steady-state conditions. The conservation equations for mass, momentum, species and charge are solved using the commercial software COMSOL Multiphysics. The catalyst layer is modeled as a finite domain and assumed to be composed of a uniform distribution of supported catalyst, liquid water, electrolyte and void space. The Stefan,Maxwell equation is used to model the multi-species diffusion in the gas diffusion and catalyst layers. Owing to the low relative species' velocity, Darcy's law is used to describe the transport of gas and liquid phases in the gas diffusion and catalyst layers. A serpentine flow field is considered to distribute the oxidant over the active cathode electrode surface, with pressure loss in the flow direction along the channel. The dependency of the capillary pressure on the saturation is modeled using the Leverette function and the Brooks and Corey relation. A parametric study is carried out to investigate the effects of pressure drop in the flow channel, permeability, inlet relative humidity and shoulder/channel width ratio on the performance of the cell and the transport of liquid water. An inlet relative humidity of 90 and 80% leads to the highest performance in the cathode. Owing to liquid water evaporation, the relative humidity in the catalyst layer reaches 100% with an inlet relative humidity of 90 and 80%, resulting in a high electrolyte conductivity. The electrolyte conductivity plays a significant role in determining the overall performance up to a point. Further, the catalyst layer is found to be important in controlling the water concentration in the cell. The cross-flow phenomenon is shown to enhance the removal of liquid water from the cell. Moreover, a shoulder/channel width ratio of 1:2 is found to be an optimal ratio. A decrease in the shoulder/channel ratio results in an increase in performance and an increase in cross flow. Finally, the Leverette function leads to lower liquid water saturations in the backing and catalyst layers than the Brooks and Corey relation. The overall trend, however, is similar for both functions. Copyright © 2007 John Wiley & Sons, Ltd. [source] The influence of rotary valve distribution systems on the energetic efficiency of regenerative thermal oxidizers (RTO)INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 1 2008Mario Amelio Abstract On,off valve systems, commonly used in regenerative thermal oxidizer (RTO) plants, generate, during the opening time, a mass flow rate (MFR) which is constant. On the contrary, rotary valve systems, which are increasingly adopted in RTO plants, are characterized by variable MFR profiles. In this work, the energy requirements of two RTO systems, equipped with on,off or rotary valves, were determined using a home-developed numerical code. Energy performances were evaluated by calculating the thermal efficiency and pressure drop within structured or random packed bed RTO systems, at the same mean MFR. The results demonstrated that thermal efficiency was only moderately influenced by the valve system, and is slightly lower for the RTO with on,off valve. On the other hand, the study revealed that energy requirements of all RTO systems were basically unaffected by cycle duration, allowing valve rotational velocity to be freely set to maximize for other technical requirements. On the contrary, pressure drop was greatly influenced by the valve type and increased as variability in MFR function augmented. Moreover, the type of regenerator, structured or random packed bed, affected differently the total energy requirements (basically pumping energy plus auxiliary fuel). Energy requirements of structured and random regenerators were comparable only when volatile organic compounds concentration was lower than typical values encountered in the industrial practise. In other cases, structured regenerators RTO were more competitive. Finally, structured regenerators are usually the best choice when rotating valve distribution systems are adopted. Copyright © 2007 John Wiley & Sons, Ltd. [source] Optimization of a finned heat sink array based on thermoeconomic analysisINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 5 2007S. Z. Shuja Abstract The design and specification of heat sinks for electronic systems is not easily accomplished through the use of standard thermal design and analysis tools since geometric and boundary conditions are not typically known in advance. A second-law based thermoeconomic optimization procedure is presented for a finned heat sink array. This involves including costs associated with material, and irreversible losses due to heat transfer and pressure drop. The influence of important physical, geometrical and unit cost parameters on the overall finned array are optimized for some typical operating conditions that are representative of electronic cooling applications. The optimized cost results are presented in terms of ReD, ReL, ,P / ,H, and q for a finned system in a graphical form. In addition the methodology of obtaining optimum parameters for a finned heat sink system which will result in minimum operating cost is demonstrated. Copyright © 2006 John Wiley & Sons, Ltd. [source] Influence of magnetic field on two-phase flow convective boiling of some refrigerant mixturesINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 15 2005Samuel M. Sami Abstract In this paper, an experimental study on the influence of magnetohydrodynamic (MHD) on heat transfer characteristics of two-phase flow boiling of some refrigerant mixtures in air/refrigerant horizontal enhanced surface tubing is presented. Correlations were proposed to predict the impact of MHD on the heat transfer characteristics such as average heat transfer coefficients, and pressure drops of R-507, R-404A, R-410A, and R-407C in two-phase flow boiling inside enhanced surface tubing. In addition, it was found that the refrigerant mixture's pressure drop is a weak function of the mixture's composition. It was also evident that the proposed correlations for predicting the heat transfer characteristics were applicable to the entire heat and mass flux, investigated in the present study. The deviation between the experimental and predicted value using new and improved correlations for the heat transfer coefficient and pressure drop were less than ±20%, for the majority of data. Copyright © 2005 John Wiley & Sons, Ltd. [source] Along-channel mathematical modelling for proton exchange membrane fuel cellsINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 12 2005Wenbo Huang Abstract Proper water and thermal management is essential for obtaining high performance of proton exchange membrane fuel cells (PEMFCs). A steady, two-dimensional water and thermal management model was developed, aiming at considering pressure effects (i.e. the effects of local pressure on the cell performance), pressure drop, open circuit voltage variation with stack temperature, water vapour effects on membrane conductivity, which made the model physically more reasonable and more suitable for various operating conditions. The model could predict the distributions of a series of important parameters along the flow channel, and thus the effects of various operating and design parameters on the fuel cell performance could be investigated easily by numerical trial-and-error method. The modelling results compared well with the available experimental results from the literatures. The results also showed that the humidification of both anode and cathode is crucial for the performance of PEMFCs. The model could be a very useful engineering tool for the optimization of PEMFCs. Copyright © 2005 John Wiley & Sons, Ltd. [source] Flows through horizontal channels of porous materialsINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 10 2003A.K. Al-Hadhrami Abstract In this paper, the control volume method (CVM) with the staggered grid system is utilized to solve the two-dimensional Brinkman equation for different configurations of porous media in a horizontal channel. The values of the permeability of sand and clear fluid are considered when performing several numerical investigations which enable the evaluation of the behaviour of the flow through regions that mathematically model some geological features (faults/fractures) present in oil reservoirs or groundwater flows. We have found that the convergence of the CVM can be achieved within a reasonable number of iterations when there is a gap present between a partial barrier of low Darcy number and the channel boundary. However, a complete barrier across the channel results in a very high resistance and hence there is a large pressure drop which causes difficulties in convergence. In order to improve the rate of convergence in such situations, an average pressure correction (APC) technique, which is based on global mass conservation, is developed. The use of this technique, along with the CVM, can rapidly build up the pressure drop across such a barrier and hence dramatically improve the rate of convergence of the iterative scheme. Copyright © 2003 John Wiley & Sons, Ltd. [source] | |||||||||||||||||||||||||||||||||||||