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Diameter Ratio (diameter + ratio)
Selected AbstractsEstimation of Joule heating effect on temperature and pressure distribution in electrokinetic-driven microchannel flowsELECTROPHORESIS, Issue 3 2006Reiyu Chein Professor Abstract In this study we present simple analytical models that predict the temperature and pressure variations in electrokinetic-driven microchannel flow under the Joule heating effect. For temperature prediction, a simple model shows that the temperature is related to the Joule heating parameter, autothermal Joule heating parameter, external cooling parameter, Peclet number, and the channel length to channel hydraulic diameter ratio. The simple model overpredicted the thermally developed temperature compared with the full numerical simulation, but in good agreement with the experimental measurements. The factors that affect the external cooling parameters, such as the heat transfer coefficient, channel configuration, and channel material are also examined based on this simple model. Based on the mass conservation, a simple model is developed that predicts the pressure variations, including the temperature effect. An adverse pressure gradient is required to satisfy the mass conservation requirement. The temperature effect on the pressure gradient is via the temperature-dependent fluid viscosity and electroosmotic velocity. [source] Combustion behavior of a falling sodium droplet: Burning rate-constant and drag coefficientHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 7 2005Atsushi Makino Abstract The combustion behavior of a single sodium droplet has been studied experimentally, by use of a falling droplet. It was found that D2 -law can hold for the sodium droplet combustion after the ignition, which can be observed to occur through an increase in the droplet temperature under a condition without a gaseous flame, suggesting that a surface reaction plays an important role in the ignition of sodium. It was also found that the burning rate-constant without forced convection has nearly the same value as those for conventional hydrocarbon droplets, although it is considered that the sodium combustion proceeds in an oxidizer-rich environment even in the air. This can be judged by comparing a temporal variation of the flame/droplet diameter ratio for the sodium droplet with that for the hydrocarbon droplet. A micro-explosion of the burning droplet is also observed when oxygen concentration in the ambience exceeds 0.33 in mass fraction. As for the falling velocity and/or distance of the burning droplet, it turned out that the use of the drag coefficient for solid sphere under isothermal condition is inappropriate in obtaining accurate values. It was also found in another experiment that when Re > 500, the drag coefficient of the falling droplet undergoing combustion is as high as 2 depending on combustion situation and/or droplet temperature, while that of the solid sphere under an isothermal condition is 0.44. © 2005 Wiley Periodicals, Inc. Heat Trans Asian Res, 34(7): 481,495, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20084 [source] Heat transfer on tube bundles embedded horizontally in a liquid-fluidized bedHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 2 2005Kenichi Hashizume Abstract Heat transfer on tube bundles embedded horizontally in a liquid-fluidized bed was investigated experimentally. In the experiment, a total of 5 kinds of tube bundles in an equilateral triangular staggered arrangement, including a single tube, was used. Tested particles were of glass and ceramics, and their diameter range was from 2.1 to 6.0 mm. It was found that the distribution of local heat transfer coefficients around a tube depends not on the kind of particles, but on the tube pitch only, when a good fluidizing condition is maintained. Based on the experimental data, a new method was proposed to predict average heat transfer coefficient, which can be applicable for tube bundles having a tube pitch to diameter ratio of 1.2 to infinity (single tube). © 2005 Wiley Periodicals, Inc. Heat Trans Asian Res, 34(2): 85,98, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20048 [source] Annular liquid jets at high Reynolds numbersINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 2 2003G. Georgiou Abstract The flow of annular liquid jets at high Reynolds numbers is analysed by means of the finite element method and the full-Newton iteration scheme. Results have been obtained for various values of the inner to the outer diameter ratio and for non-zero surface tension, using extremely long meshes. The annular film moves far from the symmetry axis at low values of the Reynolds number. At higher Reynolds numbers, the film moves towards the axis of symmetry and appears close to very far downstream, forming a round jet. Asymptotic results for the radius of the resulting round jet are provided. Copyright © 2003 John Wiley & Sons, Ltd. [source] Rules-of-thumb of implementing short electric band heaters (length to diameter ratio <1.5) for external heating of pipe flowsINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 2 2002X. D. Chen Abstract Short electric band heaters (L/Di<1.5) are constructed for the ease of implementation in small scale heating applications. They are usually mounted side-by-side in series along the external wall of a pipe for heating the fluid within the pipe. There are no rules-of-thumb available about designing such a system to achieve good uniformity of the temperature profile at the pipe inner surface beforehand. Non-uniformity can cause preferential fouling at hotter spots. This study focuses on the axial uniformity of heating along a pipe inside which the heated fluid if flowing. The situation has been simplified a great deal in mathematical terms from the corresponding conventional conjugate problem considered previously due to the small temperature rise in the fluid flow through one section of the pipe which is heated by one band heater. Similarity parameter sets have been deduced and verified by numerical simulations. The worst scenario of non-uniformity for such short band heaters, that is when L/Di=1.5, is presented in this paper. This may be used for designing a system to minimize the non-uniformity in terms of choosing the right pipe material, percentage of heater wire coverage in the band heater, etc. Copyright © 2002 John Wiley & Sons, Ltd. [source] Gray-scale sonography of solid breast masses: Diagnosis of probably benign masses and reduction of the number of biopsiesJOURNAL OF CLINICAL ULTRASOUND, Issue 1 2007Luciano Chala MD Abstract Purpose. To identify probably benign breast masses using gray-scale sonography and to see if this strategy could reduce the number of biopsies of breast masses. Methods. This retrospective study included 229 masses in 203 women who underwent sonographically guided percutaneous biopsy. Masses with a negative predictive value for malignancy >98% were retrospectively considered probably benign, and the potential impact of gray-scale sonography in reducing the number of biopsies if these masses were not biopsied was assessed. Assessments were performed considering all masses as a group as well as various subgroups. Results. Round, ellipsoid, or lobulated masses with 3 or fewer lobulations, circumscribed margins, a longitudinal,anteroposterior diameter ratio ,1.0 and no marked hypoechogenicity, posterior acoustic shad owing, internal microcalcifications, or altered surrounding breast tissue were considered probably benign. The sensitivity of gray-scale sonography to identify this subgroup was 98%, with a negative predictive value of 99%. If these masses were not biopsied, there would be a 42% reduction in the number of biopsies considering all masses, a 36% reduction for masses classified as Breast Imaging Reporting and Data System category 4, and a 59% reduction for masses exclusively analyzed with sonography. Conclusions. It is possible to identify probably benign breast masses using gray-scale sonography, and thereby to reduce the number of biopsies performed. © 2006 Wiley Periodicals, Inc. J Clin Ultrasound 2007 [source] Molecular simulation of complete phase diagrams for binary mixturesAICHE JOURNAL, Issue 7 2001Monica H. Lamm Vapor-liquid, vapor-solid and liquid-solid coexistence lines are calculated for binary mixtures of Lennard-Jones spheres using Monte Carlo simulation and the Gibbs-Duhem integration technique. Complete phase diagrams showing equilibrium between vapor, liquid and solid phases are constructed for binary Lennard-Jones mixtures with diameter ratios ranging from ,11 /,22 = 0.85,1.0 and attractive well-depth ratios ranging from ,11/,22 = 0.625,1.6, at a reduced pressure P*,P,/,11 = 0.002. The Lorentz-Berthelot combining rules are used to calculate the cross-species interaction parameters ,12 and ,12. The variation in the shape of the complete phase diagrams change as a function of the diameter ratio ,11 /,22 and well-depth ratio ,11 /,22 is systematically explored. The phase diagrams found here resemble those found experimentally for argon-methane, iodine-sulfur, water-sodium chloride, water-silver nitrate, water-potassium nitrate, and p-dichlorobenzene-p-dibromobenzene. [source] Property-averaging applied to determination of volume contraction in binary-solid liquid-fluidized bedsTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2008Renaud Escudié Abstract This communication examines experimental information from the literature on the volume contraction that can occur when two monocomponent particle species that have a diameter ratio and a buoyancy-corrected density ratio on opposite sides of unity are subjected to liquid fluidization as a binary mixture. Attempts are made to predict this volume contraction by applying monocomponent bed expansion equations using averaged properties of the binary solids. It was found that this method works better if the equations are anchored to experimental monocomponent voidages by the fractional bed volume change that they predict than if the equations are used directly. However, greater prediction accuracy can be achieved by correlation of the adjustable parameter G of the Westman, Am Ceramic Soc, 19, 127,129, (1936) equation, originally applied to binary packed beds. On examine dans cet article des données expérimentales de la littérature scientifique sur la contraction de volume qui peut survenir lorsque deux espèces de particules à composante unique d'un rapport de diamètre et d'un rapport de masse volumique corrigé par la flottabilité plus grands et plus petits que l'unité sont soumises à une fluidisation de liquide comme un mélange binaire. On tente de prédire cette contraction de volume en appliquant des équations d'expansion de lit dans le cas monocomposant et en utilisant les propriétés moyennées des solides binaires. On a trouvé que cette méthode fonctionnait mieux lorsque les équations sont étroitement liées aux degrés de vide monocomposants expérimentaux par le changement de volume de lit factionnaire qu'elles prédisent, que lorsque ces équations sont utilisées directement. Néanmoins, une meilleure précision dans la prédiction peut être obtenue par la corrélation de l'équation du paramètre G ajustable de Westman, Am Ceramic Soc, 19, 127,129, (1936), appliquée originellement aux lits garnis binaires. [source] Solids suspension agitation in square tanksTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 1 2008Emily T. Mitchell Abstract The Zwietering correlation for the just-suspended speed has been modified to include baffling and geometric effects (impeller-to-tank diameter ratio and impeller off-bottom clearance) for two impeller types (high-efficiency and pitched-blade). Baffles are generally not required when using square tanks although they improve solids suspension performance of pitched-blade turbines. Comparison of square tank solids suspension to that in a fully baffled cylindrical tank has also been made. Very little difference was observed in the power number, but the just-suspended speed, torque, and power requirements were higher in the square tank. On a modifié la corrélation de Zwietering pour la vitesse de suspension minimale afin d'inclure les effets des contrepales et de la geométrie (rapport du diamètre turbine sur réservoir et dégagement de la turbine par rapport au fond) pour deux types de turbines (à efficacité élevée et à pales inclinées). II n'est généralement pas nécessaire d'installer des contrepales dans le cas de réservoirs carrés bien que celles-ci améliorent la performance de la suspension de solides dans le cas des turbines à pales inclinées. On a également comparé la suspension de solides dans un réservoir carré à celle d'un réservoir cylindrique muni de quatre chicanes. Une très faible différence a été observée dans le nombre de puissance, mais la vitesse de suspension minimale, le couple et la demande en puissance sont plus élevés dans le réservoir carré. [source] Extension to mixtures of two robust hard-sphere equations of state satisfying the ordered close-packed limitTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 4 2001Cyrus Ghotbi Abstract Two new hard-sphere EOS are proposed and tested using the same attractive potential terms used by the SAFT EOS. Generalized expressions for the pair RDF at contact value, the compressibility factor, and the excess chemical potentials have been derived. Extension to mixtures is tested using three mixing rules for multicomponent hard-sphere fluids. The proposed EOS combined with the Santos et al. and the Barrio-Solana mixing rules reproduced the compressibility factors and the excess chemical potentials more accurately than the Boublik-Mansoori-Camahan-Starling-Leland (BMCSL) EOS. However the pair RDF at contact value had larger deviations than those obtained with the BMCSL EOS. The combination of the proposed equations and the Barrio-Solana mixing rule gave an accurate reproduction of the compressibility factor for binary hard-sphere fluids with high diameter ratio even in the low concentration regions of the larger spheres. Deux nouvelles équations d'état de sphères dures sont proposées et vérifiées à l'aide des m,mes termes potentiels attractifs utilisés pour l'équation d'état de SAFT. Des expressions généralisées pour le RDF pair à la valeur de contact, le facteur de compressibilité et les potentiels chimiques d'excès ont été calculées. L'extension à des mélanges est vérifiée à l'aide de trois régies de mélange pour fiuides à sphères dures multi-composants. Les équations d'état proposées, combinées aux règles de mélange de Santos et al. et de Barrio-Solana, reproduisent les facteurs de compressibilité et les potentiels chimiques d'excès de façon plus précise que l'équation d'état de Boublik-Mansoori-Camahan-Starling-Leiand (BMCSL). Cependant, le RDF pair à la valeur de contact a des écarts plus grands que ceux obtenus avec l'équation d'état de BMCSL. La combinaison des équations proposées et la régle de mélange de Barrio-Solana donne une reproduction exacte du facteur de compressibilité pour des fluides de sphères dures binaires ayant un rapport de diamètre important m,me dans les régions de faible concentration de sphères les plus grandes. [source] Supplementation of dietary minerals during the early seawater phase increase vertebral strength and reduce the prevalence of vertebral deformities in fast-growing under-yearling Atlantic salmon (Salmo salar L.) smoltAQUACULTURE NUTRITION, Issue 4 2009P.G. FJELLDAL Abstract An earlier study demonstrated that under-yearling (0+) Atlantic salmon (Salmo salar L.) smolt had a lower vertebral mineral content and mechanical strength and higher prevalence of vertebral deformities than 1+ smolt during the early seawater (SW) phase. The present study aimed to examine if commercial extruded high-energy diets need to be supplemented additional minerals for proper bone mineralization and prevention of bone deformities in fast growing 0 + smolts. We studied vertebral morphology with radiology, and bone mineral content and mechanical strength in 60 g 0+ smolt fed diets with a normal (NM) or elevated (HM) bone mineral (P and Ca) contents from SW transfer (week 0) until 10 times weight increase at week 17. Thereafter, both groups were fed a commercial diet until a mean slaughter weight of 4100 g after 57 week. There were no differences in body weight and length between the dietary groups during the study, while the condition factor differed significantly at the final sampling (NM 1.40; HM 1.29). The most common bone deformity observed was compressions in the tail region of the vertebral column. Lower incidences of vertebral deformities (percent individuals with one or more deformed vertebrae) was observed in the HM group in week 17 (HM 20%; NM 47%) and week 57 (HM 37%; NM 73%), also reflected by higher vertebral length/dorso-ventral diameter ratio in weeks 17 (HM 0.99; MN 0.92) and 57 (HM 0.97; NM 0.88). The HM group had significantly higher vertebral mineral content (HM 550 g kg,1; NM 480 g kg,1) and mechanical strength (HM 9050 g mm,1; NM 4600 g mm,1) than the NM group after 8 week feeding. Plasma levels of Ca, P and D-vitamin metabolites recorded in week 8 reflected changes in P homeostasis, but could not explain the preventive effect of the HM diet on development of bone deformities. The results suggest that elevated dietary mineral content during the early SW phase may reduce the prevalence of vertebral deformities in fast growing 0 + salmon smolts. [source] Effect of two medicinal herbs (Astragalus radix and Lonicera japonica) on the growth performance and body composition of juvenile pikeperch [Sander lucioperca (L.)]AQUACULTURE RESEARCH, Issue 11 2008Zdzis, aw Zak Abstract The aim of this study was to determine the impact of feeding juvenile pikeperch diets with medicinal herb adjuvants on the growth performance, proximate body composition, fatty acids profile (whole fish, muscle tissues, viscera) and cytological and histological indicators of the liver and middle intestine. The fish (mean body weight of ca. 110 g) were fed diets with a 0.1% supplement of Astragalus radix (group A), Lonicera japonica (group L) or a mixture of these herbs (A. radix+L. japonica; group A/L) for 8 weeks. The herbal supplementation was not noted to have had an impact on the analysed indicators of fish growth performance, condition or feed conversion ratio (P>0.05). Statistically significant intergroup differences were noted in the value of the hepatosomatic index, hepatocyte size, their nucleus and nucleus/cytoplasm diameter ratio (P<0.05). Significant intergroup differences were also noted in the appearance of the hepatic parenchyma. Statistically significant intergroup differences were also noted in the protein content of the whole fish body. The analysis of the proximal composition of the fish viscera, in turn, indicated significant differences in the fat content (P<0.05). Among the analysed group of fatty acids (saturated , SFA, monoenoic , MUFA, polyenoic , PUFA) contained in the whole fish, the fillets and the viscera, significant intergroup differences were noted with regard to SFA (viscera) and MUFA (whole fish) (P<0.05). The total PUFA content was stable, although significant intergroup differences were noted with regard to a few of the acids that belong to this group (P<0.05). [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] Anthropometry of fetal vasculature in the chorionic plateJOURNAL OF ANATOMY, Issue 6 2007Z. Gordon Abstract Normal fetal development is dependent on adequate placental blood perfusion. The functional role of the placenta takes place mainly in the capillary system; however, ultrasound imaging of fetal blood flow is commonly performed on the umbilical artery, or on its first branches over the chorionic plate. The objective of this study was to evaluate the structural organization of the feto-placental vasculature of the chorionic plate. Casting of the placental vasculature was performed on 15 full-term placentas using a dental polymer mixed with colored ink. Observations of the cast models revealed that the branching architecture of the chorionic vessel is a combination of dichotomous and monopodial patterns, where the first two to three generations are always of a dichotomous nature. Analysis of the daughter-to-mother diameter ratios in the chorionic vessels provided a maximum in the range of 0.6,0.8 for the dichotomous branches, whereas in monopodial branches it was in the range of 0.1,0.3. Similar to previous studies, this study reveals that the vasculature architecture is mostly monopodial for the marginal cord insertion and mostly dichotomous for the central insertion. The more marginal the umbilical cord insertion is on the chorionic plate, the more monopodial branching patterns are created to compensate the dichotomous pattern deficiency to perfuse peripheral placental territories. [source] Fluid-particle drag in inertial polydisperse gas,solid suspensionsAICHE JOURNAL, Issue 8 2010William Holloway Abstract In this article, we extend the low Reynolds number fluid-particle drag relation proposed by Yin and Sundaresan for polydisperse systems to include the effect of moderate fluid inertia. The proposed model captures the fluid-particle drag results obtained from lattice-Boltzmann simulations of bidisperse and ternary suspensions at particle mixture Reynolds numbers ranging from 0 , Remix , 40, over a particle volume fraction range of 0.2 , , , 0.4, volume fraction ratios of 1 , ,i/,j , 3, and particle diameter ratios of 1 , di/dj , 2.5. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Migration and sedimentation of spherical particles in a yield stress fluid flowing in a horizontal cylindrical pipeAICHE JOURNAL, Issue 10 2009Othmane Merkak Abstract This study looks at the dynamics of a particle suspended in a viscoplastic fluid, flowing in a horizontal circular cylindrical pipe. Inertia effects are negligible in comparison with viscous effects and plastic effects. The suspensions are highly stabilized and at rest the spheres cannot settle under gravity alone. The results of Merkak et al. (AIChE J. 2008;54:1129,1138) are extended, taking into consideration both particles of the same density or denser than the fluid and pipe-to-particle diameter ratios of 8 or 56. New migration phenomena in the sheared zone are thus evidenced when buoyancy forces are nil. In the case of particles denser than the fluid, it is shown how the spheres settle by bypassing the plug-flow zone. A map showing the stability of flowing suspensions could, thus, be drawn. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Molecular simulation of complete phase diagrams for binary mixturesAICHE JOURNAL, Issue 7 2001Monica H. Lamm Vapor-liquid, vapor-solid and liquid-solid coexistence lines are calculated for binary mixtures of Lennard-Jones spheres using Monte Carlo simulation and the Gibbs-Duhem integration technique. Complete phase diagrams showing equilibrium between vapor, liquid and solid phases are constructed for binary Lennard-Jones mixtures with diameter ratios ranging from ,11 /,22 = 0.85,1.0 and attractive well-depth ratios ranging from ,11/,22 = 0.625,1.6, at a reduced pressure P*,P,/,11 = 0.002. The Lorentz-Berthelot combining rules are used to calculate the cross-species interaction parameters ,12 and ,12. The variation in the shape of the complete phase diagrams change as a function of the diameter ratio ,11 /,22 and well-depth ratio ,11 /,22 is systematically explored. The phase diagrams found here resemble those found experimentally for argon-methane, iodine-sulfur, water-sodium chloride, water-silver nitrate, water-potassium nitrate, and p-dichlorobenzene-p-dibromobenzene. [source] Swelling Behaviour of Isotropic Poly(n -butyl acrylate) Networks in Isotropic and Anisotropic SolventsMACROMOLECULAR SYMPOSIA, Issue 1 2008Boumédiène Dali Youcef Abstract Summary: The swelling properties of photochemically crosslinked poly(n -butyl acrylate) (PABu) networks in isotropic and anisotropic solvents were investigated experimentally. The purpose of this study was to examine the swelling kinetics of PABu networks in isotropic solvents and to compare the results obtained which those observed in the case of the low molecular weight liquid crystal 4-cyano-4,- n -pentyl-biphenyl known as 5CB. The phase diagrams were established in terms of composition and temperature for isotropic solvents, as toluene, acetone, cyclohexane, and methanol, and 5CB, using the plateau values corresponding to equilibrium states of swelling. The polymer networks were prepared via free radical polymerization/crosslinking processes by ultraviolet (UV) radiation of initial mixtures made up from a monomer, a crosslinker, and a photoinitiator. PABu networks with several crosslinking densities were formed using different quantities of difunctional monomer hexanedioldiacrylate (HDDA). Immersion of these networks in excess solvent allows measuring the solvent uptake by determination of the weight in isotropic solvents and diameter in an anisotropic solvent (5CB). Swelling data were rationalized by calculating weight and diameter ratios considering swollen to dry network states of the samples. [source] Study of particle trajectories, residence times and flow behavior in kneading discs of intermeshing co-rotating twin-screw extrudersPOLYMER ENGINEERING & SCIENCE, Issue 4 2004V. L. Bravo A three-dimensional finite element model was implemented for the solution of mass and momentum conservation equations in the kneading disc section of an intermeshing co-rotating twin-screw extruder. The polymer melt was modeled with a Carreau constitutive equation. The particle tracking technique was used to obtain residence times and analyze distributive mixing for different length to diameter ratios (L/D) of kneading discs. Previous studies from Kalyon et al. (1) and Cheng and Manas-Zloczower (2) have shown that the mixing performance of intermeshing co-rotating twin-screw extruders is highly dependent on the combination of screw configuration and operating conditions. The complexity of the geometry and the transient character of the flow demand powerful computational tools to characterize the flow and to develop a prediction tool for the analysis of relative performance between different configurations. Difficulties arise in the particle tracking technique because of the time discretization and the presence of moving boundaries. Results show the importance of particle history on the evaluation of the relative performance of different configurations of kneading blocks and suggest a reevaluation of the use of average flow characteristics for the analysis of mixing. Results also confirm the importance of an accurate description of the geometry and clearances in order to obtain information about relative mixing performance. Polym. Eng. Sci. 44:779,793, 2004. © 2004 Society of Plastics Engineers. [source] Stochastic Morphometric Model of the Balb/c Mouse LungTHE ANATOMICAL RECORD : ADVANCES IN INTEGRATIVE ANATOMY AND EVOLUTIONARY BIOLOGY, Issue 10 2010Pierre Madl Abstract The laboratory mouse is often used as a human surrogate in aerosol inhalation studies. Morphometric data on the tracheobronchial geometry of three in situ lung casts of the Balb/c mouse lung produced by the Air Pollution Health Effects Laboratory were analyzed in terms of probability density functions and correlations among the different airway parameters. The results of this statistical analysis reveal significant differences in diameters and branching angles between major and minor progeny branching off from the same parent airway at a given airway bifurcation. Number of bronchial airways generations along a given path, expressed by the termination probability, branching angles, and daughter-to-parent diameter ratios indicate that the location of an airway with defined linear airway dimensions within the lung is more appropriately identified by its diameter (or its parent diameter) than by an assigned generation number. We, therefore, recommend classifying the mouse lung airways by their diameters and not by generation numbers, consistent with our previous analysis of the rather monopodial structure of the rat lung (Koblinger et al., J Aerosol Med 1995;8:7,19; Koblinger and Hofmann, J Aerosol Med 1995;8:21,32). Because of lack of corresponding information on respiratory airways, a partly stochastic symmetric acinar airway model was attached to the tracheobronchial model, in which the number of acinar airways along a given path was randomly selected from a measured acinar volume distribution. The computed distributions of the geometric airway parameters and their correlations will be used for random pathway selection of inhaled particles in subsequent Monte Carlo deposition calculations. Anat Rec 293:1766,1786, 2010. © 2010 Wiley-Liss, Inc. [source] Destabilisation of homogeneous bubbly flow in an annular gap bubble columnTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 4 2010Fahd M. Al-Oufi Abstract Experimental results are presented to show that there are very significant differences in the mean gas void fractions measured in an open tube and a annular gap bubble column, when operated at the same gas superficial velocity, using a porous sparger. Measurements were carried out in a vertical 0.102,m internal diameter column, with a range of concentric inner tubes to form an annular gap, giving diameter ratios from 0.25 to 0.69; gas superficial velocities in the range 0.014,0.200,m/s were investigated. The mean gas void fraction decreases with increasing ratio of the inner to outer diameter of the annular gap column and the transition to heterogeneous flow occurs at lower gas superficial velocities and lower void fractions. Two reasons are proposed and validated by experimental investigations: (1) the presence of the inner tube causes large bubbles to form near the sparger, which destabilise the homogeneous bubbly flow and reduce the mean void fraction; this was confirmed by deliberately injecting large bubbles into a homogeneous dispersion of smaller bubbles, and (2) the shape of the void fraction profiles changes with gap geometry and this affects the distribution parameter in the drift-flux model. Both of these effects serve to reduce the mean gas void fraction in an annular gap bubble column compared to an open tube at the same gas superficial velocity. Des résultats expérimentaux sont présentés pour montrer qu'il existe de très grandes différences dans les fractions de vide gazeux moyennes mesurées dans un tube ouvert et une colonne à bulles à espace annulaire, lorsqu'ils sont utilisés à la même vitesse superficielle de gaz, au moyen d'un aérateur poreux. On a effectué des mesures dans une colonne verticale avec un diamètre interne de 0.102,m, avec une portée de tubes internes concentriques pour former un espace annulaire, procurant des rapports de diamètre de 0.25 à 0.69; des vitesses superficielles de gaz de 0.014 à 0.200,m/s ont été étudiées. La fraction de vide gazeux moyenne diminue avec le rapport croissant du diamètre interne à externe de la colonne à espace annulaire et la transition à la circulation hétérogène se produit à des vitesses superficielles de gaz et fractions de vide plus basses. Deux raisons sont proposées et validés par les vérifications expérimentales: (1) la présence du tube interne provoque la formation de grandes bulles près de l'aérateur, ce qui déstabilize l'écoulement à bulles homogène et réduit la fraction de vide moyenne; cet état a été confirmé en injectant délibérément de grandes bulles dans une dispersion homogène de plus petites bulles et, (2) la forme des profils de fraction de vide change avec la géométrie de l'espace qui les sépare, ce qui a des conséquences sur le paramètre de distribution du modèle à flux de dérive. Ces deux effets servent à réduire la fraction de vide gazeux moyenne dans une colonne à bulles à espace annulaire, en comparaison avec un tube ouvert à la même vitesse superficielle de gaz. [source] Improved design of mantle tanks for small low flow SDHW systemsINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 12 2006Simon Furbo Abstract Side-by-side tests of two small low flow solar domestic hot water (SDHW) systems based on mantle tanks have been carried out under the same test conditions in a laboratory test facility. The systems are identical with exception of the mantle tanks. One of the mantle tanks has the mantle inlet port located at the top of the mantle and the other mantle tank has the mantle inlet port moved 0.175 m down from the top of the mantle. The thermal performance is almost the same for the two systems in the measuring period of 252 days. The solar fractions were 0.66 and 0.68 for the two systems. The tests showed also that the system with the low mantle inlet perform better than the system with the high mantle inlet in periods with low solar fractions, that is in less sunny periods. Further, calculations with a simulation model for low flow SDHW systems based on mantle tanks showed that mantle tanks currently marketed can be greatly improved by relatively simple design changes: increasing the height/diameter ratio, reducing the mantle height and increasing the insulation thickness on the sides of the tank. Copyright © 2006 John Wiley & Sons, Ltd. [source] Reactive grafting of glycidyl methacrylate onto polypropyleneJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2010Emma-Louise Burton Abstract This work explored the melt-phase grafting of glycidyl methacrylate (GMA) onto polypropylene on a closely intermeshing corotating twin-screw extruder (16-mm screws, 40 : 1 length/diameter ratio). The modification of the base polypropylene to produce GMA-grafted polypropylene was achieved via peroxide-induced hydrogen abstraction from the polypropylene followed by the grafting of the GMA monomer or by the grafting of styrene followed by copolymerization with the GMA. In this study, both the position and order of the reactant addition were investigated as a route to improving graft yields and reducing side reactions (degradation). For the peroxide,GMA system, adding GMA to the melt before the peroxide resulted in significant improvements in the graft levels because of the improved dispersion of GMA in the melt. The addition of a comonomer (styrene) was explored as a second route to improving the graft yield. Although the addition of the comonomer led to a considerable rise in the level of grafted GMA, altering the order of the reactant addition was not found to contribute to an increase in the grafted GMA levels. However, variable levels of grafted styrene were achieved, and this may play an important role in the development of grafted polymers to suit specific needs. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Polymer- and wax-based monoconcentrate predispersed pigments in the colouring of plasticsCOLORATION TECHNOLOGY, Issue 4 2010Suresh P Deshmukh Over the past few decades, masterbatch production has been increasing year by year. Pigments are used primarily in masterbatches because of their ability to impart colour or opacity to a matrix. The effectiveness of pigments depends not only on their intrinsic ability to absorb or scatter light, but also, importantly, on the dispersiblity and distribution of the pigments that can be achieved in plastics. Nowadays, stringent environmental as well as excellent quality controls are making inevitable the use of non-dusty monoconcentrated predispersed pigments for the production of masterbatches for the colouring of plastics. Commercially, for the most part, two types of monoconcentrated predispersed pigments are being used for the colouring of thermoplastic masterbatches. These are polymer- and wax-based predispersed pigments. This study has been undertaken to provide a comparison of the colouring properties of polymer- and wax-based monoconcentrated predispersed pigments. Four commercially used organic pigments have been selected. Both types of monoconcentrate predispersed pigments have been developed on a co-rotating twin-screw compounding extruder with a length/diameter ratio of 44. A detailed analysis on the comparison of the colouring properties is presented. Results indicate that good colour properties are achieved when operating conditions are optimised. [source] | |||||||||||||||||||||||||