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Geometrical Configuration (geometrical + configuration)
Selected AbstractsComputation of heat transfer enhancement in a plate-fin heat exchanger with triangular inserts and delta wing vortex generatorINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 9 2010Gulshan Sachdeva Abstract Longitudinal vortices disrupt the growth of the thermal boundary layer, thereby the vortex generators producing the longitudinal vortices are well known for the enhancement of heat transfer in compact heat exchangers. The present investigation determines the heat transfer characteristics with secondary flow analysis in plate fin triangular ducts with delta wing vortex generators. This geometrical configuration is investigated for various angles of attack of the wing i.e. 15°, 20°, 26° and 37° and Reynolds numbers 100 and 200. The constant wall temperature boundary condition is used. The solution of the complete Navier Stokes equation and the energy equation is carried out using the staggered grid arrangement. The performance of the combination of triangular secondary fins and delta wing with stamping on slant surfaces has also been studied. Copyright © 2009 John Wiley & Sons, Ltd. [source] Flow of Newtonian and power law liquids in tube bundlesTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 5 2009U. K. Singh Abstract In this work, the annular (tangential) flow of Newtonian and non-Newtonian fluids in tube bundles has been studied experimentally. Extensive pressure drop data has been obtained embracing wide ranges of the Reynolds number (13,6600) and for two test modules of different geometrical arrangements, but of similar overall void fraction. Preliminary experiments suggest that the pressure drop is mainly determined by the overall void fraction of the bundle and is relatively insensitive to the detailed geometrical configuration of the bundle. A simple predictive correlation has been developed which reconciles the present results for Newtonian and power law fluids with acceptable levels of reliability. Dans le cadre de ces travaux, on a examiné de façon expérimentale l'écoulement annulaire (tangentiel) des fluides newtoniens et non newtoniens dans des faisceaux tubulaires. On a obtenu de nombreuses données de chute de pression englobant de vastes plages du nombre de Reynolds (13-6600), et pour deux modules d'essai de différentes dispositions géométriques, mais à taux de vide global similaire. Les expériences préliminaires suggèrent que la chute de pression est déterminée principalement par le taux de vide global du faisceau et est relativement insensible à la configuration géométrique détaillée du faisceau. La création d'une simple corrélation prédictive a permis de rapprocher les présents résultats pour les fluides newtoniens et des fluides en loi de puissance avec des niveaux acceptables de fiabilité. [source] Numerical Comparative Study on the Hemodynamic Performance of a New Helical Graft With Noncircular Cross Section and SwirlGraftARTIFICIAL ORGANS, Issue 1 2010Anqiang Sun Abstract The helically distributed ribbons of thrombus, formed in the commercially available SwirlGraft (Veryan Medical, London, UK), are the result of its wall shear stress distribution, which has zonary areas of low wall shear stress. In order to overcome the inherent deficiency of the SwirlGraft, a new helical graft with a noncircular cross section was proposed and compared numerically with the SwirlGraft in terms of wall shear stress distribution, helicity of the swirling flow created, and pressure drop over the grafts. The numerical results showed that due to the modification to the geometrical configuration of the SwirlGraft, wall shear stress in the new helical graft model was enhanced, and the zones of low wall shear stress existing in the SwirlGraft were completely eliminated. The present numerical study also predicted a slightly steeper pressure drop and reduction in helicity in the new helical graft model in comparison with the SwirlGraft model. Based on the study, we believe that the new helical graft with a noncircular cross section may reduce the possibility of acute thrombus formation in the graft because the enhanced wall shear stress can impede the stay and adherence of platelets and leukocytes to the surface of the graft. [source] Density Functional Theory (DFT) studies on the ground state of NO3(2A,2) radical and the first triplet state of NO3+cationCHINESE JOURNAL OF CHEMISTRY, Issue 3 2000Cao Xiao-Yan Abstract Density Functional Theory (DFT) studies on the ground states (2A,2) of NO3 radical and on die ground state (1A,;1) and the first triplet state (3E,) of NO3+ cation provide an unambiguous prediction about their geometrical structure: the ground states of both NO3 radical and NO3+ cation have D3h symmetry and the geometrical configuration of me first triplet state 3E, of NO3+ cation has C2v symmetry. It is shown that as for as the ionization energy calculations on NO3 radical are concerned, the results are only slightly different, no mater that gradient corrections of the exchange-correlation energy are included during self-consistent iterations or they are included as perturbations after the self-consistent iterations. [source] Simulations of grafting monomers and associated degradation of polypropylene in a modular co-rotating twin screw extruderJOURNAL OF VINYL & ADDITIVE TECHNOLOGY, Issue 4 2005Jongmin Keum Kinetic models of grafting maleic anhydride (MAH) and methyl methacrylate (MMA) on polypropylene (PP) were developed for screw extrusion. However, the kinetic models were insufficient to explain the grafting reactions along the length of modular co-rotating twin screw extruders because the rheological properties and the residence time of PP changed owing to degradation of PP during the grafting reaction. In order to model this system for a modular co-rotating twin screw extruder, the kinetic model of grafting reaction and models for degradation of PP were combined with fluid mechanics and heat transfer. Given the geometrical configurations of the screw, the operating conditions, and the physical properties of the polypropylene, the simulations predicted variation of molecular weight and mean residence time due to degradation of PP. The weight percent of grafted MAH or MMA on PP profiles along the screw axis was also calculated in the simulation. These predictions were compared with experimental data for various operating conditions. J. VINYL. ADDIT. TECHNOL. 11:143,149, 2005. © 2005 Society of Plastics Engineers. [source] Third and fourth Stokes parameters in polarimetric passive microwave remote sensing of rough surfaces over layered mediaMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 12 2008Leung Tsang Abstract We consider the four Stokes parameters in microwave emission from a layered medium with the top interface being a rough surface. The rough surface varies in one horizontal direction so that azimuthal asymmetry exists in the 3-D problem. Dyadic Green's functions of multilayered media are used to formulate the surface integral equations. Periodic boundary conditions are used. The numerical results show that the presence of the layered media below the rough surface reduces the vertical and horizontal brightness temperatures. The interaction between the rough surface and the layered media also enhance the third and fourth Stokes parameters. In particular, the fourth Stokes parameter can be large for such geometrical configurations. Results show that the nonzero third and fourth Stokes parameters exist for all frequencies and are particularly large when the rough surface has large slope. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 3063,3069, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23892 [source] Mixing mechanism of three-tip kneading block in twin screw extrudersPOLYMER ENGINEERING & SCIENCE, Issue 1 2000Makoto Yoshinaga In recent years, twin screw extruders have been applied to various kinds of polymer processing. It has been important to find their optimum geometrical configurations and operational processing conditions for the best performance of extrusions and products. Many engineers have been evolving numerical and the experimental methods to characterize the mixing performance for twin screw extruders. We have carried out three-dimensional flow simulations of kneading blocks in intermeshing co-rotating twin screw extruders by using the finite element method to quantify their ability in distributive and dispersive mixing. We discuss their performance in distributive mixing for three different type of kneading blocks in terms of the residence time distribution and the nearest distance between markers at various periods of time, by using the marker tracking method. Those numerical techniques and applications of mixing indices have enabled us to quantify and evaluate their abilities in distributive mixing of kneading blocks in twin screw extruders. [source] A new photobioreactor for continuous microalgal production in hatcheries based on external-loop airlift and swirling flowBIOTECHNOLOGY & BIOENGINEERING, Issue 1 2009Karine Loubière Abstract This study deals with the scale of a new photobioreactor for continuous microalgal production in hatcheries. The combination of the state-of-art with the constraints inherent to hatcheries has turned the design into a closed, artificially illuminated and external-loop airlift configuration based on a succession of elementary modules, each one being composed of two transparent vertical interconnected columns. The liquid circulation is ensured pneumatically (air injections) with respect to a swirling motion (tangential inlets). A single module of the whole photobioreactor was built-up to scale its geometry (diameter and length) and to optimize its design (air sparger, tangential inlets). The volumetric productivities were predicted by modeling radiative transfer and growth of Isochrysis affinis galbana (clone Tahiti). The hydrodynamics of the liquid phase was modeled in terms of global flow behavior (circulation and mixing times, Péclet number) and of swirling motion decay along the column (Particle Image Velocimetry). The aeration performances were determined by overall volumetric mass transfer measurements. Continuous cultures of Isochrysis affinis galbana (clone Tahiti) were run in two geometrical configurations, generating either an axial or a swirling flow. Lastly, the definitive options of design are presented as well as a 120-L prototype, currently implemented in a French mollusk hatchery and commercialized. Biotechnol. Bioeng. 2009;102: 132,147. © 2008 Wiley Periodicals, Inc. [source] | ||||||||||||||||