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Complex Flow Pattern (complex + flow_pattern)
Selected AbstractsCondensation of steam in the presence of air on a single tube and a tube bankINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 4 2003Adrian Briggs Abstract Data are presented for condensation of steam in cross-flow with and without the presence of air on the outside of a single tube and a bank of tubes. The tube bank consisted of ten staggered rows of two and one tubes per row. For pure steam the experimental results for both the single tube and tube bank gave good agreement with single-tube theory when account was taken of the reduction in vapour velocity due to condensation. There was some evidence, however, that condensate inundation may play a minor role in reducing heat-transfer coefficients on the lower tubes in the bank. For the case of condensation from steam,air mixtures, the single-tube data gave good agreement with theory. For condensation from steam,air mixtures on the bank of tubes, the data were significantly under predicted by single-tube theory, possibly because of mixing and re-circulation due to the complex flow pattern around the tubes. Copyright © 2003 John Wiley & Sons, Ltd. [source] Cohesive-driven particle circulation in the solids conveying zone of a single-screw extruderADVANCES IN POLYMER TECHNOLOGY, Issue 2 2008Michael R. Thompson Abstract Aspects of heat transfer within the solids conveying zone of a single-screw extruder were studied by using a specially constructed drum testing apparatus. Experiments were conducted with linear low-density polyethylene, polystyrene (PS), and polypropylene (PP) samples by examining their transient temperature profile while the heated drum was stationary or moving. In accordance with classic solids conveying theory, the granular beds of PP and PS remained as plugs while the drum rotated. In such cases, the dominant modes of heat transfer for these systems are conduction through the contact area of a particle and conduction through the interstitial gas. An exception to this behavior was found with PE, in which the bed temperature increased more rapidly while the drum rotated. Visual observations of the bed showed that the particles circulated in the presence of shear and that this complex flow pattern increased in velocity as the drum temperature approached the onset temperature for melting the PE material. With strong correlation between the rate of circulation and the temperature rise in the bed, the movement of particles was assumed to act in a convective heat transfer mode bringing about more uniform heating of the polymer. The circulation phenomenon was attributed to dominant adhesive forces at the particle,drum interface overcoming the cohesive strength of the bulk. © 2009 Wiley Periodicals, Inc. Adv Polym Techn 27:74,88, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20121 [source] Three-dimensional simulation of planar contraction viscoelastic flow by penalty finite element methodINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 7 2010Yue Mu Abstract The planar contraction flow is a benchmark problem for the numerical investigation of viscoelastic flow. The mathematical model of three-dimensional viscoelastic fluids flow is established and the numerical simulation of its planar contraction flow is conducted by using the penalty finite element method with a differential Phan-Thien,Tanner constitutive model. The discrete elastic viscous split stress formulation in cooperating with the inconsistent streamline upwind scheme is employed to improve the computation stability. The distributions of velocity and stress obtained by simulation are compared with that of Quinzani's experimental results detected by laser,doppler velocimetry and flow-induced birefringence technologies. It shows that the numerical results agree well with the experimental results. The numerical methods proposed in the study can be well used to predict complex flow patterns of viscoelastic fluids. Copyright © 2009 John Wiley & Sons, Ltd. [source] Computational Fluid Dynamics Analysis of Blade Tip Clearances on Hemodynamic Performance and Blood Damage in a Centrifugal Ventricular Assist DeviceARTIFICIAL ORGANS, Issue 5 2010Jingchun Wu Abstract An important challenge facing the design of turbodynamic ventricular assist devices (VADs) intended for long-term support is the optimization of the flow path geometry to maximize hydraulic performance while minimizing shear-stress-induced hemolysis and thrombosis. For unshrouded centrifugal, mixed-flow and axial-flow blood pumps, the complex flow patterns within the blade tip clearance between the lengthwise upper surface of the rotating impeller blades and the stationary pump housing have a dramatic effect on both the hydrodynamic performance and the blood damage production. Detailed computational fluid dynamics (CFD) analyses were performed in this study to investigate such flow behavior in blade tip clearance region for a centrifugal blood pump representing a scaled-up version of a prototype pediatric VAD. Nominal flow conditions were analyzed at a flow rate of 2.5 L/min and rotor speed of 3000 rpm with three blade tip clearances of 50, 100, and 200 µm. CFD simulations predicted a decrease in the averaged tip leakage flow rate and an increase in pump head and axial thrust with decreasing blade tip clearances from 200 to 50 µm. The predicted hemolysis, however, exhibited a unimodal relationship, having a minimum at 100 µm compared to 50 µm and 200 µm. Experimental data corroborate these predictions. Detailed flow patterns observed in this study revealed interesting fluid dynamic features associated with the blade tip clearances, such as the generation and dissipation of tip leakage vortex and its interaction with the primary flow in the blade-blade passages. Quantitative calculations suggested the existence of an optimal blade tip clearance by which hydraulic efficiency can be maximized and hemolysis minimized. [source] | ||||||||||