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Capillary Number (capillary + number)
Selected AbstractsMobility of shear thinning viscous drops in a shear Newtonian carrying flow using DR-BEMINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 12 2009M. Giraldo Abstract The study of drop behaviour has attracted great interest in the last years due to its importance in different industrial and biological systems. Most available works focus on Newtonian drops, excluding some very important applications such as polymer mixing. Simulations of non-Newtonian drops have had only limited study, mostly in time-dependent rheologies or simple flow cases. This work presents a boundary-only formulation based on the dual reciprocity method to model the motion and deformation of non-Newtonian shear thinning drops due to a shear Newtonian unbounded carrying flow. Pair-wise interactions at low Reynolds number between two viscous shear thinning non-Newtonian drops are numerically simulated in order to obtain mobility magnitudes under linear shear flow of different strengths. Separation of the drops in the direction perpendicular to the imposed flow field at high capillary number (small surface tension) and low viscosity ratio was favoured by shear thinning, increasing in magnitude as the capillary number increases and the viscous ratio decreases. Higher values of this separation occur at higher values of the viscosity ratio when compared with the case of Newtonian drops. In order to obtain a good physical description of the non-Newtonian drop behaviour, while maintaining good computational performance, the non-Newtonian viscosity is made to obey the truncated power law model. Copyright © 2008 John Wiley & Sons, Ltd. [source] Formation of Arrayed Droplets by Soft Lithography and Two-Phase Fluid Flow, and Application in Protein Crystallization,ADVANCED MATERIALS, Issue 15 2004B. Zheng Abstract This paper presents an overview of our recent work on the use of soft lithography and two-phase fluid flow to form arrays of droplets. The crucial issues in the formation of stable arrays of droplets and alternating droplets of two sets of aqueous solutions include the geometry of the microchannels, the capillary number, and the water fraction of the system. Glass capillaries could be coupled to the PDMS microchannels and droplets could be transferred into glass capillaries for long-term storage. The arrays of droplets have been applied to screen the conditions for protein crystallization with microbatch and vapor diffusion techniques. [source] Viscous co-current downward Taylor flow in a square mini-channelAICHE JOURNAL, Issue 7 2010Özge Keskin Abstract This article presents a computational study of the co-current downward Taylor flow of gas bubbles in a viscous liquid within a square channel of 1 mm hydraulic diameter. The three-dimensional numerical simulations are performed with an in-house computer code, which is based on the volume-of-fluid method with interface reconstruction. The computed (always axi-symmetric) bubble shapes are validated by experimental flow visualizations for varying capillary number. The evaluation of the numerical results for a series of simulations reveals the dependence of the bubble diameter and the interfacial area per unit volume on the capillary number. Correlations between bubble velocity and total superficial velocity are also provided. The present results are useful to estimate the values of the bubble diameter, the liquid film thickness and the interfacial area per unit volume from given values of the gas and liquid superficial velocities. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Snap-off of a liquid drop immersed in another liquid flowing through a constricted capillaryAICHE JOURNAL, Issue 8 2009T. J. Peña Abstract Emulsions are encountered at different stages of oil production processes, often impacting many aspects of oilfield operations. Emulsions may form as oil and water come in contact inside the reservoir rock, valves, pumps, and other equipments. Snap-off is a possible mechanism to explain emulsion formation in two-phase flow in porous media. Quartz capillary tubes with a constriction (pore neck) served to analyze snap-off of long ("infinite") oil droplets as a function of capillary number and oil-water viscosity ratio. The flow of large oil drops through the constriction and the drop break-up process were visualized using an optical microscope. Snap-off occurrence was mapped as a function of flow parameters. High oil viscosity suppresses the breakup process, whereas snap-up was always observed at low dispersed-phase viscosity. At moderate viscosity oil/water ratio, snap-off was observed only at low capillary number. Mechanistic explanations based on competing forces in the liquid phases were proposed. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Characterization of dynamical emulsification process in concentrated conditionsAICHE JOURNAL, Issue 8 2007Christophe Baravian Abstract Emulsification at constant shear rate in concentrated conditions (50% in volume fraction) is investigated experimentally by measuring simultaneously the droplet size and the global shear stress using a specially designed rheo-optical "Steady Light Transport" apparatus. The capillary number is varied by changing the continuous phase viscosity, corresponding to disperse to continuous phase viscosity ratios between 0.02 and 2. We show that when the capillary number is large enough (>0.35), emulsification occurs. At constant shear rate, this time-dependant process can be separated into four steps: (1) flow start-up, (2) premix formation, (3) a progressive reduction in droplet size, associated with an increase in shear stress, (4) changes in droplet size and shear stress stop at a well-defined emulsification time. Step (3), called dynamical emulsification, is fully controlled by the critical capillary number and the mechanism of drop size reduction stops when viscous dissipation dominates the droplet elongation and break-up mechanism. This approach accurately describes both the variation in shear stress with droplet size during Stage (3) and the final state of the emulsion in terms of droplet size and viscosity. © 2007 American Institute of Chemical Engineers AIChE J, 2007 [source] Investigation of unsaturated flow in woven, braided and stitched fiber mats during mold-filling in resin transfer moldingPOLYMER COMPOSITES, Issue 4 2001J. Slade In Resin Transfer Molding (RPM), which is a process to manufacture polymer composites, the impregnation of fibrous reinforcement In the form of mats by a thermosetting resin is modeled as the flow of a Newtonian liquid through a single length-scale porous medium. While this approach is sufficiently accurate for random fiber-mats, it can lead to appreciable errors when applied to woven, braided, or stitched fiber-mats that contain two length scales. This work investigates the primary factors governing the isothermal unsaturated flow through such dual-scale porous media. Two studies were conducted to better understand this phenomenon: the first experimenatally investigated the flow, while the second theoretically modeled the flow and identified important parameters affecting such a flow with the help of dimensionless analysis. In the first study, one-dimensional constant injection rate experiments were performed using various fiber mats. The unsaturated flow behavior of various mats was characterized using a constant "sink" term in the continuity equation. Results indicated that for a given fiber-mat, the magnitude of the sink effect was a function of the capillary number. In the second study, a numerical model was developed to describe flow through dual-scale preforms in which the two flow domains, the inter- and intra-tow regions, were coupled. We identified a dimensionless number called the sink effect index , that characterizes the magnitude of liquid absorption by the tows and is a function of the relative resistance to flow in the tow and inter-tow regions, and the packing density of the tows. The parametric study of this index with the help of numerical simulations reveals its influence on the flow and identifies the distinct transient and steady-state flow regimes. [source] Meniscus deformation and dynamics of moving contact line between poly(ethylene terephthalate) surface and glycerol,water mixturesASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 2 2009Dr Stoyan I. Karakashev Abstract The microscopic hydrodynamic (HD) and macroscopic theories for describing the meniscus deformation and dynamics of a moving contact line have been analyzed and compared by using the extrapolated dynamic contact angles between a poly(ethylene terephthalate) (PET) surface and glycerol,water mixtures. The analysis showed that the microscopic theory is confined by the microscopic length scale and small capillary number. The macroscopic theory is not subjected to any restrictions. Three (inner, intermediate and outer) regions of the dynamic meniscus have been combined by using the contact molecular kinetics and hydrodynamics. The combined molecular-HD theory has been validated using the experimental data for the extrapolated dynamic contact angles between a PET surface and glycerol,water mixtures. The analysis showed that the combined theory describes the phenomenon of wetting qualitatively. It was found that the contradiction within the theoretical framework of the molecular kinetics and hydrodynamics hinders the exact description of the wetting phenomenon. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Numerical Study on Bubble Formation of a Gas-Liquid Flow in a T-Junction MicrochannelCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 12 2009L. Dai Abstract Bubble emergence in a gas-liquid flow in a T-junction microchannel of 100,,m diameter, operated under a squeezing regime, was simulated with the computational fluid dynamics method. In general, bubble formation in channels includes three stages: expansion, collapse and pinching off. After analyzing and comparing quantitatively the three forces of pressure, surface tension and shear stress acting on the gas thread in the whole process, their effects in the different stages were identified. The collapse stage was the most important for bubble formation and was investigated in detail. It was found that the collapse process was mostly influenced by the liquid superficial velocity, and the rate and time of collapse can be correlated with empirical equations including the liquid superficial velocity, the capillary number and the Reynolds number. [source] Capillary Filling Flows inside Patterned-Surface MicrochannelsCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 6 2006W. Huang Abstract Capillary flows inside microchannels with patterned-surfaces are investigated theoretically and numerically. The surface energy method is used to derive an equivalent contact angle (ECA) model for small capillary number flows. The SIMPLE algorithm using a volume of fluid (VOF) method is adopted to investigate the flows in those microchannels. The flow characteristics such as the liquid front shapes and the evolution of the liquid lengths are obtained. The numerical results reveal that capillary flows in a patterned-surface microchannel still follow the traditional capillary theories. The ECA model is confirmed by the numerical results. It indicates that the capillary flows inside the patterned-surface microchannels can be estimated by means of the homogeneous-surface microchannels with the equivalent contact angle. The ECA model provides a good criterion for the total wettability of a patterned-surface microchannel, as well. [source] Myocardial growth before and after birth: clinical implications,ACTA PAEDIATRICA, Issue 2 2000AM Rudolph Perinatal changes in myocardial growth have recently evoked considerable interest with regard to cardiac chamber development with congenital cardiac lesions and to myocardial development in preterm infants. It is suggested that cardiac chamber development is influenced by blood flow. Experimental pulmonary stenosis in fetal lambs may induce either greatly reduced or markedly increased right ventricular volume. Ventricular enlargement appears to be associated with a large ventricular volume load resulting from tricuspid valve regurgitation. A small competent tricuspid valve is associated with reduced flow through the ventricle due to outflow obstruction and a small right ventricle. Postnatal growth of the ventricles in congenital heart disease is discussed. Increase in myocardial mass prenatally is achieved by hyperplasia, both during normal development and when myocardial mass is increased by right ventricular outflow obstruction. Postnatally, increases in myocardial mass with normal growth, as well as with ventricular outflow obstruction, are largely due to hypertrophy of myocytes. Myocardial capillary numbers do not increase in proportion with myocyte numbers in ventricular myocardium in association with outflow obstruction. The postnatal effects of these changes in congenital heart lesions are considered. Studies in fetal lambs suggest that the late gestational increase in blood cortisol concentrations is responsible for the change in the pattern of myocardial growth after birth. The concern is raised that prenatal exposure of the premature infant to glucocorticoids, administered to the mother to attempt to prevent hyaline membrane disease in the infant, may inhibit myocyte proliferation and result in a heart with fewer than normal myocytes. This would necessitate that each myocyte would have to hypertrophy abnormally to achieve a normal cardiac mass postnatally. [source] | |||||||||||||