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Small Bubbles (small + bubble)
Selected Abstracts2145: Descemet´s membrane detachment 16 years after PK and 10 months after phacoACTA OPHTHALMOLOGICA, Issue 2010JO FERNANDEZ MENDY Purpose The purpose of this paper is to present an unusual case of DMD and analyze this complication Methods A 57-year-old woman, who had bilateral keratoconus, underwent three penetrating keratoplasties (PK) on her RE in 1981, 1993 and 1995 resulting in ptisis bulbi. In her LE she underwent two PK (1981, 1994) follow by arcuate incisions (1995) and an uneventful phacoemulsification in 2007. 10 months after cataract surgery, she begun with blurred vision, the BCVA was 20/400 and was seen by 3 ophthalmologists who made the diagnosis of endothelial failure and suggested a new PK or a DSAEK. We performed an Optical Coherence Tomography, diagnosing a complete Descemet´s membrane detachment (DMD). An intracameral gas injection of C3F8 at 16% was performed in the operating room, and the patient was instructed to maintain a supine position. After 24 hours VA improved to 20/80 and after 72 hours 20/30 UCVA. A small bubble was present in the anterior chamber for more than 3 weeks. One month later she achieved 20/20 with Contact Lens. During the first year after reattachment it was necessary to change the CL due to an increasing with the rule astigmatism from 3D to 5D. Results Two years after gas injection BSVA is 20/25 because she is no longer using CL, Descemet´s membrane still remains well attached, even thought we realized that there was a trend to steepen the vertical meridian due to the widening of a nasal arcuate incision, that we think was the origin of the DMD. Conclusion DMD is a rare complication of Phacoemulsification, seen immediately after the surgery. So far there has not reported any complete DMD after phaco after PK. We think that it is mandatory to perform a corneal OCT in all cases of PK and stromal edema; it could probably be a DMD. [source] Study of the production of hydrogen bubbles at low current densities for electroflotation processesJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 10 2010Carlos Jiménez Abstract BACKGROUND: Flotation processes are widely used in waste-water treatment and it is quite important to have a tool to determine and optimize the size distribution of the bubbles produced. In this work, the electrochemical production of bubbles to enhance the performance of electrocoagulation processes by flotation is studied. To do this, a current density range characteristic of electrocoagulation processes is used to produce microbubbles (<5 mA cm,2), instead of the higher values used in other studies to characterize electroflotation in non-combined processes. RESULTS: Current density and pH were found to influence the process significantly. In the range used, higher current densities allow a larger number of small size bubbles to be obtained, appropriate for use in electroflotation processes. However, at the boundaries of the range, the size of the bubbles was increased advising against use. Neutral pH values also favour the formation of small bubbles, and the presence of possible competing reactions have to be considered because they diminish the gas flow and affect the number of bubbles and their size. The roughness of the surface of the electrode material also has an important influence. CONCLUSIONS: The image acquisition and analysis system developed allows measurement of the size distribution of hydrogen bubbles in the range of current densities studied. Current density and pH seem to be the main parameters affecting the mean diameter of bubbles and the amount of gas produced, and the electrode material may also influence hydrogen production significantly. Copyright © 2010 Society of Chemical Industry [source] Simulation of a slurry-bubble column reactor for Fischer-Tropsch synthesis using single-event microkineticsAICHE JOURNAL, Issue 8 2009Gisela Lozano-Blanco Abstract A single-event microkinetic model for Fischer-Tropsch synthesis including the water-gas shift reaction has been implemented in a one-dimensional, two-bubble class, heterogeneous model with axial effective diffusion to study the performance of a commercial slurry bubble column reactor. Mass balance equations are solved for every species in the reaction network in the large bubbles, small bubbles, and slurry phase, whereas the energy balance is applied to the slurry phase. The catalyst concentration profile is described by a sedimentation-dispersion model. The combination of microkinetics that generate net production rates for the individual reaction products and hydrodynamics allows describing detailed concentration profiles along the reactor axis as a function of operating conditions and design parameters. As example, the effects of catalyst loading, syngas feed flow rate, inlet temperature, or hydrogen to carbon monoxide inlet ratio on the individual hydrocarbons are investigated. To our knowledge, no reactor model in literature is able to describe detailed compositions at the level described by the reactor model developed in this work. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Studies on Liquid,Gas and Three-Phase Fluidized Beds with Pulsating Air FlowsTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 1 2003Christopher G. J. Baker Abstract The effects of air-flow pulsation and water and air flowrates on the hydrodynamics of liquid,gas and three-phase fluidized beds containing 3-mm glass beads have been studied in a 90-mm i.d. column. Under steady-flow conditions, both types of bed contained a relatively large number of small bubbles. With a pulsing air flow, however, a smaller number of much larger bubbles or slugs were formed. This was attributed to different mechanisms of bubble formation at the distributor. Variations in phase holdup were explained in terms of the effects of the operating parameters on the bubble characteristics. On a étudié dans une colonne de 90 mm de diamètre intérieur les effets de la pulsation air-écoulement et des débits d'eau et d'air sur l' hydrodynamique de lits fluidisés gaz,liquide et triphasiques contenant des billes de verre de 3 mm. Dans des conditions d'écoulement en régime permanent, les deux types de lit contenaient un nombre relativement important de petites bulles. Toutefois, avec un écoulement à air pulsé, il s 'est formé un moins grand nombre de bulles de très grande dimension ou de bouchons. Ceci est imputable aux différents mécanismes de formation des bulles au niveau du distributeur. Les variations dans la rétention des phases sont expliquées par les effets des paramètres opératoires sur les caractéristiques des bulles. [source] VOF-Simulation of the Lift Force for Single Bubbles in a Simple Shear FlowCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 9 2006D. Bothe Abstract Bubbles in shear flows experience a lift force, causing them to migrate sideways while they are rising. This lateral migration is investigated in numerical simulations, which are carried out with an extended version of the highly parallelized code FS3D, employing an advanced Volume-of-Fluid method. The movement of single bubbles in linear shear flows is simulated to obtain the magnitude of the lift force , expressed by the lift force coefficient CL , for various bubble diameters and material data. Simulation results are in good agreement with experiments for medium liquid phase viscosities. An investigation of the dynamic pressure on the bubble surface explains why large bubbles migrate in the opposite direction compared to small bubbles. [source] | ||||||||||