Search results for "gas-liquid"
showing 10 items of 19 documents
International descriptive and interventional survey for oxycholesterol determination by gas- and liquid-chromatographic methods
2018
International audience; Increasing numbers of laboratories develop new methods based on gas-liquid and high-performance liquid chromatography to determine serum concentrations of oxygenated cholesterol metabolites such as 7alpha-, 24(S)-, and 27-hydroxycholesterol. We initiated a first international descriptive oxycholesterol (OCS) survey in 2013 and a second interventional survey 2014 in order to compare levels of OCS reported by different laboratories and to define possible sources of analytical errors. In 2013 a set of two lyophilized serum pools (A and B) was sent to nine laboratories in different countries for OCS measurement utilizing their own standard stock solutions. In 2014 eleven…
Modelling and Simulation of Gas–liquid Hydrodynamics in a Rectangular Air-lift Reactor
2013
Abstract Computational Fluid Dynamics is a quite well established tool for carrying out realistic simulations of process apparatuses. However, as a difference from single phase systems, for multiphase systems the development of CFD models is still in progress. Among the two-phase systems, gas–liquid systems are characterised by an additional complexity level, related to the fact that bubble sizes are not known in advance, being rather the result of formation and breakage-coalescence dynamics and therefore of complex phenomena related to flow dynamics and interfacial effects. In the present work, Euler–Euler Reynolds-averaged flow simulations of an air-lift reactor are reported. All bubbles …
Bubble formation at variously inclined nozzles
2014
Bubble formation at variously inclined submerged nozzles, fed with a continuous gas flow rate, is investigated. Results confirm previous findings, such as a substantial independence of bubble size of nozzle diameter and its dependence on the cubic root of gas flow rate at sufficiently high values of this parameter. Nozzle inclination in the range between 0 and 135° from the vertical upward orientation is found to have a negligible effect on bubble size. Observed bubble rise velocities lead to an estimation of the average liquid velocity induced by bubbles motion, leading in turn to a very simple correlation for the estimation of the liquid velocities induced by the repeated passage of bubbl…
Simplified dynamic pressure method for kLa measurement in aerated bioreactors
2010
Abstract A simplified version of the dynamic pressure method for measuring mass-transfer coefficients in gas–liquid systems is proposed. With this method oxygen concentration in the liquid phase is monitored after a sudden change of total pressure is applied to the system. With respect to the original technique introduced by Linek [14] the simplified version here proposed greatly simplifies the data treatment, yet resulting in good accuracy for most practical purposes. In practice, with the help of a simple mathematical model, it is found that the dynamic oxygen concentration response, when plotted as residual driving force versus time in a semi-log diagram, should be expected to finally se…
Gas-liquid-solid Operation of a High Aspect Ratio Self-ingesting Reactor
2012
Gas-liquid stirred vessels are widely employed to carry out chemical reactions involving a gas reagent and a liquid phase. The usual way for introducing the gas stream into the liquid phase is through suitable distributors placed below the impeller. An interesting alternative is that of using “self ingesting” vessels where the headspace gas phase is injected and dispersed into the vessel through suitable surface vortices. In this work the performance of a Long Draft Tube Self-ingesting Reactor (LDTSR) dealing with three-phase (gas-liquid-solid) systems, is investigated. Preliminary experimental results on the effectiveness of this contactor for particle suspension and gas-liquid mass transf…
Mass transfer and hydrodinamic characteristics of a high aspect ratio self-ingesting reactor for gas-liquid operations
2007
Abstract The mass transfer performance of a gas–liquid self-ingesting stirred reactor is reported both for coalescing and non-coalescing systems. The vessel features are a high aspect ratio and a rather narrow multiple-impeller draft tube, through which the gas phase is ingested and led down to the vessel bottom, where it is finely dispersed into the liquid rising in the annular portion of the vessel. Comparison is made between k L a values determined by several variants of the dynamic method, among which pure oxygen absorption in a previously de-gassed liquid phase. Results show that the gas–liquid mass transfer coefficient values obtained with the last approach are remarkably larger than …
Caratterizzazione del pattern lipidico e degli acidi grassi del muscolo dell’ibrido Acipenser naccarii (Bonaparte, 1836) x A. baerii (Brandt, 1869) e…
2002
Muscle phospholipids and tryglicerides were measured in two sturgeon (Acipenseridae) hybrids. Fatty acid composition of the two lipidic fractions showed a strong similarity between the two hybrids.
CFD simulation of gas-liquid stirred vessels
2006
Computational Fluid Dynamics is an increasingly important tool for carrying out realistic simulations of process apparatuses. As a difference from single phase systems, for multipliase systcms the development of CFD models is still at its early stages. In the present work CFD simulations of gasliquid stirred tanks are reported. All bubbles are assumed to share the same size, and a simplified approach is adopted for the description of momentum exchanges between tile two phases. In particular ir is shown that the only parameter needed for modeling drag forces is bubble terminal velocity. Results show that in a quite wide range encompassing most practical applications, bubble size has a limite…
Local gas-liquid hold-up and interfacial area via light sheet and image analysis
2010
Particle Image Velocimetry techniques coupled with advanced Image Processing tools are receiving an increasing interest for measuring flow quantities and local bubble-size distributions in gas-liquid contactors. In this work, an effective experimental technique for measuring local gas hold-up and interfacial area, as well as bubble size distribution, is discussed. The technique, hereafter referred to as Laser Induced Fluorescence with Shadow Analysis for Bubble Sizing (LIF-SABS) is based on laser sheet illumination of the gas-liquid dispersion and synchronized camera, i.e. on equipment typically available within PIV set-ups. The liquid phase is made fluorescent by a suitable dye, and an opt…
A NOVEL TECHNIQUE FOR MEASURING LOCAL BUBBLE SIZE DISTRIBUTION
2009
A novel experimental technique for measuring the local gas hold-up and the statistical distribution of local bubble size, is proposed. The technique is based on laser sheet illumination of the gas-liquid dispersion and synchronized camera, i.e. on equipment typically available in PIV set-ups. The liquid phase is made fluorescent by a suitable dye, and a band-pass optical filter is placed in front of the camera optics, in order to allow only fluoresced light to reach the camera CCD. In this way bubbles intercepted by the laser sheet are clearly identified thanks to the neat shade resulting in the images. This allows excluding from subsequent analysis all bubbles visible in the images but not…