1,721,147 research outputs found
A comparison of growth, gas exchange and productivity in Olea europaea cultivars growing on Maditerranean hills
No full textThis work concern the ecophysiology of olive cultivars growing on Mediterranean hills. Our aim was to qauntify the photosynthetic efficiency of the cultivars in cultivation. In two hill aresa, we tested the phenological and ecophysiological variability of olive cultivars grown on non-irrigated land, with different pedo-climatic characteristics
Effetti dell'applicazione fogliare di glicinbetaina e chitosano su Puccinellia distans (Jacq.) Parl. sottoposta a stress salino
No full textSome morphological, anatomical, physiological responses of different olive cultivars to high temperatures and drought stress
No full textThe aim of this work is to find relationships between morphology and physiology in three different olive cultivars: Biancolilla, Cerasuola and Nocellara del Belice, when plants were subjected to high temperature and drought. These cultivars are estensively used in Sicily for productive purposes. The results about ultrastructural and physiological studies on shoot growth, leaf anatomy, chloroplast ultrastructure and oxygen production, indicate that Biancolilla is the cultivar in which the studied traits showed fewer changes and can be considered to have the best tolerance to both high temperatures and water deficit. In the other hand, the morphological and physiological characteristics studied are more affected by thermal and drought stress in Nocellara del Belice than in the other two cultivars
CFD simulation of particle distribution in stirred vessels
No full textIn this work the particle concentration distribution in two-phase stirred tanks is simulated on the basis of information on the three-dimensional flow field, as obtained by numerical solution of the flow equations (CFD) using the well known k - ε turbulence model. Two modelling approaches are attempted. In the simpler method the flow field is first simulated neglecting the influence of the solid phase; on the basis of the resulting flow field a very simple sedimentation model is employed for solving the solids mass balance equations in order to compute the particle concentration field. In this case no inertial effects on the solid particles are considered, so that the convective and diffusional exchanges for the solid phase are assumed to coincide with those for the liquid phase. In the more advanced approach the momentum balance equations for both the solid and liquid phases are simultaneously solved. Experimental data on the axial profiles of particle concentration have been obtained in a laboratory scale agitated tank. The experimental technique utilized is non intrusive being based on light attenuation measurements and is also able to provide information at high particle concentrations. The comparison of experimental data with simulation results is satisfactory with both simulation approaches. Differences between the two approaches concerning their accuracy and computational effort are discussed. The need to make a suitable estimate of the particle drag coefficients in turbulent fluid media is emphasized
CFD simulation of gas-liquid stirred vessels
No full textComputational 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 limited effect on flow fields as well as on total gas hold-up and ia distribution in the vessel space.
This result implies that coalescencelbreakage dynamics computations may be conveniently carried out off-line after having assessed the vessel flow field, with large savings of co~nputational demand
Free surface oxygen transfer in large aspect ratio unbaffled bio-reactors, with or without draft-tube
Full text linkIt is widely accepted that animal cell damage in aerated bioreactors is mainly related to the bursting of bubbles at the air-liquid interface. A viable alternative to sparged bioreactors may be represented by uncovered unbaffled stirred tanks, which have been recently found to be able to provide sufficient mass transfer through the deep free surface vortex which takes place under agitation conditions. As a matter of fact, if the vortex is not allowed to reach impeller blades, no bubble formation and subsequent bursting at the free-surface, along with relevant cells damage, occurs.In this work oxygen transfer performance of large aspect ratio unbaffled stirred bioreactors, either equipped or not with an internal draft tube, is presented, in view of their use as biochemical reactors especially suited for shear sensitive cell cultivation
Oxygen transfer performance of unbaffled stirred vessels in view of their use as biochemical reactors for animal cell growth
No full textCultivation of microorganisms, plants or animal cells requires liquid agitation in order to ensure oxygen and nutrient transfer and to maintain cell suspension. However, In such suspensions both mechanical agitation and sparging aeration can cause cell death. Many studies on animal cell damage due to mechanical agitation and sparging aeration have shown that mechanical damage of freely suspended animal cells is in most cases associated with bursting bubbles at the air–liquid interface (Barrett et al., 2010, Nienow et al., 1996).
Gas bubbles are usually generated by direct air sparging to propagate oxygen in a culture suspension. Mechanical agitation may also introduce gas bubbles to the culture fluid through vortexing entrainment from the free surface.
In this work oxygen transfer performance of an unbaffled stirred vessel is presented in view of its use as biochemical reactor for animal cell growth. As a matter of fact, oxygen mass transfer can occur through the free surface deep vortex which takes place when agitation is started. If this is not allowed to reach impeller blades, bubble formation and subsequent bursting inside the reactor is avoided.
Experimental results showed that this kind of bioreactor can provide sufficient oxygen mass transfer for animal cell growth, so resulting in a valid alternative to more common sparged reactors
Reattore per la precipitazione di micro e nano-particelle
No full textReattore di precipitazione a due cilindri concentrici a meato sottile e ingressi multipli contrapposti e/o a stella, che consente di ottenere elevata riproducibilità delle dimensioni finali delle particelle prodotte, con particolare riguardo alle nanoparticelle.
Tale reattore presenta un notevole potenziale nell’ambito delle nanotecnologie, in settori industriali quali la produzione di adesivi, di pigmenti, di catalizzatori, e la produzione di nano-particelle farmacologicamente attive con la possibilità di inglobare il principio attivo in "nano-carriers" funzionalizzati, al fine di eseguire un rilascio controllato del principio attivo, preferenzialmente nelle adiacenze del bersaglio desiderato
Influence of Viscosity on Mass Transfer Performance of Unbaffled Stirred Vessels
No full textUnbaffled stirred tanks are seldom employed in the process industry as they are considered poorer mixers than baffled vessels. However they may be expected to provide significant advantages in a wide range of applications (e.g. crystallization, food and pharmaceutical processes, etc) where the presence of baffles is often undesirable. Moreover, in plants or animal cell cultivation bioreactors, where cell damage is often caused by bursting bubbles at the air –medium interface (Barret et al., 2010), they can provide sufficient mass transfer through the free surface vortex, so bubble formation and subsequent bursting inside the reactor can be conveniently avoided (Scargiali et al., 2012).
In this work the influence of viscosity on oxygen transfer performance of an unbaffled stirred vessel is investigated in view of its use as a biochemical reactor for animal cell growth.
Liquid viscosity was increased by adding weighted amounts of polyvinylpyrrolidone (PVP) to distilled water. Experimental results show that at rotational speeds lower than the critical one (Ncrit , at which the free surface vortex reaches the impeller), despite the absence of gas dispersion inside the reactor and relevant cell damage due to bubble bursting, gas-liquid mass transfer is not adversely affected by viscosity and the systems remains able to provide sufficient oxygen for typical animal cell cultures. At rotational speeds higher than Ncrit air entrapment and dispersion occurs inside the reactor and an increase of mass transfer performance is observed while increasing viscosity, probably due to smaller bubble coalescence rates due in turn to the viscosity increase itself as well as to gas-liquid interface modifications by PVP
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