Search results for "multiphase"
showing 10 items of 43 documents
Measurement techniques and modelling of multiphase systems.
2011
Multiphase systems are often encountered in process industry. Widely diffused applications and operations involve the contact between different phases (gas-solid, gasliquid, solid liquid, etc.) for different purposes, such as chemical reactions of physical operations (heat transfer, mass transfer). Multiphase flows are therefore one of the most frequent applied fields in chemical engineering. The present thesis is aimed at the development of experimental techniques for the investigation of multiphase flow in general, with particular focus on the analysis of gas-solid and gas-liquid systems. Notably, the development of image analysis techniques is the central thread of the present contributi…
Power Consumption in Uncovered Unbaffled Stirred Tanks: Influence of the Viscosity and Flow Regime
2013
Notwithstanding the increasing industrial interest toward unbaffled tanks, available experimental information on their behavior is still scant, even for basic quantities such as the mechanical power drawn. In this work, the influence of the Reynolds and Froude numbers on the power consumption characteristics is presented for unbaffled stirred tanks operating both in nonaerated conditions (subcritical regime) and in aerated conditions (supercritical regime), i.e., when the free surface vortex has reached the impeller and the gas phase is ingested and dispersed inside the reactor. Experimental results obtained at various liquid viscosities show that power numbers obtained in subcritical condi…
CFD MODELLING OF PARTICLE SUSPENSION IN STIRRED TANKS
2011
Mixing of solid particles into liquids in mechanically agitated vessels is a topic of primary importance for several industrial applications. A great deal of research efforts has been devoted so far to the assessment of the minimum impeller speed (Njs) able to guarantee that all particles are suspended. Conversely, only little attention has been paid to the evaluation of the amount of solid particles that are suspended at impeller speeds N lower than Njs, despite the fact that in a number of industrial applications agitation speeds smaller than Njs are actually adopted [1,2]. The present work deals with dense solid-liquid partial suspensions in baffled stirred tanks and particularly focuses…
Oxygen Transfer Performances of Unbaffled Bio_Reactors with Various Aspect Ratios
2014
Cultivation of microorganisms, plants or animal cells requires liquid agitation in order to ensure oxygen and nutrient transfer and to maintain cell suspension. 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). Gas bubbles are usually generated by direct air sparging aimed at supplying oxygen to the culture medium. Mechanical agitation may also introduce gas bubbles in the culture medium via vortexing entrainment from the free surface. In this work oxygen transfer performance of an unbaffle…
Analysis of the hydrodynamics of a periodically operated trickle-bed reactor—A shock wave velocity
2014
Abstract The relationship describing the shock wave velocity was formulated for the trickle-bed reactor operating at periodically changed feeding the bed with liquid phase. The values of shock wave velocity calculated from derived equations were compared with experimental values obtained for both fast and slow mode of base–pulse periodic liquid feeding and using liquids differing in physicochemical properties. A good agreement between these two sets of values of shock wave velocity was obtained. It has to be emphasized that the relationship (Eq. (26) ) derived in this study enables to estimate the values of the shock wave velocity when only mean values of variables of a process are known.
Macroscopic capillarity without a constitutive capillary pressure function
2006
This paper challenges the foundations of the macroscopic capillary pressure concept. The capillary pressure function, as it is traditionally assumed in the constitutive theory of two-phase immiscible displacement in porous media, relates the pressure difference between nonwetting and wetting fluid to the saturation of the wetting fluid. The traditional capillary pressure function neglects the fundamental difference between percolating and nonpercolating fluid regions as first emphasized in R. Hilfer [Macroscopic equations of motion for two phase flow in porous media, Phys. Rev. E 58 (1998) 2090]. The theoretical approach proposed here starts from residual saturations as the volume fractions…
Dynamic performance evaluation of a non linear digital control technique for multiphase VRMs
2010
On the measurement of local gas hold-up, interfacial area and bubble size distribution in gas–liquid contactors via light sheet and image analysis: I…
2013
Abstract In this work a novel experimental technique for measuring local gas hold-up, interfacial area and bubble size distribution, in gas–liquid systems is proposed. The technique is based on advanced Image Processing coupled with experimental set-ups typically available for Particle Image Velocimetry. A fluorescent dye dissolved in the liquid phase allows to identify in-plane bubbles among all visible bubbles in the images. To this end, a suitable algorithm is proposed. The raw data so obtained are processed by previously developed statistical methods that result in a reliable reconstruction of actual dispersion properties. The technique is applied to the case of a gas-dispersed mechanic…
On the bubbling dynamics of binary mixtures of powders in 2D gas-solid fluidized beds
2012
Abstract The bubbling behavior of fluidized beds has been thoroughly investigated in the last decades by means of several techniques (e.g. X-ray, Inductance, Resistance and Impedance based techniques). In recent years, Digital Image Analysis Techniques have shown their potential for accurate and cost effective measurements. Most of the works related to the experimental analysis of bubble behavior in the field of gas-solid fluidization actually deal with monodispersed particles although almost all industrial equipments operate with mixtures of particles. Among the works available in literature dealing with mixtures of particles having different diameters and/or densities, most of them aim at…