Search results for "impianti chimici"

Free-surface shape in unbaffled stirred vessels: Experimental study via digital image analysis

2013

There is a growing interest in using unbaffled stirred tanks for addressing a number of processing needs such as low shear damage (sensitive biocultures), low attrition (solid–liquid applications), deep-cleaning/sterilization (pharmaceutical applications). The main feature of uncovered, unbaffled stirred tanks is highly swirling motion of the fluid that results in a deformation of the free liquid surface. At sufficiently high agitation speeds the resulting whirlpool reaches the impeller and gives rise to a gas–liquid dispersion, so leading to the formation of a dispersion without the use of gas-sparger; the so-called self-inducing operation of the vessel. In this work, digital image analysi…

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…

Free surface oxygen transfer in large aspect ratio unbaffled bio-reactors, with or without draft-tube

2015

Abstract It 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 e…

Coupling of electromembrane processes with reverse osmosis for seawater desalination: Pilot plant demonstration and testing

2022

Reverse osmosis (RO) is the most widespread technology to produce drinking water from seawater (SW). However, the integration of different membrane processes offers interesting alternatives. In this work, electromembrane processes were integrated with RO to desalinate real seawater in a pilot plant with 25 m3/day capacity. Electrodialysis (ED, either two-stage or single stage), shortcut reverse electrodialysis (scRED) and assisted reverse electrodialysis (ARED) pre-desalinated seawater before RO with the ED-ED-RO, ED-RO, and scRED-ARED-RO process schemes. Treated wastewater was used as salt sink in the scRED-ARED tests. The performance of the pilot plant can be summarized as follows: water …

Experimental investigation of the effects of efficiency promoters in a MSF lab-scale unit

2006

Modelling Nannochloropsis gaditana Growth in Reactors with Different Geometries, Determination of Kinetic Parameters and Biochemical Analysis in Resp…

2022

Microalgae are unicellular and photosynthetic microorganisms which grow thanks to inorganic salts, CO2 and light, and find applications in several fields thanks to their variety. The industrial application of microalgae has not often been fully exploited because of a lack of information about how microalgae respond to inputs and to different growth environments. In the present work a model able to predict the microalgae growth in reactors with different geometries was developed. We combined a Monod-like model for the specific growth rate with the Lambert-Beer law of homogeneous light distribution in thick photobioreactors. Kinetic parameters related to the cultivation of the microalga Nanno…

A geometric approach for predicting vertical stationary profiles of weakly inertial advecting-diffusing particles in closed incompressible flows

2004

Abstract Mixing of weakly inertial particles in closed flows is often addressed by considering individual particles as passive advecting-diffusing tracers, subjected to an additional settling velocity resulting from body forces (e.g. gravity). We show that the qualitative and quantitative features of the vertical particle distribution (i.e. the horizontal cross-sectional averages of particle concentration) can be predicted from the structure of the flow resulting from the superposition of the stirring field and the settling velocity. The prediction is based upon the observation that the resulting flow can be divided into two nonoverlapping regions, namely trajectories that are confined with…

Influence of bundle porosity on shell-side hydrodynamics and mass transfer in regular fiber arrays: A computational study

2023

CFD predictions of the effects of a fiber bundle porosity on shell-side hydrodynamics and mass transfer under conditions of steady laminar flow were obtained. Fluid was assumed to flow around regular hexag-onal or square arrays of cylindrical fibers of different pitch to diameter ratios, yielding bundle porosities ranging from the theoretical minimum up to similar to 1. A large number of axial, transverse and mixed flow combinations were simulated by letting the axial and transverse flow Reynolds numbers and the trans-verse flow attack angle vary. Both fully developed and developing conditions (entrance effects) were con-sidered. The continuity and momentum equations, along with a transport…

Turbulent Fluid Flow in Closed- and Free-Surface Unbaffled Tanks Stirred by Radial Impellers

1996

Scale-up and viscosity effects on gas–liquid mass transfer rates in unbaffled stirred tanks

2018

Abstract The interest in the process industry on unbaffled stirred tanks has greatly expanded in the last years because they may bring about significant advantages in a number of applications, including biochemical, food and pharmaceutical processes where the presence of baffles is undesirable for several reasons. Despite their application potential, unbaffled vessels still lack fundamental information, due to the fact that only recently their capabilities have started being dug out. The lack of information on scale up effects is possibly the main reason hindering practical applications. In this work the influence of vessel size and liquid viscosity on the mass transfer performance in unbaf…