Search results for "FLE"
showing 10 items of 3517 documents
INFLUENZA SUL COMPORTAMENTO DINAMICO DI UN ROTORE SOSPESO ATTRAVERSO CUSCINETTI MAGNETICI ATTIVI MEDIANTE μ-SYNTHESIS E LOOP-SHAPING DESIGN
2011
In questo lavoro viene effettuato un confronto sul comportamento dinamico di un albero rotante quando è sospeso attraverso un sistema di due cuscinetti magnetici ciascuno costituito da due assi. Le sospensione magnetica attiva è ottenuta elaborando due diversi sistemi di controllo che realizzano la stabilità del rotore conferendo a quest’ultimo delle prestazioni robuste nel mantenimento degli spostamenti entro certi margini prestabiliti. Ognuno di questi sistemi di controllo è caratterizzato da otto ingressi e quattro uscite con la presenza di incertezze sul guadagno spostamento e guadagno di corrente; ciò è giustificato dal semplice fatto che gli apparati elettronici possono usurarsi con i…
MIXING TIME IN UNBAFFLED STIRRED TANKS
2012
Unbaffled stirred tanks, despite their poorer mixing performance with respect to baffled vessels, are gaining a growing industrial interest as they provide significant advantages in selected applications, including a number of biochemical, food and pharmaceutical processes. There still is however a general lack of information on their mixing performance, that needs to be addressed in order to fully exploit their application potential. The present work is aimed at providing experimental information on mixing rates in an unbaffled vessel operated without top-cover (Uncovered Unbaffled Stirred Tank, UUST). The planar laser induced fluorescence (PLIF) technique was adopted for measuring the dis…
POWER CONSUMPTION IN UNBAFFLED TANKS: SUB AND SUPER-CRITICAL REGIMES
2013
Unbaffled stirred tanks are increasingly recognized as a viable alternative to common baffled tanks for a range of processes (e.g. crystallization, food and pharmaceutical processes, etc) where the presence of baffles is undesirable for some reason. Also, in the case of bioreactors for animal cell cultivation, where cell damage is mainly related to bubbles bursts at the air –liquid interface, unbaffled tanks have been shown to be able to provide sufficient mass transfer through the free surface vortex. As a consequence bubble formation and subsequent bursting is conveniently avoided (Scargiali et al., 2012). The same feature clearly makes unbaffled vessels potentially advantageous for any f…
CFD simulation of radially stirred baffled and unbaffled tanks
2019
Stirred tanks typically employed in process industries are provided with baffles. Although the presence of baffles is known to guarantee good mixing rates, unbaffled vessels may be compulsory in some applications as crystallization, bioremediation, biotechnology and ore industry. A better understanding of unbaffled stirred vessels flow dynamics may allow (i) a proper design to be performed and (i) conditions/processes where baffle presence can be avoided to be recognized. In the present study, the k-ω SST was used to simulate an unbaffled tank from early to fully turbulent regime (Re≈600-33,000). The unbaffled tank simulated has a diameter T=0.19m and is stirred by a standard six-bladed Rus…
Particle Suspension in Vortexing Unbaffled Stirred Tanks
2016
Three-phase processes in which particle suspension has to be achieved in conjunction with gas dispersion are traditionally carried out in sparged, baffled stirred tanks. The operation of such tanks can suffer, however, from particles tending to block the sparger holes. A viable alternative might be provided by uncovered unbaffled stirred tanks (UUSTs), where gas self-injection can occur when the free-surface vortex reaches the impeller blades and gas bubbles begin to be ingested by the liquid. In this work, the particle suspension and liquid aeration performances in three-phase UUSTs were experimentally investigated and compared with relevant literature correlations concerning baffled syste…
A 2-D model of electrodialysis stacks including the effects of membrane deformation
2021
Abstract Membrane-based processes have gained a relevant role in many engineering applications. Much effort has been devoted to thoroughly understand the fundamental phenomena behind them. However, membrane deformation has been taken into consideration only recently, although much evidence has shown its impacts in many applications. This work presents a novel 2-D, multi-scale, semi-empirical process model able to predict the behavior and the performance of Electrodialysis (ED) systems in cross-flow configurations in the presence and absence of local membrane deformations. The model exploits the results and the simulation approaches of previous fluid-structure investigations performed by the…
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…
Dynamic response of equivalent orthotropic plate model for stiffened plate: numerical-experimental assessment
2017
Abstract Over the last two decades, homogenization-based modeling techniques have attracted considerable attention. In fact, through these methods, structures such as corrugated or stiffened plates, commonly referred to as structurally orthotropic plates, can be approximately studied as equivalent flat plates with orthotropic behavior. Specifically, these homogenization techniques allow for the direct determination of the equivalent flexural and torsional rigidities which appear in the governing equation for the deflection of the equivalent orthotropic plate. It is worth noting that, the determined equivalent material properties retain the dependence on the geometric parameters of the origi…
SIMULAZIONI CFD DEL CAMPO DI MOTO A BASSO NUMERO DI REYNOLDS IN BIOREATTORI AGITATI CON E SENZA SETTI FRANGIVORTICE
2016
I recipienti meccanicamente agitati sono apparecchiature frequenti dell’industria chimica di processo. Questi sono tipicamente dotati di setti frangivortice (recipienti baffled) atti a rompere il moto prettamente tangenziale tipico dei recipienti sprovvisti di setti (recipienti unbaffled) e convertirlo in moto assiale e radiale. La presenza dei setti evita inoltre nella zona centrale del sistema la formazione del vortice d’aria che può talvolta essere indesiderato o in taluni casi creare instabilità una volta arrivato alla girante. I recipienti unbaffled sono considerati quindi dei miscelatori meno efficienti rispetto a quelli provvisti di setti. Tali sistemi sono pertanto ad oggi impiegati…
Electrodialysis for water desalination: A critical assessment of recent developments on process fundamentals, models and applications
2018
Abstract The need for unconventional sources of fresh water is pushing a fast development of desalination technologies, which proved to be able to face and solve the problem of water scarcity in many dry areas of the planet. Membrane desalination technologies are nowadays leading the market and, among these, electrodialysis (ED) plays an important role, especially for brackish water desalination, thanks to its robustness, extreme flexibility and broad range of applications. In fact, many ED-related processes have been presented, based on the use of Ion Exchange Membranes (IEMs), which are significantly boosting the development of ED-related technologies. This paper presents the fundamentals…