Search results for "STIR"

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…

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…

Control of a Non-isothermal CSTR by Type-2 Fuzzy Logic Controllers

2009

The paper describes the application of a type-2 fuzzy logic controller (FLC) to a non-isothermal continuous stirred tank reactor (CSTR) characterized by the presence of saddle node and Hopf bifurcations. Its performance is compared with a type-1 fuzzy logic controller performance. A full analysis of the uncontrolled CSTR dynamic was carried out and used for the feedback-feedforward fuzzy controllers development. Simulation results confirm the effectiveness and the robustness of the type-2 FLCs which outperform their type-1 counterparts, particularly when uncertainties are present in the system.

Numerical prediction of flow fields in baffled stirred vessels: A comparison of alternative modelling approaches

1998

Abstract Numerical simulations of the flow field in baffled mixing tanks, based on three alternative methods, are presented and discussed. In the first method, the impeller is not explicitly simulated, and its effects are modelled by imposing suitable, empirically derived, boundary conditions to the external flow. In the second method, the whole vessel volume is divided into two concentric, partially overlapping, regions. In the inner region, containing the impeller, the flow field is simulated in the rotating reference frame of the latter, while in the outer region simulations are conducted in the reference frame of the laboratory. Information is iteratively exchanged between the two regio…

An integrated approach for the HCl and metals recovery from waste pickling solutions: pilot plant and design operations

2021

Abstract Continuous regeneration of industrial pickling solutions and recovery of valuable materials are implemented in a pilot-scale plant including diffusion dialysis (DD), where HCl is recovered, membrane distillation (MD), where HCl is concentrated, and reactive precipitation (CSTR), where metal ions are recovered in different forms. The integration of the three processes allows to minimize waste streams generation and to accomplish a closed-loop process, thus increasing the environmental sustainability and economic impact of the galvanizing industry. Process reliability was proved through the operation of a demonstrator in the real industrial environment of the Tecnozinco SrL hot-dip g…

Control of a non-isothermal continuous stirred tank reactor by a feedback–feedforward structure using type-2 fuzzy logic controllers

2011

A control system that uses type-2 fuzzy logic controllers (FLC) is proposed for the control of a non-isothermal continuous stirred tank reactor (CSTR), where a first order irreversible reaction occurs and that is characterized by the presence of bifurcations. Bifurcations due to parameter variations can bring the reactor to instability or create new working conditions which although stable are unacceptable. An extensive analysis of the uncontrolled CSTR dynamics was carried out and used for the choice of the control configuration and the development of controllers. In addition to a feedback controller, the introduction of a feedforward control loop was required to maintain effective control…

Modelling Turbulent Inter-Phase Drag in Mechanically Stirred Solid-Liquid Suspensions

2012

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…