Abstract
This project deals with the characterization of structured fluids, which are adopted in the preparation and processing of many products in different industrial applications, ranging from pharmaceutics to personal care and emulsifications, to name a few. The investigation is based on a multiscale approach, combining experiments and simulations on binary mixtures of water and Pluronic in a laboratory stirred reactor. Various mixture concentrations are considered at different temperature, thus leading to different microstructures of Pluronic molecules in water, which in turn significantly affect the fluid rheology. The UNIBO research unit specific task is concerned with a detailed experimental study, mainly based on Stereo Particle Image Velocimetry data, carried out with the final purpose of providing insight into the prevailing flow regimes, the spatial variations of the velocity and the shear rate in the reactor volume. The energy requirement expected in the industrial operations as a function of the impeller speed is obtained from the power consumption measured by a strain gauge system. Steady state and transient conditions during the mixture preparation are considered, starting from completely separated phases up to the complete homogenization of the mixture. The experimental investigation complements the rheological characterization of the mixtures and provides data for the validation of Computational Fluid Dynamics models. Achieved Results The contribution of the UNIBO unit has provided insight into the reactor performances and data for model validation. A detailed experimental investigation based on Stereo Particle Image Velocimetry (SPIV) and power consumption measurements was carried out for identifying the flow regimes, the spatial variations of the flow field, the local shear rate and the energy consumption in a stirred reactor. The geometrical configuration was selected based on the expected wide range of local viscosities due to the different microstructures of Pluronic molecules in the mixtures. Pure Pluronics were considered first, then the variation of the fluid dynamics characteristics was observed at variable composition and temperature of the mixtures. Steady state and transient experiments were performed. The energy requirement expected in the industrial operations was obtained from the torque measured by a strain gauge system on the impeller shaft. The power consumption time traces revealed the characteristic time for the achievement of the complete homogenization starting from separated phases and the additional energy requirement during the preparation with respect to steady state operations. The SPIV data have provided details on the flow field and the shear rate distribution as a function of the mixture rheology. The velocity components depending on the Pluronic mixture composition show different magnitude. The fluid axial recirculation decreases moving from laminar towards turbulent conditions and the radial velocity component is significant just in the impeller discharge stream for any regime. The flow field exhibits marked variations with impeller Reynolds number of about 104, at higher values the typical independency of the dimensionless flow field from impeller tip speed is achieved. The shear rate maps obtained from the instantaneous velocity data confirm that due to the significant heterogeneity in the stirred tank the adoption of a single average value for the whole vessel is not appropriate and the three dimensionality of the flow must be taken into account, thus making the planar measurements quite unsuitable for quantitative measurements. Based on the flow characteristics estimated from SPIV data, useful guidelines for the spatial discretization of computational domain in CFD calculations were obtained. Overall, the experimental results have provided information on the interplay between the reactor geometrical characteristics and the fluids rheology and their effect on the hydrodynamics, thus contributing to the development of modelling methods aimed at improving reactors scale-up.
Dettagli del progetto
Responsabile scientifico: Giuseppina Montante
Strutture Unibo coinvolte:
Dipartimento di Chimica Industriale "Toso Montanari"
Coordinatore:
Politecnico di TORINO(Italy)
Contributo totale Unibo: Euro (EUR) 50.775,00
Durata del progetto in mesi: 24
Data di inizio
28/09/2023
Data di fine:
27/09/2025
