Solid distribution and mixing time in stirred tanks: The case of floating particles

Abstract

This work concerns floating particle distribution and liquid mixing dynamics in a solid‐liquid stirred tank. Measurements of local solids concentration distribution at steady‐state conditions and of liquid homogenization in the presence of dispersed particles at transient conditions are collected with up‐pumping and down‐pumping pitched blade turbines. Electrical resistance tomography is the selected experimental technique for the data acquisition in the opaque solid‐liquid mixture. For the time dependent conductivity data processing, the same method commonly applied to the mixing time determination from planar laser induced fluorescence measurements is considered. The method is successfully extended to the characterization of liquid mixing with floating particles. The local data obtained by the ERT technique over the whole vessel volume are fully exploited. The robustness of the method for tackling conductivity variations close to the liquid free surface and due to the particles movement is assessed.

Particles dissolution and liquid mixing dynamics by Electrical Resistance Tomography

“…In Figure 3, the threshold CoV norm value of 0.02 suggested by Paglianti et al (2017a) for the identification of the achievement of the liquid homogenization conditions in slurry stirred tanks is also depicted. The curves shown in Figure 3 highlight that the characteristic time required for the liquid homogenization in the tank is weakly dependent on the particle size.…”

“…To this end, the values of the local variables estimated in each single pixel are considered. The pixels that fulfil a specific criterion are summed up cumulatively, extending the approach already devised in a previous investigation concerning the suspension of solid particles in stirred vessels (Paglianti et al, 2017a(Paglianti et al, , 2017b. Specifically, when the normalized local conductivity, x i , is considered, the pixel is assumed to be well mixed using a threshold x of 60.1.…”

“…Different variables are considered and compared for the determination of the liquid mixing time and the solid-liquid mass transfer time and for observing their variations as a function of the size of the dissolved solids. The limitations of the section averaged conductivity evaluations and the problems associated with the disturbances due to the inert solids fluctuations affecting the local conductivity data were discussed elsewhere (Paglianti et al, 2017a).…”

“…So far, ERT was applied to the investigation of stirred tanks to measure the solid concentration in dense suspensions (e.g. Carletti et al 2014;Hosseini et al, 2010;Lassaigne et al, 2016), the effects of solids in gas-liquid stirred tanks (Cooke et al, 2008), the liquid homogenization time using a passive tracer (Carletti et al, 2016;Paglianti et al, 2017a, Sardeshpande et al, 2016 and the liquid homogenization in case of floating particles (Paglianti et al, 2017b). To the best of our knowledge, this is the first investigation addressing particles dissolution in dense solid-liquid stirred tanks based on ERT data, with the partial exception of the work of Shirhatti et al (2005).…”

Large blade impeller application for turbulent liquid–liquid and solid–liquid mixing

“…The measurements were performed using the ITS 2000 ERT instrumentation (Industrial Tomography Systems Ltd.), which was already adopted for the dispersed phase concentration distribution and the liquid mixing time measurements in two‐phase vessels stirred with fast impellers (e.g., in the work of Paglianti et al [ 18 ] ). The measurements were based on the injection of electric current from an adjacent electrode pair at a time and on the measurement of the voltage difference from the remaining pairs of electrodes.…”