Electrical resistance tomography-assisted analysis of dispersed phase hold-up in a gas-inducing mechanically stirred vessel

Tomographic analysis of the hydrodynamic attributes of the gas–liquid–solid mixing in a 1-l capacity stirred-tank equipped with a 4-blade gas-entrainment impeller has been used to obtain the dispersed phase hold-up distribution as a function of stirring speed (impeller Reynolds Number, ReI) and solid particle loading. Although the liquid phase stirring was turbulent, both gas and solid flows went through different hydrodynamic regimes and experienced radial hold-up gradient over the range of impeller speed employed. Global solid phase hold-up profile exhibited a sigmoid-shape with respect to the impeller Reynolds number indicative of three solid suspension regimes across the stirring range (1.0≤ReI≤6.25×104) investigated. The solid phase hold-up distribution was adequately captured by, εs=εs,max[1−exp(−τsppReI)]γ with εs,max and γ dependent on solid loading. An analogous expression was also obtained for the radial solid phase hold-up distribution and has enabled the proposition of a criterion for existence of radial transport gradient in gas-induced stirred tanks (GIST). Additionally, correlations for estimating the mixing time and power number for gas-induced mechanical agitators also gave good agreement with the empirical data.

► Gas-inducing mechanically stirred tank has sigmoidal dispersed phase holdup profiles.
► Solid phase holdup correlation contains parameters which explicitly depend on the solid loading.
► Solid phase hold-up radial distribution led to criterion for radial transport gradient in GIST.
► New hydrodynamically dependent expressions can predict the degree of solid mixing.