An experimental investigation into the complete suspension of floating solids in an agitated tank

Abstract

Experimental work is reported on the drawdown of floating solids by agitation inside a tank. The effects of baffle configuration, type of impeller, solids concentration, and impeller clearance from the tank bottom, on the minimum drawdown speed and associated power input, are discussed. The baffle configuration did not significantly influence the minimum drawdown speed but strongly determined the power required. The power number increased with the number of baffles in any configuration. The drawdown speed was highly dependent on the type of impeller: highest and lowest values were recorded for the propeller and paddle, respectively. Solids concentration and impeller clearance from the tank bottom had a small effect on the minimum drawdown speed. However, the latter strongly affected the associated power input. Two preferred stirrer/baffle arrangements determined were (1) one baffle (three-bladed propeller) and (2) four baffles (six-bladed turbine) a t an impeller clearance of two-thirds of the liquid depth from the tank base.In several chemical processing operations, mechanical agitators are used to suspend solids in liquids to enhance solid-liquid mixing for catalytic and mass-transfer purposes. Suspension of solids heavier than the liquid medium has received extensive attention, and several correlations for calculating the required speed of agitation for complete suspension have been developed and published (Aeschbach and Bourne, 1972;Baldi et al.

Effect of vortex formation on powder sinkability for reconstituting milk powders in water to high solids content in a stirred-tank

“…There is much work presented in the literature on dispersion and solubilisation of powder in stirred-tanks however there is not much work presented on the sinking step. Thring and Edwards (1990) and Bakker and Frijink (1989) reported studies on the drawdown and complete suspension of floating solids in agitated tanks, however the experimentation was conducted with particulate solids with sizes in the range of 1-4 mm and at low suspension solids concentrations. They showed that factors, such as impeller type and baffle configuration, affected solids drawdown and the minimum speed required to obtain complete suspension.…”

Gas-Liquid Floating Particle Mixing in an Agitated Vessel

“…Ellis et al [6] paid attention to the influence of speed on the power consumption required to draw down floating particles. Thring et al [7] examined the influence of baffle configuration, impeller type and clearance on the minimum drawdown speed. Siddiqui [8] found the key to incorporate floating particles into a liquid was by controlling the vortex formation using partial baffles.…”

Influence of Floating Suspended Solids on the Homogenization of the Liquid Phase in a Mixing Vessel

“…In designing equipment for this kind of suspension, it is necessary to satisfy many of the requirements, such as the degree of mixing, the reaction rate, and an acceptable power input. Often, not all these operations are compatible, and some degree of optimization is necessary [4]. Proper choice of reactor system geometry may considerably facilitate and improve the process of solids suspension.…”