Flow field and homogenization time assessment in continuously-fed stirred tanks

This paper focuses on the fluid dynamic characteristics of a laboratory scale fully baffled vessel stirred by different impellers and provided with one inlet and one outlet for the continuous feed of the working liquid.The specific aim of the investigation is the assessment of the operating conditions (namely the agitation speed and the inlet flowrate) at which the feed stream effects start to be significant from an engineering point of view.The effect of the inlet jet on average flow field (as obtained by Particle Image Velocimetry) and on homogenization time (as obtained by Planar Laser Induced Fluorescence) is quantified.The results show that the inlet stream modifies the mean flow field features more importantly the smaller the agitation speed is, as compared with the feed flow rate. The jet affects the overall fluid dynamics in terms of general flow pattern and local turbulence values. It is shown that the jet stream gives rise to a substantial reduction of mixing times (in the order of 15 to 30%, depending on the agitator adopted) with comparatively small additional power inputs (less than 5% of impeller input).