Using Tomography Technique to Characterize the Continuous-Flow Mixing of Non-Newtonian Fluids in Stirred Vessels

Abstract

Chemical industries often encounter non-Newtonian fluids with yield stress such as pulp suspensions, certain polymer and biopolymer solutions, and wastewater sludge. The visualization of the non-Newtonian fluid flow inside the stirred vessels is a challenging task since the vast majority of these fluids are opaque. Electrical resistance tomography (ERT) is a non-invasive flow-visualization technique which can be utilized effectively for the evaluation of the mixing of opaque fluids. In this study, a cylindrical mixing vessel equipped with a top-entering impeller was employed to mix the xanthan gum solution, which is a pseudoplastic fluid exhibiting yield stress. The main objective of this study was to employ the ERT technique in the continuous-flow mixing of non-Newtonian fluid in order to explore: (i) the effect of the impeller type (radial-flow and close clearance impellers) on the flow pattern generated inside the stirred tank (ii) the effect of inlet-outlet flow on the deformation of the cavern. The 2D and 3D tomograms enabled us to visualize the flow of the opaque fluid and to identify the existence of channeling and dead volume inside the stirred vessel in the continuous-flow mixing system. Moreover, the tomography images revealed that the cavern volume increased due to the deformation created by the inlet-outlet flow.