Investigation of mixing miscible liquids with high viscosity contrasts in turbulently stirred vessels using electrical resistance tomography

The time required to attain a sufficient degree of homogeneity i.e., mixing time, is an important parameter in mixing processes. This paper presents results from a study employing an experimental approach to estimate mixing times for a miscible Newtonian liquid mixture system with high viscosity contrasts in a turbulent stirred vessel. An Electrical Resistance Tomography (ERT) based technique has been adopted to monitor dimensionless mixing time across a range of additive viscosities, impeller designs, sizes, and speed. Dimensional analysis has been used to interpret these mixing time results in terms of the magnitude of the bulk inertia forces relative to the initial viscous forces within the added fluid. Critical non-dimensional numbers, uniting the properties of the two liquids, have been proposed as the criterion for avoiding undesirable operating conditions under which the mixing time is much longer than that required for mixing fluids with similar properties. The work proposes novel correlations for mixing time and incorporates a new dimensionless group, thereby enabling a more nuanced and accurate characterisation of mixing behaviours. This research stands to contribute to energy saving and waste minimisation efforts in the industry. It provides insights for process designers and simulation engineers, propelling a leap forward in the design and operation of mixing processes when dealing with liquid systems that have significant viscosity differences.