Experimental and model-based investigation of the droplet size distribution during the mixing process in a batch-settling cell

Abstract

The design of a liquid–liquid gravity settler relies on the experimental investigation and model-based description of the phase separation process in a batch-settling cell. However, according to the current state of the art, the modelling assumes a monodisperse droplet size distribution (DSD), which can lead to an inaccurate settler design. This study considers the polydispersity of the initial DSD resulting from the mixing process in the settling cell to enhance the model accuracy. DSDs of o/w and w/o dispersions during the mixing process in a settling cell are investigated in this work for 2-methyltetrahydrofuran/water and decane/water material systems at hold-ups of 25–50 vol.% and stirrer speeds of 400–850 min⁻¹. Sauter mean diameters (SMD) and DSD shapes are analyzed to identify the influence of the investigated parameters on the SMD and DSD and to model the SMD and DSD. The experimental investigation shows that stirrer speed, hold-up, and interfacial tension significantly affect the DSD, while the viscosity of the continuous phase plays a minor role. The SMD is correlated to the Weber number, viscosity group, and hold-up by a model with a mean absolute percentage error (MAPE) of 3.6%. The DSD is described by a log-normal distribution function with a MAPE of 5%. The SMD and DSD models presented in this work can be used to describe the initial DSD of the phase separation process in a batch-settling cell, considering polydispersity and thus increasing the modelling accuracy of the phase separation process.