Flow of Non-Newtonian Fluids through a Vortex-Based Hydrodynamic Cavitation Device

Hydrodynamic cavitation (HC) is being increasingly used for a variety of industrially relevant processes such as biomass pretreatment, emulsions, and crystallization. Many of these processes involve non-Newtonian fluids. However, most of the previous studies on characterizing flow in cavitating devices focus on low-viscosity, Newtonian fluids. In this study, we investigate the influence of non-Newtonian, particularly shear-thinning behavior of fluids on the flow characteristics and cavitation inception in a vortex-based hydrodynamic cavitation device (VD) using both experiments and computational fluid dynamics (CFD) simulations. Primary digestate from an anaerobic digester was considered as a model non-Newtonian fluid, considering increasing applications of HC devices for biomass pretreatment. The non-Newtonian behavior was represented using the Carreau rheological model. The parameters of the model were obtained via rheological measurements over a shear rate range of 10 to 1300 s^-1 of two digestate slurries containing 50% (v/v) and 77% (v/v) with water. The case of water was used as the reference case. A three-dimensional (3D) CFD simulation of flow in VD was performed by using the Eulerian mixture model. The SST k-ω turbulence model and the Singhal cavitation model were used. Simulations were validated by comparing the simulated pressure drop across VD with the experimental measurements. Simulation results show that the 50% (v/v) and 77% (v/v) digestate slurries exhibit a reduction in swirl intensity in the vortex chamber and a delayed cavitation inception compared with the reference case of water. The results were analyzed to bring out the influence of higher effective viscosity and non-Newtonian behavior on the flow characteristics of VD. The presented results will be useful for designing VD for high-viscosity applications in waste valorization.