14. Estimation of the Energy Dissipation Rate in a Stirred Tank by 2D PIV Measurements

Stirred tanks agitated by impellers are used in a wide range of industries, e.g., chemical, food, pharmaceutical, and petroleum. The tank design, the impellers, and the number and type of baffles are often associated with their application. Thus, the experimental investigation of these parameters in the turbulent flow is crucial for the control and optimization of this equipment. Particle Image Velocimetry (PIV) is a non-intrusive and quantitative technique that allows determining the vector fields of the flow using tracers. The distribution obtained by this method can also assist in the validation of CFD simulations. The objective of this work is to estimate the energy dissipation rate (EDR) of a stirred tank from PIV 2C-2D measurements and its relation with the spatial resolution. The work was conducted in 0.38 m diameter tank (\(\mathrm{T}\)) with a pitch blade turbine (PBT) impeller of diameter D (\(\mathrm{D}/\mathrm{T}=1/3\)) in water. The angle-resolved PIV enables a number of turbulent features to be identified. Hence, measurements were taken for three angles, 0°, 45°, and 75°. The EDR was estimated using four methodologies: by the assumption of local axisymmetry (AS), by direct estimation (DE), by modified direct estimation (MDE), and by large eddy simulation (LES). For the optimization and reduction of possible errors, different processing strategies were used to decrease the noise level of the PIV measurements. This study showed that values of EDR were found to vary by two orders of magnitude from near the impeller to the circulation region of the tank. Herein, the effect of measuring angle on EDR was analyzed and provided an insight into the anisotropy of the turbulence in the stirred tank. However, EDR estimation is exceptionally challenging due to the lack of knowledge to distinguish its accuracy and the influence of spatial resolution.