EPTT 2020

12th Spring School on Transition and Turbulence

Estimation of the energy dissipation rate in a stirred tank by 2D PIV measurements

Submission Author: Lucas Freitas de Lima e Freitas , BA
Co-Authors: Lucas Freitas de Lima e Freitas, Helder Moura, Rodrigo de Lima Amaral, Paula Silva, José Roberto Nunhez, Guilherme Castilho
Presenter: Lucas Freitas de Lima e Freitas

doi://10.26678/ABCM.EPTT2020.EPT20-0042

 

Abstract

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 turbulence flow is crucial for the control and optimization of this equipment. The 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 (T) with a pitch blade turbine (PBT) impeller of diameter D ( D⁄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.

Keywords

Turbulence flow, EDR, Spatial Resolution, Stirred tank, impeller, PIV

 

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