Abstract
Velocity measurements of the flow field in an agitated vessel are necessary for the improvement and better understanding of the mixing processes. The obtained results are used for the calculations of the impeller pumping capacity, comparison of the power consumption etc. We performed various measurements of the local velocities in an agitated vessel final results of which should be processed for several purposes so it was necessary to make an analysis of the obtained data suitability and their quality. Analysed velocity data were obtained from the LDA (Laser Doppler Anemometry) and PIV (Particle Image Velocimetry) measurements performed on a standard equipment where the flat bottomed vessel with four baffles was agitated by the six-blade Rushton turbine. The results from both used methods were compared. The frequency analyses were examined as well as the dependency of the data rates, time series lengths etc. The demands for the data processed in the form of the ensemble-averaged results were also established.
Highlights
Measurements of the velocity profiles were carried out in a flat bottomed mixing vessel, with water as the working liquid
The results of the obtained velocity profiles of the radial velocity component from both methods PIV and LDA are depicted in figure 2 where the mean ensemble-averaged velocity is normalised by the impeller tip speed
The results of the radial mean ensemble-averaged velocity obtained from the LDA and PIV measurements are in good agreement in the region of the impeller outflow stream
Summary
Measurements of the velocity profiles were carried out in a flat bottomed mixing vessel, with water as the working liquid (density ρ = 1000 kg · m−3, dynamic viscosity μ = 1 mPa · s). The stirred vessel diameter was T = 300 mm, filled with liquid to the level H = T. The measurements were carried out with impeller speed 300 rpm, when Reynolds number was 5.0·104, which represents turbulent regime (Re > 104) for agitated vessel. In turbulent regime the mean velocity and fluctuations are dependent only on impeller tip speed Vtip and geometry. The velocity profiles are depicted in dimensionless form. The positions are in dimensionless form where z/H is ratio of the total liquid depth and represents vertical position which is parallel with the axis of the impeller shaft.
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