Browsing by Author "Šulc, Radek"
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- ItemEffect of Particle Image Velocimetry Setting Parameters on Local Velocity Measurements in an Agitated Vessel(WILEY-V C H VERLAG GMBH, POSTFACH 101161, 69451 WEINHEIM, GERMANY, 2019) Šulc, Radek; Ditl, Pavel; Jašíková, Darina; Kotek, Michal; Kopecký, Václav; Kysela, BohušAlthough they are obtained under the same conditions, results on the flow field in an agitated vessel achieved using particle image velocimetry (PIV) may vary due to differences in the PIV conditions. The influence on turbulence characteristics of the main PIV setting parameters, i.e., PIV spatial resolution, sampling frequency, and recording time, was investigated. Tests were performed with three different liquids in a developed turbulent field for a Rushton turbine impeller using two-dimensional time-resolved PIV. To obtain the relevant velocity gradients, a minimum recording time is needed. No effect of sampling frequency was observed if the sampling frequency was higher than approximately 17 times the impeller frequency, which is about three times the impeller blade frequency.
- ItemLocal velocity scaling in upward flow to tooth impeller in a fully turbulent region(E D P SCIENCES, 17 AVE DU HOGGAR PARC D ACTIVITES COUTABOEUF BP 112, F-91944 CEDEX A, FRANCE, 2019) Šulc, Radek; Ditl, Pavel; Fořt, Ivan; Jašíková, Darina; Kotek, Michal; Kopecký, Václav; Kysela, BohušThe hydrodynamics and flow field were measured in an agitated vessel using 2-D Time Resolved Particle Image Velocimetry (2-D TR PIV). The experiments were carried out in a fully baffled cylindrical flat bottom vessel 400 mm in inner diameter agitated by a tooth impeller 133 mm in diameter. Distilled water was used as the agitated liquid. The velocity fields were investigated in the upward flow to the impeller for three impeller rotation speeds- 300 rpm, 500 rpm and 700 rpm, corresponding to a Reynolds number in the range 94 000 < Re < 221 000. This means that fully-developed turbulent flow was reached. This Re range secures the fully-developed turbulent flow in an agitated liquid. In accordance with the theory of mixing, the dimensionless mean and fluctuation velocities in the measured directions were found to be constant and independent of the impeller Reynolds number. On the basis of the test results the spatial distributions of dimensionless velocities were calculated. The axial turbulence intensity was found to be in the majority in the range from 0.4 to 0.7, which corresponds to the middle level of turbulence intensity.
- ItemThe Minimum Recording Time for PIV Measurements in a Vessel Agitated by a High-Shear Tooth Impeller(MAIK NAUKA/INTERPERIODICA/SPRINGER, 233 SPRING ST, NEW YORK, NY 10013-1578 USA, 2020-03) Šulc, Radek; Ditl, Pavel; Jašíková, Darina; Kotek, Michal; Kopecký, Václav; Kysela, BohušThe flow field in a mechanically agitated vessel has often been investigated by Particle Image Velocimetry (PIV). In published studies, the recording time ranges between tenths of seconds and units of seconds. The question arises: What is the minimum recording time that is needed to obtain relevant data? Our study was aimed at determining the minimum recording time that is required to get consistent velocity field results, using the PIV technique, in a vessel agitated by a high-shear tooth impeller within the impeller flow discharge zone. Our results help to adjust PIV experimental conditions that guarantee correct velocity data. The tests were performed in a fully-baffled cylindrical flat-bottom vessel 400 mm in inner diameter agitated by a tooth impeller 133 mm in diameter, with three different liquids, using 2-D Time-Resolved PIV in the impeller Reynolds number range from 68 000 to 221 000. A statistical analysis of the radial and axial components of the mean and fluctuation velocities measured in the impeller discharge flow showed that the dimensionless minimum recording time is independent of the impeller Reynolds number. The value is N.t(Rmin) = 62 for the mean radial velocity and fluctuation velocities in both the radial direction and the axial direction, while a longer measuring time, N.t(Rmin) = 174, is required to obtain the consistent mean axial velocity for +/- 2% volatility. The dimensionless criterion N.t(Rmin) = const is recommended as the scale-up rule for an estimate of the minimum recording time.