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In the present study, numerical simulations of turbulent flow with free-surface vortex in unbaffled vessels agitated by a paddle impeller and a Rushton turbine, which were investigated experimentally by Nagata (John Wiley & Sons:  New York, 1974) and Ciofalo et al. (Chem. Eng. Sci. 1996, 51, 3557−3573), respectively, have been carried out. A homogeneous multiphase flow model coupled with a volume-of-fluid (VOF) method for interface capturing has been applied to determine the shapes of the gas−liquid interface and to compute the turbulent flow fields in unbaffled vessels. Turbulence is modeled using the k−ε/k−ω based shear-stress transport model (Menter, F. R. AIAA J. 1994, 32, 1598−1605) and a second-moment differential Reynolds-stress transport model. Calculations are carried out using the ANSYS CFX-5.7 CFD code (ANSYS:  Canonsburg, PA, 2004). Validation of the predictions is effected against the measured free-surface profiles (Nagata, 1974; Ciofalo et al., 1996), and the mean velocity distributions (Nagata, 1974). The predicted liquid surface profiles using the VOF method in conjunction with both turbulence models are generally in good agreement with measurements. As for the mean velocity components, the Reynolds-stress transport model predictions are superior than those obtained using the shear-stress transport model.

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Laser Doppler velocimetry measurements and computational fluid dynamic (CFD) simulations of turbulent flows with free-surface vortex in an unbaffled dish-bottom stirred tank reactor agitated by a Rushton turbine are presented. Measurements of the three mean and fluctuating components of the velocity vector are made in order to characterise the flow field and to provide data for CFD model validation. An Eulerian-Eulerian multiphase flow model coupled with a volume-of-fluid method for capturing the gas-liquid interface is applied to determine the vortex shape and to compute the flow field. Turbulence is modelled using the standard k−ε, shear-stress transport and the differential Reynolds-stress model with two variants of the pressure-strain correlation. The predicted mean flow field obtained using all four turbulence models are on the whole similar and generally in good agreement with measurements. However, the Reynolds-stress models provide somewhat better predictions of the mean axial velocity. The turbulent kinetic energy is well predicted in the flow below the impeller, near the bottom of the tank; whereas it is underpredicted in the region close to the impeller and near the wall by all turbulence models.

The reactions with natural earth materials of fission products and plutonium are of current interest in the field of atomic energy waste disposal and soil chemistry. Solutions containing less than 1 × 10‐9 moles per liter of selected radioisotopes were equilibrated with samples of a calcareous subsoil. The uptake of these radioactive isotopes by the soil was measured as a function of pH. The uptake of Cs137 was not affected appreciably by varying the pH between 4 and 10. The maximum uptake of Sr90 occurred at about pH 10 and decreased rapidly as the pH was lowered. The radioisotopes Pu239, Ce144, Zr95, ‐Nb95, Y91, and Ru106 exhibited a maximum uptake between approximately pH 4 and pH 8. Above pH 8 a region of reduced uptake occurred and persisted up to at least pH 11 for most of the polyvalent radioisotopes. The addition of high concentrations of sodium salts to the solution inhibited the uptake of both Cs137 and Sr90 by soil. A relatively small concentration of phosphate (0.01 M) added to the system was found, in effect, to nullify the interference of sodium ion with the uptake of Sr90, but the phosphate ions had no apparent influence on the uptake of Cs137.

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