Abstract. Tracer response experiments were carried out using a packed bed of glass beads, where fluid flowed as either a single phase (water) or two phases (water and gas) under steady unsaturated conditions. The results depended on the water saturation and could be divided into two regions at the critical water saturation, that is, the saturation at which the gas phase began to be immobile. To determine the hydrodynamic dispersion coefficients, the experimental responses were compared with the numerical results of a one-dimensional advection-dispersion equation. These results demonstrated that the hydrodynamic dispersion coefficients increased with a decrease in water saturation. [1973, 1974]
Cement is an essential materials to construct the subsurface radioactive waste disposal system. However, cementitious materials alter the groundwater pH to highly alkaline condition about 13. To comprehend the effect of such a hyperalkaline condition on the repository surroundings, this study focused on the dissolution rates of amorphous silica at [NaOH]=l0-1 mol·dm-3 . The used samples were three kinds of pure commercial silica and a natural silica scale which was obtained from inside wall of the hot-water pipe of a geothermal power plant. The observed dissolution rates were interpreted with using the model, which assumed that the particle sizes decrease with the progress of dissolution. Moreover, due to the particle size distribution anticipated in the natural silica scale, this analysis assumed it contained particles with various initial diameters. In the results, (1) all pure silica samples and at least 60 wt% of the silica scale showed good agreement of the activation energy of the dissolution in the range of 77 through 88 kJ-mol-1 in the highly alkaline solution, (2) these rate constants were of the order of 10-s_ 10-7 mol·m-2 -s-1 at around 310 K and were definitely larger than those already reported for quartz, (3) the specific surface area based on BET method was revealed to be an important factor to give the main difference in the dissolution rates between the synthetic silica and the natural silica.
Liquid Telocity distribution was measured in a bubble column 5.5 m in diameter and approximately 7 m in liquid height. Liquid flow was upward in the column center and downward near the wall. The upward velocities were from 52 to 115 cm/sec in the superficial gas velocity range from 2.4 to 8.5 cm/sec. The liquid velocity distribution is analyzed by a circulating flow model. Values of the turbulent viscosity-the parameter of the model-are in the range from 3000 to 4000 g/cm à"sec. These values agree well with those estimated by an empirical formula for turbulent viscosity proposed by Miyauchi and Shyu for smaller-diameter bubble columns.
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