Abstract
Geometrical properties of particle deposit on the medium surface are studied in bench-scale channels (horizontal flow). A basic mathematical model describing particle deposition is presented on the spherical coordinates, which can give the ratio of the attached surface area (RA) and the angle of repose (ør) with the data of the ratio of the projected area (AA/A0).
The statistical analysis of measurements along the length and depth of the channel shows that RA(50%) of 22mm spherical media is approximately constant at 15-16% of the cumulative probability regardless of the sampling location or their sediment mass in the filter bed. This result means that suspended particles tend to be deposited within 45-48 degree of ør on the spherical medium surface. RA(50%) of 91mm Rock media is about 26.1% and 1.6-1.7 times as high as that of 22mm media. In the model calculations, the dimensionless thickness of deposits (RQ/TQ) is estimated to be 9-17% for 40-50% of the sediment porosity, and the actual volume is estimated to he about 60% of the theoretically maximum (circular cone) value since the upper media themselves block a part of the void space for the lower media where particles would be deposited. A model for prediction of the deposit mass is introduced with the following assumptions: (1) the averaged deposit volume of the rock medium equals that of the equivalent spherical medium and (2) RQ/TQ is constant regardless of the medium diameter. This model gives a good approximation with the experimental results. The model also predicts the decrease in porosity of the bed as filtration proceeds, and estimates 4% of the pore volume in the reactor at the most. Therefore, in the rock bed channel it would be expected that the deposit mass on media surface is not a main body of removed particles, but the particles would settle down to the lower layer, finally forming sediments in the bottom.
