Effects of impeller design, baffle, and gas flow rate on distributions of floating solid particles were examined in a stirred tank of 0.2 m i.d. for solid concentrations up to 50 vol %. Dual small cross-section impeller systems, i.e., dual four-flat blade disk turbines and dual four-pitched blade downflow disk turbines, and large cross-section impellers, i.e., Maxblend impeller and Fullzone impeller, were used. The minimum impeller speeds for off-surface floating-particle suspension decreased with aeration because bubbles rising near the tank wall enhanced the breakup of the floating-particle stagnant layer formed on the liquid surface and then the dispersion of floating particles into the liquid. The minimum impeller speeds for ultimately homogeneous floating-particle suspension also decreased with aeration. These results are contrary to those for the settling particles. The local solid particle concentrations at different heights in the stirred tank were measured. The axial solid particles concentration profiles were examined using the proposed one-dimensional floating-particle dispersion model. The Peclet numbers for floating-particle dispersion in the model were reasonably correlated in terms of impeller speed, power consumption, and forces exerted on floating particles. It was found that the large cross-section impellers could disperse completely floating particles into the liquid with less agitated speed and power consumption as compared with the dual small cross-section impeller systems used in this work.

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Proton therapy facility at Cyclotron and Radioisotope Center (CYRIC) in Tohoku University includes a horizontal beam line, currently used for research studies, and also a rotational beam irradiation system which is under construction. This system will be able to change the beam irradiation angle from 0 to 180 degree around the target and the beam delivery on the target volume is done passively using scatterers and ridge filters. In this rotational beam irradiation system due to the limitation on the available space between the beam exit window to the target location, a compact compensated contoured double scattering system was proposed to create the lateral homogeneous dose profile. This work represents the evaluation of this compact double scatterer and its application to the rotational beam irradiation system. The experiments were performed using the horizontal beam line by considering to the status of the rotational beam irradiation system in the target room 5 at CYRIC. The experimental results represent the lateral dose distribution with a proper treatment region which is in a good agreement with simulated data.

The effect of floating solid particles on volumetric gasÀliquid mass transfer coefficients was investigated using a stirred tank of 0.2 m inside diameter (i.d.) with dual four-flat blade disk turbines for solid concentrations up to 50 vol %. Two kinds of floating solids, synthetic adsorbent particles (particle size of 375 μm and wet density of 793 kg m À3 ) and polypropylene particles (particle size of 480 μm and wet density of 854 kg m À3 ) were used. At very low impeller speeds the floating particles formed a stagnant layer on the liquid surface, and none of the solids were dispersed. As the impeller speed was increased, particles were partially dispersed, and the stagnant layer volume was reduced. With further increasing impeller speed, all solids were ultimately dispersed throughout the tank. The gas hold-up and volumetric gasÀliquid mass transfer coefficient in a baffled or unbaffled stirred tank with dense floating solids particles are measured. The power consumption and gas hold-up decreased with an increase in floating solids concentration. It was found that the presence of floating solid particles significantly reduced the mass transfer coefficient at a given impeller speed. The presence of floating solids increased the apparent viscosity of the slurry and hence probably resulted in increased bubble coalescence tendency enhancing the formation of larger bubbles. They might lead to a decrease in gas hold-up or specific surface area and subsequently induce a significant decrease in the volumetric gasÀliquid mass transfer coefficient. The experimental data for gas hold-up and volumetric gasÀliquid mass transfer coefficient are satisfactorily correlated to power consumption, superficial gas velocity, and solid volume fraction.