Vertical distributions of void fraction in gas-liquid and gas-liquid-solid stirred tanks have been measured in a fully baffled dished base vessel of 0.48 m diameter, using a conductivity probe. The impeller configurat...Vertical distributions of void fraction in gas-liquid and gas-liquid-solid stirred tanks have been measured in a fully baffled dished base vessel of 0.48 m diameter, using a conductivity probe. The impeller configuration （a hollow half elliptical blade dispersing turbine below two up-pumping wide blade hydrofoils, identified as HEDT＋2WHu） recommended in previous work has been used in this work. The operating temperatures were 24℃ and 81℃, identified as cold and hot respectively. The effects of superficial gas velocity, agitator speed and the corresponding power input on the local void fraction in two-phase systems are .investigated and discussed. Results show thatth-e increasing of agitator speed or gas flow rate leads to an increase in local-void fraction at the majority of measurement points in both cold and hot systems. However, the unifo,rmity of gas dispersion does not always in crease as the raising of agitator speed and power input. In either cold or hot sparged conditions, the two- and three-phase systems.have similar vertical profiles for void fraction, with maxima in similar locations; however, the void fractions are significantly lower in hot sparging than with cold. In cold operation the presence of particles leads to a lower void fraction at most points, although the local void fractions increase a little with the addition of solid particles at high temperature, in good agreement with the global gas holdup results, and the possible reasons are discussed in this paper. This work can give a better understanding of the differences between cold-gassed and hot-sparged three phase＇stirred tanks.展开更多
The flooding characteristics of hydrofoil impeller were systematically investigated in a two-and three-phase 383 mm i.d. stirred tank operated on air, water and spherical glass beads. The volumetric solid concen-trati...The flooding characteristics of hydrofoil impeller were systematically investigated in a two-and three-phase 383 mm i.d. stirred tank operated on air, water and spherical glass beads. The volumetric solid concen-tration Cs was varied from 0 to 25%. And the superficial gas velocity Ug was at the range of 0-0.096 m·s-1. A fast and objective method for identifying flooding point NF is developed based on the statistical analysis of the pressure fluctuation signals. It is found, the effect of solid concentration on the flooding point NF depends on the gas velocity. At the lower gas velocity (Ug = 0.010 m·s-1), the solid concentration has only a minor effect. However, it displays a very significant effect on the flooding point NF at the medium and high gas velocity. The flooding point NF linearly increases with the gas velocity Ug, at lower solid concentration (Cs = 0, 10%). When Cs = 20%, the behavior of NF versus Ug becomes more complex. The correlations of the flooding characteristics in the slurry stirred tank are proposed by considering the solid concentration effect.展开更多
基金Supported by the National Natural Science Foundation of China （20576009, 20821004） and the National Basic Research Program of China （2007CB714300）. ACKNOWLEDGEMENTS The authors sincerely acknowledge the helpful discussion with Prof John M. Smith [Fluids and Systems Research Centre, School of Engineering （J2）, University of Surrey, Guildford, GU2 7XH, UK].
文摘Vertical distributions of void fraction in gas-liquid and gas-liquid-solid stirred tanks have been measured in a fully baffled dished base vessel of 0.48 m diameter, using a conductivity probe. The impeller configuration （a hollow half elliptical blade dispersing turbine below two up-pumping wide blade hydrofoils, identified as HEDT＋2WHu） recommended in previous work has been used in this work. The operating temperatures were 24℃ and 81℃, identified as cold and hot respectively. The effects of superficial gas velocity, agitator speed and the corresponding power input on the local void fraction in two-phase systems are .investigated and discussed. Results show thatth-e increasing of agitator speed or gas flow rate leads to an increase in local-void fraction at the majority of measurement points in both cold and hot systems. However, the unifo,rmity of gas dispersion does not always in crease as the raising of agitator speed and power input. In either cold or hot sparged conditions, the two- and three-phase systems.have similar vertical profiles for void fraction, with maxima in similar locations; however, the void fractions are significantly lower in hot sparging than with cold. In cold operation the presence of particles leads to a lower void fraction at most points, although the local void fractions increase a little with the addition of solid particles at high temperature, in good agreement with the global gas holdup results, and the possible reasons are discussed in this paper. This work can give a better understanding of the differences between cold-gassed and hot-sparged three phase＇stirred tanks.
文摘The flooding characteristics of hydrofoil impeller were systematically investigated in a two-and three-phase 383 mm i.d. stirred tank operated on air, water and spherical glass beads. The volumetric solid concen-tration Cs was varied from 0 to 25%. And the superficial gas velocity Ug was at the range of 0-0.096 m·s-1. A fast and objective method for identifying flooding point NF is developed based on the statistical analysis of the pressure fluctuation signals. It is found, the effect of solid concentration on the flooding point NF depends on the gas velocity. At the lower gas velocity (Ug = 0.010 m·s-1), the solid concentration has only a minor effect. However, it displays a very significant effect on the flooding point NF at the medium and high gas velocity. The flooding point NF linearly increases with the gas velocity Ug, at lower solid concentration (Cs = 0, 10%). When Cs = 20%, the behavior of NF versus Ug becomes more complex. The correlations of the flooding characteristics in the slurry stirred tank are proposed by considering the solid concentration effect.
