The parallel-competing iodide-iodate reaction scheme was used to study the micromixing performance in a multi-phase stirred tank of 0.3 m diameter.The impeller combination consisted of a half elliptical blade disk tur...The parallel-competing iodide-iodate reaction scheme was used to study the micromixing performance in a multi-phase stirred tank of 0.3 m diameter.The impeller combination consisted of a half elliptical blade disk turbine below two down-pimping wide-blade hydrofoils,identified as HEDT + 2WH_D.Nitrogen and glass beads of100 μm diameter and density 2500 kg-m^(-3) were used as the dispersed phases.The micromixing could be improved by sparging gas because of its additional potential energy.Also,micromixing could be improved by the solid particles with high kinetic energy near the impeller tip.In a gas-solid-liquid system,the gas-liquid film vibration with damping,due to the frequent collisions between the bubbles and particles,led to the decrease of the turbulence level in the liquid and caused eventually the deterioration of the micromixing.A Damping Film Dissipation model is formulated to shed light on the above micromixing performances.At last,the micromixing time t_m according to the incorporation model varied from 1.9 ms to 6.7 ms in our experiments.展开更多
In order to develop turbulent drag-reducing technology by using an environmentally friendly additive in a water-transporting system,the drag reducing characteristics in a non-ionic surfactant(Oleyldimethylamineoxide,O...In order to develop turbulent drag-reducing technology by using an environmentally friendly additive in a water-transporting system,the drag reducing characteristics in a non-ionic surfactant(Oleyldimethylamineoxide,ODMAO) dilute aqueous solution flowing in a circular pipe of 5 mm diameter have been experimentally investigated with an air-driven fluid resistance test device.The rheological characteristics of the solution have also been examined by a rheometer with a cone-plate flow cell.The results show that the ODMAO solutions are drag-reducing when concentration is 400 ppm or higher,that the critical Reynolds number corresponding to the maximum drag reduction rate increases with both concentration and temperature,and that the maximum drag reduction rate can reach up to 70% in the straight pipe.At low shear rates,the shear viscosity of ODMAO solutions with a relatively high drag-reduction behaves similarly to Newtonian fluids;at above a certain critical shear rate,it is firstly shear-thickening,then shear-thinning.Such shear-rate-dependent characteristics of the shear viscosity are attributed to the different transitions of micellar network structure induced by different shear rates.Relaxation of shear stress after removing an applied constant shear rate at which the solution is in the SIS(shear-induced structure) state is found to be well expressed by a 2-step Maxwell model with a tail relaxation time much shorter than that for a drag-reducing cationic surfactant,which indicates that for the ODMAO solution,a viscoelasticity as strong as a drag-reducing cationic surfactant is not needed to realize turbulent drag-reduction.展开更多
基金Supported by the National Natural Science Foundation of China(20990224,21121064,21206002)
文摘The parallel-competing iodide-iodate reaction scheme was used to study the micromixing performance in a multi-phase stirred tank of 0.3 m diameter.The impeller combination consisted of a half elliptical blade disk turbine below two down-pimping wide-blade hydrofoils,identified as HEDT + 2WH_D.Nitrogen and glass beads of100 μm diameter and density 2500 kg-m^(-3) were used as the dispersed phases.The micromixing could be improved by sparging gas because of its additional potential energy.Also,micromixing could be improved by the solid particles with high kinetic energy near the impeller tip.In a gas-solid-liquid system,the gas-liquid film vibration with damping,due to the frequent collisions between the bubbles and particles,led to the decrease of the turbulence level in the liquid and caused eventually the deterioration of the micromixing.A Damping Film Dissipation model is formulated to shed light on the above micromixing performances.At last,the micromixing time t_m according to the incorporation model varied from 1.9 ms to 6.7 ms in our experiments.
基金supported by the Center of Natural Science and Technology of Japan
文摘In order to develop turbulent drag-reducing technology by using an environmentally friendly additive in a water-transporting system,the drag reducing characteristics in a non-ionic surfactant(Oleyldimethylamineoxide,ODMAO) dilute aqueous solution flowing in a circular pipe of 5 mm diameter have been experimentally investigated with an air-driven fluid resistance test device.The rheological characteristics of the solution have also been examined by a rheometer with a cone-plate flow cell.The results show that the ODMAO solutions are drag-reducing when concentration is 400 ppm or higher,that the critical Reynolds number corresponding to the maximum drag reduction rate increases with both concentration and temperature,and that the maximum drag reduction rate can reach up to 70% in the straight pipe.At low shear rates,the shear viscosity of ODMAO solutions with a relatively high drag-reduction behaves similarly to Newtonian fluids;at above a certain critical shear rate,it is firstly shear-thickening,then shear-thinning.Such shear-rate-dependent characteristics of the shear viscosity are attributed to the different transitions of micellar network structure induced by different shear rates.Relaxation of shear stress after removing an applied constant shear rate at which the solution is in the SIS(shear-induced structure) state is found to be well expressed by a 2-step Maxwell model with a tail relaxation time much shorter than that for a drag-reducing cationic surfactant,which indicates that for the ODMAO solution,a viscoelasticity as strong as a drag-reducing cationic surfactant is not needed to realize turbulent drag-reduction.
