气体流量和喷嘴直径对鼓泡塔内气泡大小和形状分布的影响

通过高速摄影结合图像处理算法,研究气体流量和喷嘴直径对气泡尺寸和纵横比分布的影响。结果表明,在所有喷嘴直径下,气泡当量直径的概率密度呈现双峰分布,其中第一个峰值接近直径为1.5~2 mm的小气泡区域,另一个峰值位于较大的气泡区域。将气体流量从0.1 L/min增加到0.2 L/min会导致大气泡的概率密度更高,表明气泡聚并现象普遍存在。当气体流量增加至1.2L/min时,峰值对应的气泡直径变小,并且气泡破裂占主导地位。对于直径为1~2 mm的气泡,形状受气体流量的影响较小,而3~9 mm的气泡在所有气体流量下气泡纵横比概率密度分布的峰值均位于纵横比E=0.5处。Iguchi和Chihara提出的模型能更好地预测气泡脱离直径随气体流量的增大的变化。

卧式搅拌釜气液流动数值模拟及多目标参数优化

采用双欧拉模型、SST k-ω湍流模型和多重参考系法对搅拌釜内气液两相流动行为进行数值模拟。结果表明:在所有影响因素中,转速对搅拌釜性能的影响最大,其次是挡板宽度。通过正交试验和矩阵分析,发现最优工况为桨叶离底高度950 mm、桨叶间距1300 mm、挡板宽度525 mm和转速123 r/min。在优化工况下,保证气含率和相对功耗基本不变时,混匀时间从31.620 s缩短至25.845 s。

Three-dimensional dynamics of a single bubble rising near a vertical wall:Paths and wakes

In order to clarify the migration mechanism and wake behavior of a single bubble rising near a vertical wall,three-dimensional direct numerical simulations are implemented based on the open-source soft-ware Basilisk and various types of migration paths like linear,zigzag and spiral are investigated.The volume of fluid(VOF)method is used to capture the bubble interface at a small scale,while the gas-liquid interface and high-velocity-gradient regions in the flow field are encrypted with the adaptive mesh refinement technology.The results show that the vertical wall has an obstructive effect on the diffusion of the vortex boundary layer on the surface of the bubble migrating in a straight line,and the resulting reaction force tends to push the bubbles away from the wall surface.For the zigzag or spiral movement of a bubble in the x-y plane,the perpendicular wall is an unstable factor,but on the contrary,the motion in the z-y plane is stabilized.

Parametric study of gas−liquid two-phase flow field in horizontal stirred tank

Based on Fluent software,the gas−liquid two-phase flow in the horizontal stirred tank was simulated with SST k−ωturbulence model,Eulerian−Eulerian two-fluid model,and multi-reference flame method.The mixing process in the tank was calculated by tracer method.The results show that increasing the rotating speed or gas flow is conducive to a more uniform distribution of the gas phase and accelerates the mixing of the liquid phase.When the rotating speed exceeds 93 r/min,the relative power demand remains basically constant.The change in the inclination angle of the upper impeller has minimal effect on the gas phase distribution.When the inclination angle is 50°,the relative power demand reaches the maximum.An appropriate increase in the impeller distance from the bottom improves the gas holdup and gas phase distribution but increases the liquid phase mixing time.

Cold model on bubble growth and detachment in bottom blowing process

The bubble growth and detachment behavior in the bottom blowing process were investigated. Four multi-hole nozzle configurations with different opening ratios were assessed experimentally using high-speed photography and digital image processing. For these configurations, the experiments reveal that the bubble growth consists of a petal-like stage, an expansion stage and a detachment stage. The petal-like shape is qualitatively described through the captured images, while the non-spherical bubbles are analyzed by the aspect ratio. The bubble size at the detachment is quantified by the maximum caliper distance and the bubble equivalent diameter. Considering the dependence on the opening ratio, different prediction models for the ratio of maximum caliper distance to hydraulic diameter of the nozzle outlet and the dimensionless bubble diameter are established. The comparative analysis results show that the proposed prediction model can accurately predict the bubble detachment size under the condition of multi-hole nozzles.

Simulation on release of heavy metals Cd and Pb in sediments

The re-release process and the release rate of heavy metals,cadmium and plumbum,which are rich in sediments of a certain water area,were investigated using a combined experimental and numerical method.Results show that the release law of Cd and Pb in sediments is divided into two stages:rapid release and dynamic equilibrium,which is in great agreement with the pseudo second-order kinetic equation with a correlation coefficient R2 above 0.99.As the flow velocity accelerates,the release rate of heavy metals increases.The analysis results indicate that the water quality in the area can exceed the surface water Class V standard less than 3 h,and all but one of the relative deviations between the simulation value and the field survey result are within±10%.

Evaluation of flow behavior in copper electro-refining cell with different inlet arrangements

The arrangement of electrolyte inlet in the copper electro-refining(ER)cell has a great influence on the local flow field,which affects the distribution of electrical current density in consequence.In order to understand the complicated phenomena ofelectrolyte flow behavior in vertical counter electrodes in full-scale copper ER cell,the three-dimensional computational fluiddynamics(CFD)models with four different arrangements of electrolyte inlets,i.e.,single inlet(SI),central bottom inlets(CBI),topside interlaced inlets(TII),and bottom side interlaced inlets(BII),were established to simulate the flow behavior.Simulation resultshave revealed that the parallel injection devices help to improve the electrolyte velocity between electrodes,and while the relativerange of electrolyte velocity in CBI exceeds that of TII and BII,which is more than4times,indicating its severer unequal flowdistribution.Meanwhile,the average velocity of electrolyte in BII is4times larger than that of SI due to its higher turbulenceintensity.Generally,one of the efficient ways to supply fresh copper solution rapidly and uniformly into the inter-electrode space is toadapt the arrangement of BII.By utilizing such an arrangement,the electro-refining under high electrical current density is possible,and the productivity can be increased in sequence.

Immunogenicity of allogeneic mesenchymal stem cells Iransplanted via different routes in diabetic rats

Due to their hypoimmunogenicity and unique immunosuppressive properties, mesenchymal stem cells （MSCs） are considered one of the most promising adult stem cell types for cell therapy. Although many studies have shown that MSCs exert therapeutic effects on several acute and subacute conditions, their long-term effects are not confirmed in chronic diseases. Immunogenicity is a major limitation for cell replacement therapy, and it is not well understood in vivo. We evaluated the immunogenicity of allogeneic MSCs in vivoby transplanting MSCs into normal and diabetic rats viathe tail vein or pancreas and found that MSCs exhibited low immunogenicity in normal recipients and even exerted some immunosuppressive effects in diabetic rats during the initial phase. However, during the later stage in the pancreas group, MSCs expressed insulin and MHC II, eliciting a strong immune response in the pancreas. Simultaneously, the peripheral blood mononuclear cells in the recipients in the pancreas group were activated, and alloantibodies developed in vivo. Conversely, in the tail vein group, MSCs remained immunoprivileged and displayed immunosuppressive effects in vivo. These data indicate that different transplanting mutes and microenvironments can lead to divergent immunogenicity of MSCs.

Effects of single lance configuration on coal combustion process in tuyere from viewpoint of coal plume

Pulverized coal utilization in the blast furnace is decided by the particle flow and combustion behaviors in the raceway.Under a specific operating condition,these behaviors are directly related to the lance configuration in the upstream tuyere zone.Focusing on single straight lance,six types of single lance configurations were designed by assembling four parameters in different ways.These four parameters are the lance diameter,lance insertion angle,and the horizontal and vertical distances from the lance tip to the tuyere tip.With different lance configuration schemes applied,the pulverized coal combustion process in the lance-blowpipe-tuyere zone was simulated.The simulation results regarding particle diffusion and combustion behaviors were characterized by three indicators from the viewpoint of a coal plume.They are the plume diffusion angle,diffusion uniformity,and the average plume temperature at the tuyere outlet.To promote coal utilization,the values of these indicators under different configurations were analyzed,yielding two optimal configurations.The first one is to reduce the lance length immersed in the blowpipe-tuyere by 100 mm.The other is to increase the horizontal distance from the lance tip to the tuyere outlet by 50 mm,and the insertion angle to 11° with the lance tip located at the tuyere centerline.The findings can enhance the understanding of the influence mechanism of lance con-figuration on the coal utilization and provide guidelines for the design of new lance configurations.