Characterization on the hydrodynamics of a covering-plate Rushton impeller

A modified Rushton impeller with two circular covering-plates mounted on the upper and lower sides of the blades was designed.There are gaps between the plates and the blades.The turbulent hydrodynamics was analyzed by the computational fluid dynamics(CFD) method.Firstly,the reliability of the numerical model and simulation method was verified by comparing with the experimental results from literature.Subsequently,the power consumption,flow pattern,mean velocity and mixing time of the covering-plate Rushton impeller(RT-C) were studied and compared with the standard Rushton impeller(RT) operated under the same conditions.Results show that the power consumption can be decreased about 18%.Compared with the almost unchanged flow field in the lower stirred tank,the mean velocity was increased at the upper half of the stirred tank.And in the impeller region,the mean axial and radial velocities were increased,the mean tangential velocity was decreased.In addition,the average mixing time of RT-C was shortened about 4.14% than the counterpart of RT.The conclusions obtained here indicated that RT-C has a more effective mixing performance and it can be used as an alternative of RT in the process industries.

Machinability of Hastelloy C-276 Using Hot-pressed Sintered Ti(C_7N_3)-based Cermet Cutting Tools

C-276 nickel-based alloy is a difficult-to-cut material. In high-speed machining of Hastelloy C-276, notching is a prominent failure mode due to high mechanical properties of work piece, which results in the short tool life and low productivity. In this paper, a newly developed Ti（C7N3）-based cermet insert manufactured by a hot-pressing method is used to machine the C-276 nickel-based alloy, and its cutting performances are studied. Based on orthogonal experiment method, the influence of cutting parameters on tool life, material removal rates and surface roughness are investigated. Experimental research results indicate that the optimal cutting condition is a cutting speed of 50 m/min, depth of cut of 0.4 mm and feed rate of 0.15 mm/r if the tool life and material removal rates are considered comprehensively. In this case, the tool life is 32 min and material removal rates are 3000 mm^3/min, which is appropriate to the rough machining. If the tool life and surface roughness are considered, the better cutting condition is a cutting speed of 75 m/min, depth of cut of 0.6 mm and feed rate of 0.1 mm/r. In this case, the surface roughness is 0.59μm. Notch wear, flank wear, chipping at the tool nose, built-up edge（BUE） and micro-cracks are found when Ti（C7N3）-based cermet insert turned Hastelloy C-276. Oxidation, adhesive, abrasive and diffusion are the wear mechanisms, which can be investigated by the observations of scanning electron microscope and energy-dispersive spectroscopy. This research will help to guide studies on the evaluation of machining parameters to further advance the productivity of nickel based alloy Hastelloy C-276 machining.

双层错位涡轮桨搅拌槽内的气液混合（英文）

Towards the objective of improving the gas dispersion performance,the dislocated-blade Rushton impeller was applied to the gas-liquid mixing in a baffled stirred vessel.The flow field,gas hold-up,dissolved oxygen,power consumption before and after gassing were studied using the computational fluid dynamics(CFD) technique.Dispersion of gas in the liquid was modelled using the Eulerian-Eulerian approach along with the dispersedκ-ε turbulent model.Rotation of the impeller was simulated with the multiple reference frame method.A modified drag coefficient which includes the effect of turbulence was used to account for the momentum exchange.The predictions were compared with their counterparts of the standard Rushton impeller and were validated with the experimental results.It is concluded that the dislocated-blade Rushton impeller is superior to the standard Rushton impeller in the gas-liquid mixing operation,and the findings obtained here lay the basis of its application in process industries.

水雾收集仿生超润湿表面的皮秒激光加工研究

雾收集被认为是解决欠发达地区水资源危机的一种有前景的方法。为了模仿和优化stenocara甲虫的天然水雾收集能力,通过皮秒激光直写技术在不锈钢上加工超疏水(疏水,超亲水)/亲水混合的图案。研究发现经过激光加工后,不锈钢的表面会从亲水变为超亲水。经过化学和热处理后,超亲水表面分别变为具有超低黏附性的超疏水表面和具有超高黏附性的超疏水(疏水)表面。本文系统地研究了原始表面(PS)、皮秒激光处理表面(LTS)、激光和化学处理表面(LCTS)、激光和热处理表面(LHTS)的水雾收集能力。发现与PS相比,所制备的表面可将水雾收集效率提高50%。这项工作为雾收集提供了一种快速而简单的方法,为开发用于现实世界的集水器提供了一个很好的选择。