Mesoscale fabrication of a complex surface for integral impeller blades

Integral impeller is the most important compo- nent of a mini-engine. However, the machining of a mesoscale impeller with a complex integral surface is difficult because of its compact size and high accuracy requirement. A mesoscale component is usually manufac- tured by milling. However, a conventional milling tool cannot meet the machining requirements because of its size and stiffness. For the fabrication of a complex integral impeller, a micro-ball-end mill is designed in accordance with the non-instantaneous-pole envelope principle and manufactured by grinding based on the profile model of the helical groove and the mathematical model of the cutting edge curve. Subsequently, fractal theory is applied to characterize the surface quality of the integral impeller. The fractal theory-based characterization shows that the completed mesoscale integral impeller exhibits a favorable performance in terms of mechanical properties and morphological accuracy.

Study on the solid-liquid suspension behavior in a tank stirred by the long-short blades impeller

We investigated the solid–liquid suspension characteristics in the tank with a liquid height/tank diameter ratio of 1.5 stirred by a novel long-short blades(LSB) impeller by the Euler granular flow model coupled with the standard k–ε turbulence model. After validation of the local solid holdup by experiments,numerical predictions have been successfully used to explain the influences of impeller rotating speed,particle density, particle size, liquid viscosity and initial solid loading on the solid suspension behavior,i.e. smaller particles with lower density are more likely to be suspended evenly in the liquid with higher liquid viscosity. At a low impeller rotating speed(N), increase in N leads to an obvious improvement in the solid distribution homogeneity. Moreover, the proposed LSB impeller has obvious advantages in the uniform distribution of the solid particles compared with single Rushton turbine(RT), dual RT impellers or CBY hydrofoil impeller under the same power consumption.

Effect of pitched short blades on the flow characteristics in a stirred tank with long-short blades impeller

This work focuses on the design improvement of the long-short blades(LSB)impeller by using pitched short blades(SBs)to regulate the flow field in the stirred vessel.After mesh size evaluation and velocity field validation by the particle image velocimetry,large eddy simulation method coupled with sliding mesh approach was used to study the effect of the pitched SBs on the flow characteristics.We changed the inclined angles of the SBs from 30°to 60°and compared the flow characteristics when the impeller was operated in the down-pumping and up-pumping modes.In the case of down-pumping mode,the power number is relatively smaller and vortexes below the SBs are suppressed,leading to turbulence intensification in the bottom of the vessel.Whereas in the case of up-pumping mode,the axial flow rate in the center increased significantly with bigger power number,resulting in more efficient mass exchange between the axial and radial flows in the whole vessel.The LSB with 45°inclined angle of the SBs in the up-pumping mode has the most uniform distributions of flow field and turbulent kinetic energy compared with other impeller configurations.

CFD simulation of impeller shape effect on quality of mixing in two-phase gas–liquid agitated vessel

Mixing efficiency in two-phase gas–liquid agitated vessel is one of the important challenges in the industrial processes.Computational fluid dynamics technique(CFD)was used to investigate the effect of four different pitched blade impellers,including 15°,30°,45°and 60°,on the mixing quality of gas–liquid agitated vessel.The multiphase flow behavior was modeled by Eulerian–Eulerian multiphase approach,and RNG k-εwas used to model the turbulence.The CFD results showed that a strong global vortex plays the main role on the mixing quality of the gas phase in the vessel.Based on the standard deviation criterion,it was observed that the axial distribution of the gas phase in the 30°impeller is about 55%better than the others.In addition,the results showed that the 30°impeller has a uniform radial distribution over the other impellers and the maximum gas phase holdup in the vessel.Investigation of the power consumption of the impellers showed that the 30°impeller has the highest power consumption among the other pitched blade impellers.Also,examine the effect of same power condition for pitched blade impellers showed that the 30°impeller has the best mixing quality in this condition.