Electrochemical behavior of Ti-6.5Al-2Zr-1Mo-1V alloy under rotating condition with periodically fluctuating current density

Titanium alloy plays a crucial role in the electrochemical field due to its excellent corrosion resistance.The passivation and dissolution behaviors of Ti-6.5Al-2Zr-1Mo-1V(TA15)alloy in Na Cl solution were studied by simulating the electrochemical machining process in a rotating condition,which made the anode in a state with alternating high and low current density.Electron probe micro analysis,ultra-depth microscope,scanning electron microscope,and X-ray photoelectron spectrometer were used to reveal the evolution of TA15 under fluctuating current density.The existence state of the passivation film on TA15 surface was closely related to the pulse frequency of the periodically fluctuating current density.At higher pulse frequency of 0.20 Hz,the material was hardly dissolved because passivation dominated the electrolysis behavior,while at lower pulse frequency of 0.01 Hz,the passivation and dissolution behaviors occurred alternately with the variation of the current density.Herein,the thickness of the passivation film was inversely proportional to the applied current density.Due to the different electrochemical characteristics of a phase andβphase,the surface of the TA15 changed from being smooth to porous after a period.In addition,the change of microstructure affected the content of O^(2–)and exposed the suboxides of titanium.In a word,the change of pulse frequency and current density affected the electrochemical behavior of TA15,which was different from the conventional steady condition.

Numerical Simulations of Liquid-Solid Flows in A Vertical Pipe by MPS-DEM Coupling Method

In the process of deep-sea mining,the liquid-solid flows in the vertical transportation pipeline are very complex.In the present work,an in-house solver MPSDEM-SJTU based on the improved MPS and DEM is developed for the simulation of hydraulic conveying.Firstly,three examples including the multilayer cylinder collapse,the Poiseuille flow and two-phase dam-break are used to validate the precision of the DEM model,the pipe flow model and MPS-DEM coupling model,respectively.Then,the hydraulic conveying with coarse particles in a vertical pipe is simulated.The solid particle distribution is presented and investigated in detail.Finally,the coupling method is successfully applied for the simulation of the liquid-solid flows in a vertical pipe with rotating blades,which shows the stability of the solver under rotating boundary conditions.This fully Lagrangian model is expected to be a new approach for analyzing hydraulic conveying.

Hot-wire experimental investigation on turbulent Prandtl number in a rotating non-isothermal turbulent boundary layer

This experiment used a parallel array of hot wire probes to simultaneously measure the temperature and velocity fields in the non-isothermal turbulent boundary layer of a rotating straight channel. The Reynolds numbers are 15,000 and 25,000, respectively. The rotation numbers are 0, 0.07, 0.14, 0.21 and 0.28, respectively. The purpose of this study is to calculate the turbulent Prandtl number in a rotating non-isothermal turbulent boundary layer. Due to the difficulty in measuring local turbulent Prandtl numbers, this study focuses on the average turbulent Prandtl numbers in the logarithmic region instead. Under static conditions, this value is taken as 0.9 normally. This research finds that rotation conditions can affect the turbulent Prandtl number by affecting the properties of velocity and temperature boundary layers. The change range of the turbulent Prandtl number is roughly 0.6–1.1. The influence of the leading side is greater than that of the trailing side, especially at high rotation numbers. This can provide validation and guidance for numerical simulation. Other information within the turbulent boundary layer is also discussed. It is hoped that this study would enhance our understanding of the mechanism of turbulent flow in the turbulent layer at rotating conditions.

Effects of Interfaces on Dynamics in Micro-Fluidic Devices：Slip-Boundaries' Impact on Rotation Characteristics of Polar Liquid Film Motors

A new approach for exploring effects of interfaces on polar liquids is presented. Their impact on the polar liquid film motor(PLFM) – a novel micro-fluidic device – is studied. We account for the interface's impact by modeling slip boundary effects on the PLFM's electro-hydro-dynamical rotations. Our analytical results show as k = l_s/R increases(with ls denoting the slip length resulting from the interface's impact on the film's properties, k >-1 and R denoting the film's radius):(a) PLFMs subsequently exhibit rotation characteristics under "negative-", "no-", "partial-" and"perfect-" slip boundary conditions;(b) The maximum value of the linear velocity of the steady rotating film increases linearly and its location approaches the film's border;(c) The decay of the angular velocities' dependency on the distance from the center of the film slows down, resulting in a macroscopic flow near the boundary. With our calculated rotation speed distributions consistent with the existing experimental ones, research aiming at fitting computed to measured distributions promises identifying the factors affecting ls, e.g., solid-fluid potential interactions and surface roughness.The consistency also is advantageous for optimizing PLFM's applications as micro-washers, centrifuges, mixers in the lab-on-a-chip.