Numerical investigation of unsteady mixing mechanism in plate film cooling

A large-scale large eddy simulation in high performance personal computer clusters is carried out to present unsteady mixing mechanism of film cooling and the development of films.Simulation cases include a single-hole plate with the inclined angle of 30° and blowing ratio of 0.5,and a single-row plate with hole-spacing of 1.5D and 2D(diameters of the hole).According to the massive simulation results,some new unsteady phenomena of gas films are found.The vortex system is changed in different position with the development of film cooling with the time marching the process of a single-row plate film cooling.Due to the mutual interference effects including mutual exclusion,a certain periodic sloshing and mutual fusion,and the structures of a variety of vortices change between parallel gas films.Macroscopic flow structures and heat transfer behaviors are obtained based on 20 million grids and Reynolds number of 28600.

Overlooked impact of precursor mixing:Implications in the electrochemical performance of battery electrode materials

Solid-state reactions are an essential part of the synthesis of various cathode materials for lithium-ion batteries(LIBs).Despite the simplicity and effectiveness for mass production,a subtle variation in synthesis conditions can often give rise to unexpectedly different physical properties,significantly affecting the electrochemical performance of electrode materials.However,this aspect has long been overlooked in the LIB community,which should focus on advancement in understanding the influence of synthesis conditions.As solid-state reactions occur only at the interface of precursor materials,maximizing the interfacial contact area between mixed precursor powders is crucial.Mechanical milling and/or mixing are common practices that have been performed in both academia and industry for this purpose.Unlike the common belief that this pre-treatment before calcination would be of great benefit for the preparation of high-performance LIB materials,we revealed in this work that this practice is not always successful for this goal.In our case study of the preparation of LiCoO_(2),we demonstrated that mechanical mixing-a routinely implemented process for homogeneous mixing of precursors-can be harmful if it is performed without assuring optimal working conditions for mixing.The underlying reasons for this surprising result are elucidated in this work,and we hope that this new insight can help avoid the potential pitfall of routine implementations performed for LIB materials.

Synthesis of Au-Cu Nano-Alloy from Monometallic Colloids by Simultaneous Pulsed Laser Targeting and Stirring

Experimental work has been focused on the formation of alloyed Au-Cu nanoparticles under simultaneous laser exposure and mechanical stirring of mixed monometallic colloids, here referred to as dual procedure. As a feed for the dual procedure, Au and Cu monometallic nanoparticle colloids have been using a laser ablation technique. To accomplish this, bulk targets were ablated with 1064 nm wavelength Nd: YAG laser in a pure acetone(99.99%) environment. Ultraviolet-visible optical absorption spectrometry, transmission electron microscopy, X-ray diffraction and X-ray fluorescence technique have been used to characterize the nanoparticles. It has been found that experimental conditions such as stirring and laser parameters strongly affect the synthesized particle properties, including the size, shape, composition and stability of the nanoparticles. Alloy nanoparticles containing 39% Au – 61% Cu have also been prepared in the same process, but in two forms of a homogeneous alloy and a core-shell structure.

Mixing and segregation assessment of bi-disperse solid particles in a double paddle mixer

A double paddle blender's flow patterns and mixing mechanisms were analyzed using discrete element method(DEM)and experiments.The mixing performance of this type of the blender containing bi-disperse particles has been rarely studied in the literature.Plackett-Burman design of experiments(DoE)methodology was used to calibrate the DEM input parameters.Subsequently,the impact of the particle number ratio,vessel fill level,and paddle rotational speed on mixing performance was investigated using the calibrated DEM model.The mixing performance was assessed using relative standard deviation and segregation intensity.Mixing performance was significantly affected by the paddle rotational speed and particle number ratio.Moreover,the Peclet number and diffusivity coefficient were used to evaluate the mixing mechanism in the blender.Results revealed that the diffusion was the predominant mixing mechanism,and the best mixing performance was observed when the diffusivity coefficients of 3 mm and 5 mm particles were almost equal.

Finite-time non-fragile filtering for nonlinear networked control systems via a mixed time/event-triggered transmission mechanism

This paper is aimed at investigating the problem of mixed time/event-triggered finite-time non-fragile filtering for nonlinear networked control systems with delay.First,a fuzzy nonlinear networked control system model is established by interval type-2(IT2)Takagi-Sugeno(T-S)fuzzy model,the designed non-fragile filter resolves the filter parameter uncertainties and uses different membership functions from the IT2 T-S fuzzy model.Second,a novel mixed time/event-triggered transmission mechanism is proposed,which decreases the waste of network resources.Next,Bernoulli random variables are used to describe the cases of random switching mixed time/event-triggered transmission mechanism.Then,the error filtering system is designed by considering a Lyapunov function and a sufficient condition of finite-time boundedness.In addition,the existence conditions for the finite-time non-fragile filter are given by the linear matrix inequalities(LMIs).Finally,two simulation results are presented to prove the effectiveness of the obtained method.

Continuous synthesis of dolutegravir sodium crystals using liquid-gas heterogeneous microreactor

In this work, a liquid-gas heterogeneous microreactor was developed for investigating continuous crystallization of dolutegravir sodium(DTG), as well as revealing reaction kinetics and mixing mechanism with 3-min data acquisition. The reaction kinetics models were established by visually recording the concentration variation of reactants over time in the microchannel via adding pH-sensitive fluorescent dye. The mixing intensification mechanism of liquid-gas flow was quantified through the fluorescent signal to indicate mixing process, demonstrating an outstanding mixing performance with a mixing time less than 0.1 s. Compared with batch crystallization, continuous synthesis of dolutegravir sodium using liquid-gas heterogenous microreactor optimizes crystal distribution size, and successfully modifies the crystal morphology in needle-like habit instead of rod-like habit. The microreactor continuous crystallization can run for 5 h without crystal blockage and achieve D90 of DTG less than 30 μm. This work provides a feasible approach for continuously synthesizing dolutegravir sodium, and can optimize the existing pharmaceutical crystallization.

An Eddy Perspective of Global Air-Sea Covariation

Mesoscale eddies are widely distributed in the global ocean.They affect the ocean flow field and material transport,and play an important role in the energy transfer between the ocean and the atmosphere.With the development of high-resolution satellite observations,many regional studies are emerging on the coupling effects between mesoscale eddies and the atmosphere.In this study,each identified global eddy(2010-2016,about 13 million eddies)is collocated and normalized with sea surface temperature(SST,2010-2014),sea surface wind(2010-2016),sea surface air temperature at 2 m(2010-2016),water vapor(2010-2014),evaporation rate(2010-2016),cloud liquid water(2010-2014),and rainfall rate(2010-2014).Four normalization methods are used:non-rotated normalization,and normalizations based on wind direction,flow direction,and eddy egg direction alignment.Furthermore,the eddy explained variations of the air-sea parameters are calculated to obtain their spatial distribution.The eddy explained variation ranges of the seven parameters are 24%-78%,12%-21%,3%-35%,8%-22%,9%-18%,0-53%,and0-58%,respectively.The influence of mesoscale eddies on the air-sea interface can be summarized as a vertical mixing mechanism.This study is novel in that it explores the overlying air-sea distribution from the perspective of global eddies.The numerical distributions of climatological air-sea parameters are determined by utilizing the multiyear composite overlying air-sea distribution over global eddies using the eddy coordinate system,and the contribution of eddies to this pattern is analyzed.This study is important for the investigation of global climate change.

Principle for obtaining high joint quality in dissimilar friction welding of Ti-6Al-4V alloy and SUS316L stainless steel

Ti-6Al-4V alloy(Ti64)and SUS316 L stainless steel rods were dissimilarly friction welded.Especially focusing on the detailed observation of interface microstructural evolution during the friction welding(FW),the relationship between the processing conditions,weld interface microstructure,and mechanical properties of the obtained joints were systematically investigated to elucidate the principle for obtaining a high joint quality in the FW of Ti64 and SUS316L.A higher friction pressure produced a lower welding temperature in the FW,hence suppressing the thick intermetallic compound layer formation.However,hard and brittle Ti64/SUS316L mechanically mixed layers generally formed especially at the weld interface periphery due to the high temperature increasing rate,high rotation linear velocity and high outward flow velocity of the Ti64.These harmful layers tended to induce the cracks/voids formation at the weld interfaces hence deteriorating the joints’mechanical properties.The rotation speed reduction and liquid CO2 cooling during the entire processing decreased the temperature increasing rate,rotation linear velocity and outward flow velocity of the Ti64 at the weld interface periphery.Therefore,they suppressed the formation of the harmful mechanically mixed layers,facilitated the homogeneous and sound interface microstructure generation,and finally produced a high-quality dissimilar joint in the FW of Ti64 and SUS316L.

Dry sliding wear performance of 7075 Al alloy under different temperatures and load conditions

Dry sliding wear tests were performed for 7075Al alloy under a load of 25–250 N at 25–200℃. The wear behaviors and mechanisms under various testing conditions were explored. A mild-to-severe wear transition is noticed to occur with an increase in the load at 25–200℃. With the temperature increasing, the wear loss decreases constantly under the low load of less than 50 N. It can be suggested that the 7075 Al alloy presents a high wear resistance under a high ambient temperature and low load. Its high wear resistance is found to be attributed to the existence of mechanically mixing layer (MML). The predominant wear mechanism is adhesive and abrasive wear at room temperature. With the ambient temperature and load increasing, oxidative wear and plastic extrusive wear successively prevail due to thermal oxidation and softening of matrix.