共查询到19条相似文献,搜索用时 125 毫秒
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雾化喷嘴是喷射成形技术的关键部件,为验证喷嘴结构对雾化性能的影响,采用计算流体动力学方法研究不同Laval喷管喉口结构、导流管锥顶角和突出长度对喷射气体流场及导流管顶端静压强(ΔP)的影响规律。结果表明在设计紧耦合Laval喷嘴中:圆角过渡式喉口形状比尖角及柱体过渡更利于获得高速气流;较小的锥顶角可以减小导流管出口静压值,但速度衰减较大;导流管突出长度在7~8 mm时可以获得较好的气动效果。最后选定圆角过渡Laval形出气口形状,导流管锥顶角β=45°以及突出长度h=8 mm加工雾化喷嘴并进行雾化实验,在雾化压强0.8 MPa时7055合金粉末以球状或类球状形态存在,质量中径为42.3μm。 相似文献
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《有色冶金设计与研究》2020,(5)
雾化喷嘴是水力雾化锌粉工艺的关键设备之一,其结构的合理性,直接决定水雾化锌粉工艺的成败。在研发以水为工作介质的高压大流量雾化喷嘴过程中对喷嘴内部的流场进行了全面的CFD分析,研究了喷嘴结构参数锥面间隙和喷射内夹角对其射流性能的影响。研究结果表明:在锥面间隙h=0.3 mm、射出内角α=60°条件下,喷嘴综合性能最优。基于本次研究的新型喷嘴设计合理,能满足水雾化锌粉工艺要求。 相似文献
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A thermokinetic model coupling finite-element heat transfer with transformation kinetics is developed to determine the effect
of deposition patterns on the phase-transformation kinetics of laser powder deposition (LPD) process of a hot-work tool steel.
The finite-element model is used to define the temperature history of the process used in an empirical-based kinetic model
to analyze the tempering effect of the heating and cooling cycles of the deposition process. An area is defined to be covered
by AISI H13 on a substrate of AISI 1018 with three different deposition patterns: one section, two section, and three section.
The two-section pattern divides the area of the one-section pattern into two sections, and the three-section pattern divides
that area into three sections. The results show that dividing the area under deposition into smaller areas can influence the
phase transformation kinetics of the process and, consequently, change the final hardness of the deposited material. The two-section
pattern shows a higher average hardness than the one-section pattern, and the three-section pattern shows a fully hardened
surface without significant tempered zones of low hardness. To verify the results, a microhardness test and scanning electron
microscope were used. 相似文献
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A study of laser energy transfer efficiency, melting efficiency, and deposition efficiency has been conducted for the laser-engineered
net-shaping process (LENS) for H-13 tool steel and copper powder deposits on H-13 tool steel substrates. This study focused
on the effects of laser deposition processing parameters (laser power, travel speed, and powder mass flow rate) on laser beam
absorption by the substrate material. Measurements revealed that laser energy transfer efficiency ranged from 30 to 50 pct.
Laser beam coupling was found to be relatively insensitive to the range of processing parameters tested. Melting efficiency
was found to increase with increasing laser input power, travel speed, and powder mass flow rate. A dimensionless parameter
model that has been used to predict melting efficiency for laser beam welding processing was investigated for the LENS process.
From these results, a semiempirical model was developed specifically for the LENS processing window. Deposition efficiency
was also investigated and results show that under optimum processing conditions, the maximum deposition efficiency was approximately
14 pct. A semiempirical relation was developed to estimate deposition efficiency as a function of process efficiencies and
LENS processing parameters. Knowledge of LENS process efficiencies measured in this study is useful to develop accurate heat
flow and solidification models for the LENS process. 相似文献
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Shape-selective catalysts for the disproportionation of toluene were prepared by the modification of the cylinder-shaped ZSM-5 zeolite extrudates with chemical liquid deposition with TEOS (tetraethyl orthosilicate).Various parameters for preparing catalysts were changed to investigate the suitable conditions. The resulting catalysts were tested in a pressured fixed bed reactor and characterized by SEM (scanning electron microscopy). The conversion of toluene and para-xylene selectivity were influenced remarkably by the n(SiO2)/n(Al2O3) ratio of ZSM-5 zeolite, the type and amount of deposition agent, acid and solvent used, and the time and cycle of deposition treatment. TEOS was proved to be a more efficient agent than the conventional polysiloxanes when the depositionamount was low. The catalyst prepared at the suitable conditions exhibited a high para-xylene selectivity of 91.1% with considerable high conversion of 25.6%. SEM analyses confirmed the formation of a layer of amorphous silica on the external surface of ZSM-5 zeolie crystals, which was responsible for the highly enhanced shape-selectivity. 相似文献
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采用有限元软件ANSYS/LS-DYNA建立了15个颗粒与基板的冷喷涂沉积模型,通过多颗粒沉积模型预测工艺条件、不同颗粒/基板组合的沉积行为和微观形貌;制备了Al和Cu冷喷涂涂层,观察了涂层截面形貌和颗粒变形特征,并与模拟结果进行对比.结果表明,多颗粒沉积模型可预测喷涂条件对颗粒沉积过程及涂层微观特征的影响,以及不同颗粒/基板组合的界面微观形貌.当碰撞速度低时,颗粒变形不充分,颗粒交界处易形成孔洞;随着速度增加,颗粒流变填充孔洞,涂层致密.与颗粒相比,硬基板涂层/基板界面平滑,机械互锁作用小;软基板形成射流状金属挤入颗粒之间,增加结合作用. 相似文献
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In this article, the electrodeposition process of Cu-Sn alloy powders from tripolyphosphate (TPP)-based electrolytes was investigated
as a function of deposition parameters. The effects of deposition parameters such as current density, electrolyte composition
(Cu/Sn mole ratio), mechanical stirring speed, and temperature on the Cu content of alloy powder and cathodic current efficiency
were evaluated using the response surface methodology (RSM). The empirical models developed in terms of deposition parameters
were found to be statistically adequate to describe the process responses. The study revealed that as far as the copper content
was concerned in the alloyed powders, all parameters selected had positive correlations. However, a high stirring speed and
low current density led to a greater current efficiency. The morphology and chemical composition of the electrodeposited Cu-Sn
alloy powders were investigated using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray
diffraction (XRD), and inductively coupled plasma (ICP) analysis. An SEM analysis showed that the powder morphology was affected
considerably by the cathodic current density and stirring speed. 相似文献
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Recently ,Bihasattractedmuchattentionforap plicationsinvolvingfieldandcurrentsensingduetoitsextremelyhighmagnetoresistance (MR )relativetothosereportedforGMRandCMRmaterials .ThelargeMRofBiarisesfromitspeculiarelectronicstructure .Ithasasmallenergyoverlap (~38meV)betweentheLconductionandTholebands ,smalleffectivemasses(atthebandedge ,me=0 0 0 2m0 ) ,andhighmobil ities .Becauseoftheseproperties ,Bihasfrequentlybeenusedforquantumconfinementstudiesinquan tumwellandquantumwiregeometries[1] … 相似文献
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喷射沉积过程是一个多参数共同影响的复杂过程。通过对雾化器往复扫描规律以及其它工艺参数的研究,可以对喷射沉积过程进行工艺优化。基于对沉积过程的分析,建立了雾化器往复扫描喷射沉积的数值模型。采用计算机数值模拟技术与实验结合的方法,着重研究了喷射成型过程中雾化器的扫描运动对成型的影响;实验证明,根据分析所得到的雾化器扫描曲线,可以准确预测这类成型产品的形状和尺寸。 相似文献
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The current work examines the heat-and-mass transfer process in the laser multilayered cladding of H13 tool steel powder by
numerical modeling and experimental validation. A multiphase transient model is developed to investigate the evolution of
the temperature field and flow velocity of the liquid phase in the molten pool. The solid region of the substrate and solidified
clad, the liquid region of the melted clad material, and the gas region of the surrounding air are included. In this model,
a level-set method is used to track the free surface motion of the molten pool with the powder material feeding and scanning
of the laser beam. An enthalpy–porosity approach is applied to deal with the solidification and melting that occurs in the
cladding process. Moreover, the laser heat input and heat losses from the forced convection and heat radiation that occurs
on the top surface of the deposited layer are incorporated into the source term of the governing equations. The effects of
the laser power, scanning speed, and powder-feed rate on the dilution and height of the multilayered clad are investigated
based on the numerical model and experimental measurements. The results show that an increase of the laser power and powder
feed rate, or a reduction of the scanning speed, can increase the clad height and directly influence the remelted depth of
each layer of deposition. The numerical results have a qualitative agreement with the experimental measurements. 相似文献
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Anu Sharma Ken Kawamoto Per Moldrup Lis Wollesen de Jonge Toshiko Komatsu 《Canadian Metallurgical Quarterly》2011,15(4):275-284
Understanding colloid mobilization, transport, and deposition in the subsurface is a prerequisite for predicting colloid-facilitated transport of strongly adsorbing contaminants and further developing remedial activities. This study investigated the transport behavior of soil-colloids extracted from a red-yellow soil from Okinawa, Japan. Different concentrations of suspended-soil colloids (with diameter <1??μm) were applied, at different flow velocities and pH conditions, to 10-cm long water-saturated columns repacked with either Narita (mean diameter D50 = 0.64??mm) or Toyoura (mean diameter D50 = 0.21??mm) sands. The transport and retention of colloids were studied by analyzing colloid effluent breakthrough curves (BTCs), particle size distribution in the effluent, and colloid deposition profiles within the column. The results showed a significant influence of flow velocity: Low flow velocity caused tailing of colloid BTCs with higher reversible entrapment and release of colloids than high flow velocity. The finer Toyoura sand retained more colloids than the coarser Narita sand at low pH conditions. The deposition profile and particle size distribution of colloids in the Toyoura sand clearly indicated a depth-dependent straining mechanism. By fitting colloid transport models (one-site and two-site models) to the colloid effluent breakthrough curves, transport and deposition of colloids in Narita sand at low pH were best described by a one-site attachment-detachment model, whereas colloid transport and deposition in Toyoura sand at low pH were better captured by a two-site attachment, detachment, and straining model. The coupled effects of solution chemistry, colloid sizes, and medium surface properties have a dominating role in particle-particle and particle-collector interactions in colloid transport and deposition. 相似文献