共查询到20条相似文献,搜索用时 205 毫秒
1.
基于流体流动模型和液相烧结作用力模型,对液相烧结第一阶段中(液相生成与固相颗粒重排阶段)液相Cu对固相W颗粒的润湿情况及颗粒的重排和密实化行为进行模拟。本模型包含Navier-Stokes(N-S)方程、区分气-液两相流的VOF方程及颗粒所受作用力(毛细力和黏性力)方程。使用二维非定常分离隐式PISO算法求解N-S方程,描述流体流动行为;求解VOF方程以区分气-液两相流;根据颗粒所受作用力编制颗粒运动自定义程序,控制颗粒运动,描述固相颗粒在毛细力牵引及黏性力共同作用下的运动。分析烧结过程液相对固相颗粒的润湿行为及液相烧结第一阶段密实化规律。探讨润湿角、颗粒间距对毛细力大小的影响,并结合具体烧结模型研究烧结体系颗粒尺寸对密实化速度的影响及不同初始液固比与烧结体系最终孔隙率的关系。最终将模拟结果与理论分析结果进行对比,两者基本一致。 相似文献
2.
高炉冷却壁冷却水管内液固两相流的数值模拟 总被引:1,自引:1,他引:0
建立了高炉冷却壁三维物理模型.采用大型CFD软件FLUNT6.8中的欧拉多相流模型,对高炉冷却壁冷却水管内的液固两相流三维流动和污垢清洗特性进行了数值模拟研究.分析了流体的流速,固体颗粒的粒径、体积分数对流体的流动、清洗强度及清洗均匀的影响.结果表明:流体的湍流强度、壁面污垢清洗强度和压力降均随流速、颗粒粒径和体积分数的增加而增加;液固流态化清洗防垢除垢效果取决于流速、液固颗粒粒径和体积分数的合理组合;综合考虑节水节能及污垢清洗的均匀性,高炉冷却壁的最佳流速为2.0~2.5 m/s,固相颗粒粒径为3~4 mm,体积分数为5%~8%.研究结果为高炉冷却壁液固流态化污垢在线清洗的工业应用提供了理论基础. 相似文献
3.
根据颗粒增强金属基复合材料凝固过程中的颗粒 /界面作用微观机理 ,导出颗粒附近温度场 ,液 /固界面形状 ,颗粒受力情况及颗粒吞并 /推移临界条件数学模型。分析了热导率、颗粒尺寸和凝固速度不同对颗粒 /界面行为的影响。 相似文献
4.
突扩圆管内液固两相流冲刷腐蚀过程的数值模拟 总被引:5,自引:0,他引:5
对突扩圆管中液固两相流冲刷腐蚀过程进行了数值模 拟研究.冲刷腐蚀过程的综合模型可以分解为液固两相流动模型、冲刷模型和腐蚀模型.在欧 拉 坐标系下求解流体相的雷诺时均守恒方程组来模拟流体流场,通过拉格朗日坐标系下的随机 轨道模型获得固体颗粒相的运动,并考虑了流体相与固体颗粒相之间的双向耦合作用.数据 验证结果表明构建的综合模型基本上是正确可行的. 相似文献
5.
6.
7.
金属及合金挤压铸造的凝固特征 总被引:1,自引:0,他引:1
黄险峰 《中国铸造装备与技术》1997,(4):18-19
分析了金属及合金挤压铸造的成形过程与传热特点,探讨了挤压铸造时液态金属的流动规律,研究了挤压铸造凝固过程中液态金属的过冷与固-液界面溶质再分配规律及挤压铸造显著减轻合金显微偏析的机制。 相似文献
8.
采用热力学计算技术,研究了凝固过程中Al-Zn稀溶液合金的固/液界面形态线性稳定性及非线性稳定性,讨论了热力学计算技术和采用线性化二元参数在固/液界面线性稳定性和非线性稳定性判断上的差别,分析了固/液界面失稳后的界面形态演化过程,给出了固/液界面亚临界分叉范围.结果表明,采用耦合热力学计算技术能更好的与试验结果吻合,所获得的失稳区域大于采用线性化二元参数所得结果,尤其在线性稳定性判据条件下更为突出. 相似文献
9.
本文利用自行设计并加工的动态模拟装置,重点研究碳钢在液/固双相流动盐水中的腐蚀规律,影响因素以及阴极保护对防止这类腐蚀的可行性,实验结果表明,由于固相颗粒的加入,双相流中碳钢的腐蚀要比单相流中严重,其临界流速值,前者的要比后者的小,固相颗粒的种类,性质对磨损腐蚀的影响程度不同,只要固相颗粒对碳钢表面无明显磨削损伤作用时,阴极保护对于碳钢在双相流动盐水中的腐蚀也是一种有效的防护方法。 相似文献
10.
铝酸钠溶液分解过程的理论及技术研究进展 总被引:1,自引:0,他引:1
铝酸钠溶液分解是碱法生产氧化铝过程的关键环节。总结铝酸钠溶液分解过程的理论及技术研究进展,论述铝酸钠溶液分解过程的热力学和宏观动力学、铝酸钠溶液的结构及其演变规律、氢氧化铝颗粒行为、分解体系固-液界面作用调控以及铝酸钠溶液分解技术等。认为铝酸钠溶液分解过程中有利于氢氧化铝析出的含铝离子是Al(OH)-4,调控溶液中其他复杂含铝离子结构向该类结构转变则有利于氢氧化铝析出;增大分解末期体系中最小颗粒尺寸是提高分解深度的关键;协同调控分解过程中溶液物理化学性质、离子结构和固-液界面作用的原理和方法是强化铝酸钠溶液分解技术研究的基础。 相似文献
11.
AbstractThe surface energy model, which may govern particle pushing under or near equilibrium solidification conditions, is not valid when convection exists in the liquid. Experiments were carried out to show that under convection conditions, particle pushing occurred at much higher growth rates than that predicted by using the surface energy model. Several mechanisms are proposed for explaining the effects of fluid flow on particle pushing. 相似文献
12.
Using phase-field theory we demonstrate that osmotic stress may result in intense convection in solidifying eutectic systems. Under isothermal conditions the natural convection is of osmotic origin, and driven by the non-equilibrium composition field. Osmotic forces arise mostly in the interface layer, since large concentration gradients are localized near the triple junctions of the phases. Tuning friction forces at the solid-liquid interface controls the intensity of fluid flow. We have found that convection in the low friction regime significantly affects microstructural pattern formation. Osmotic convection-driven instability of the solid-liquid interface is observed that leads to cellular and dendritic eutectic crystal growth. The mechanism we propose is distinct from diffusive instability that is widely acknowledged as the main cause of cellular and fingerlike patterns. 相似文献
13.
Analysis and optimization of the HVOF process by combined experimental and numerical approaches 总被引:1,自引:0,他引:1
Thermal spraying with the HVOF technology is a well known approach to dense metallic, ceramic and cermets coatings with good mechanical properties. Any attempt for improving HVOF coating properties requires a fundamental understanding of the mechanisms that occur during HVOF spraying. Thermal spray processes are not only optimized by empirical testing and by correlation analysis between process parameters and coating properties but also with numerical approaches. Recent attempts to understand the momentum and heat transfer mechanisms between flame and particles, and thus improve the control of the thermokinetic deposition process by analysis of fundamental thermophysical and fluid mechanical processes, have led to computational modeling of the spraying process and verification of simulation results by in-flight particle analysis.This paper focuses on modeling (tracking) of the particle properties during HVOF spraying using alumina powder. The particle properties are sensitive to a large number of process parameters (e.g., gas temperature, gas expansion velocity, pressure, spraying distance, spray powder particle diameter, nozzle geometry, etc.). Variation of the operating parameters of the HVOF process (gas flow rates, stoichiometric oxy/fuel ratio, nozzle design, etc.) is performed during modeling and simulation. The SprayWatch® system for particle in-flight measurement is used for verification of the numerical analysis result. 相似文献
14.
运用离散相模型( DPM)结合半经验的磨损模型,模拟计算离心泵内非定常固液两相流动,探索固相颗粒运动以及对泵材料磨损的规律。计算中将液相视为连续介质,求解欧拉坐标系下的流体控制方程;把固体颗粒相视为离散介质,在拉格朗日坐标系下求解颗粒运动方程,采用迭代计算方法实现固液两相耦合。选取常用的IS型离心泵作为研究对象,清水作为连续相,石英沙粒作为离散相,粒径为0.05-0.2 mm,泵进口颗粒体积率为0.5%-3%。计算得到了离心泵内固液两相流场特性,得到了泵内固体颗粒群的运动轨迹和材料磨损率分布等有价值的结果。 相似文献
15.
Daojie Zhang 《International Journal of Cast Metals Research》2013,26(4):236-242
The metal matrix nanocomposites in this study consist of a A356 alloy matrix reinforced with 1.0 wt.% SiC nanoparticles that are dispersed within the molten alloy matrix using ultrasonic cavitation and induction melting technologies. The required ultrasonic parameters to achieve the required cavitation for adequate degassing and refining of the aluminium alloy as well as the fluid flow characteristics for uniform dispersion of the nanoparticles into the 356 matrix are being investigated in this study using an in-house developed magneto-hydro-dynamics model. The magneto-hydro-dynamics model accounts for turbulent fluid flow, heat transfer and solidification, electromagnetic field as well as the complex interactions between the solidifying alloy and nanoparticles using ANSYS Maxwell and ANSYS Fluent dense discrete phase model and a particle engulfment and pushing model. A parametric study was performed which includes the effects of electromagnetic field from the induction coils and the magnitude of the fluid flow. 相似文献
16.
J. Madison J. E. Spowart D. J. Rowenhorst T. M. Pollock 《JOM Journal of the Minerals, Metals and Materials Society》2008,60(7):26-30
Directional solidification of nickel-based single crystals requires control of the heat transfer, fluid flow, and phase transformations
at the solid-liquid interface during withdrawal in the Bridgman process. While the morphological details of the dendritic
structure at the solid-liquid interface influence defect formation processes, there is an incomplete understanding of this
structure as a function of alloy composition and processing conditions. A three-dimensional serial sectioning and image reconstruction
approach for characterization of the solidification front has been developed and structural characteristics of the dendritic
structure are quantified. 相似文献
17.
The fluid and particle flow field characteristics of a high-velocity oxygen-fuel (HVOF) thermal spray (TS) system are analyzed
using a two-phase flow model and simulated using computational fluid dynamics (CFD) techniques. The model consists of a conservation
equation and constitutive relations for both gas and particle phases. Compressible, turbulent flow is modeled by ak-ɛ turbulent model. A Lagrangian formulation is used to model particle trajectory, and heat and momentum transfer. The fluid
velocity fluctuations resulting from gas turbulence are simulated by a stochastic model and the particle motion in the turbulent
flow is calculated in a Lagrangian Stochastic-Deterministic (LSD) method. Details of gas flow field, particle temperature
and particle velocity histories, and particle temperature and velocity profiles in the system are presented. For the validation
of the numerical analysis, the computed results are compared with available experimental measurement. Excellent agreement
between simulations and measurements is obtained for both gas and particle flow fields. A parametric study is also conducted
for different particle sizes and different nozzle barrel lengths. The flow phenomena for different flow parameters are analyzed
and explained as the result of gas dynamics and heat and momentum transfer between the two phases. The developed methodology
provides a means to analyze, design, and optimize the TS process. The numerical analysis presents a first comprehensive, fundamental
quantitative analysis for the HVOF TS system. 相似文献
18.
目的 研究压裂泵作业过程中泵阀阀隙流场的冲蚀磨损特性,探究其主要影响因素与影响规律。方法 基于固液两相流基本理论与冲蚀模型,采用计算流体力学(CFD)方法模拟泵阀阀隙流场的冲蚀磨损行为,探究支撑剂粒径、质量流量、泵阀半锥角、阀座孔入口半径、阀盘升程等参数对泵阀冲蚀特性的影响。结果 泵阀的冲蚀磨损主要表现为支撑剂对阀盘边缘处的直接冲击与对阀座锥面处的切削作用。支撑剂粒径由0.062 5 mm增大到0.375 mm时,最大冲蚀速率增大了4.80倍,继续增大到1.5 mm时,最大冲蚀速率减小了76.12%;当其质量流量由5 g/s增大到25 g/s时,最大冲蚀速率增大了3.84倍。当泵阀半锥角由30°增大到50°,阀盘升程由5 mm增大到15 mm时,最大冲蚀速率分别减小了95.55%与92.57%;随着阀座孔入口半径由30 mm增大到50 mm,最大冲蚀速率增大了10.47倍。同时,阀盘升程的增大还会显著影响冲蚀磨损区域的分布。结论 压裂泵泵阀的最大冲蚀速率随支撑剂粒径的增大先增大后减小,随阀座半锥角与阀盘升程的增大而减小,随支撑剂质量流量与阀座孔入口半径的增大而增大。其中,泵阀结构参数对泵阀冲蚀磨损的影响更为显著。 相似文献
19.
20.
A COMPREHENSIVE MODEL OF LASER CLADDING BY POWDER FEEDING 总被引:1,自引:0,他引:1
Y.L.Huang G.Y.Liang J.Y.Su 《金属学报(英文版)》2004,17(1):21-27
A novel model was presented to predict the evolutionary development of cladding layer,and a method based on Lambert-Beer theorem and Mie‘s theory was adopted to treat the interaction between powder stream and laser beam. By using the continuum model and enthalpy-porosity method, the fluid flow and heat transfer in solid-liquid phase change system were simulated. The commercial software PHOENICS, to which several modules were appended, was used to accomplish the simulation. Numerical computation was performed for Stellite 6 cladding on steel, the obtained results are coincident with those measured in experiment basically. 相似文献