共查询到19条相似文献,搜索用时 109 毫秒
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基于非Fourier定律,建立了脉冲激光加热条件下单相二元合金表面快速重熔和凝固过程的非平衡传热传质模型,并根据碰撞理论和Aziz的连续生长模型处理固/液界面,以解释快速熔凝过程界面动力学的非平衡效应,快速熔凝问题是涉及热质传输的移动界面问题,通过二阶精度的Von Neumann隐式差分格式和界面跟踪方法进行过程模型的数值求解。应用该模型,分析了Al-Cu二元合金的激光表面熔凝过程,结果表明,激光的高能量密度和非平衡界面动力学所引起的熔化过程和凝固过冷对于快速熔凝过程的影响很大,在快速熔凝过程中,界面速度的变化很大,且因基底材料和热流大小而不同,通过计算获得了界面温度,速度、溶质浓度及非平衡分配系数随界面位置的变化,结果显示,在凝固过程中界面速度和界面溶质浓度都存在着很大的波动。 相似文献
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脉冲微孔喷射法(POEM)制备微米级球形粒子是典型的无容器传热和凝固过程,制备出的球形粒子具有粒径均一、圆整度高、热履历一致等特点,对流和辐射主导的传热机制对其制备工艺、凝固过程和组织控制至关重要。针对脉冲微孔喷射法微米级球形金属粒子的制备过程、冷却传热与凝固特征,本文建立了三维球坐标系下的粒子传热与凝固数值计算模型,考虑纯Cu粒子在无约束凝固过程中的对流和辐射换热特点,采用温度回升法处理纯金属的凝固潜热,计算了金属粒子在凝固过程不同阶段的温度变化与分布特点,考察了粒子凝固进程中的温度梯度、冷却速率、液固界面推进与凝固速度;模拟分析粒子的对流、辐射换热特征及贡献强度,探讨了不同制备工艺对粒子对流换热的影响,为POEM法微米级球形粒子制备工艺的优化和凝固过程调控提供参考。 相似文献
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准确设置边界条件是保证数值模拟精度的前提。本文针对凝固过程中的轴对称铸件建立相应的反传热模型求解其界面换热系数,对Pro CAST仿真的温度值与正传热算法计算结果进行了比较,证实了正传热算法的计算精度,进而对比假设的实际热流与反算的热流值,验证了建立的轴对称反传热模型计算界面换热系数和界面热流的有效性及准确性。 相似文献
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采用有限差分法建立了高温钢板连续喷水冷却过程中一维非稳态传热条件下冷却水换热系数的计算模型,将试验测量到的数据应用该模型计算出了试验过程中冷却水与高温钢板间的换热系数[h。]分析结果表明:在流量一定的情况下,压力对换热系数的影响较明显,而在压力一定的情况下,流量对换热系数的影响较小,冷却水的换热系数随喷水密度的增加而增大,随钢板表面的温降呈先增加后减小的趋势。总结出了钢板表面温度为400~1 000 ℃,喷水密度为90~180 L/(m2·min)的条件下,喷水冷却换热系数[h]的经验计算公式。 相似文献
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在一堆凝固传热条件下,通过多点非线性估计方法计算得出界面换热系数与界面处冷铁一侧温度的关系(h-T_(ic))曲线。本文认为此曲线较换热系数与时间的关系(h-τ)曲线更为本质地反映了界面热交换的特征,并首次将h-T_(ic)曲线应用于一般铸件的凝固模拟,获得了满意的计算结果。本文还考察了铸件/冷铁界面换热条件的不同处理方法对模拟蛄果的敏感性。采用计算机图形显示技术处理数据。 相似文献
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铝合金活塞铸件的温度场数值模拟研究 总被引:5,自引:4,他引:1
开发了三维温度场计算程序,模拟了活塞铸件在不同界面换热系数下的金属型凝固进程,说明界面换热系数对金属型凝固速度影响很大,可作为调节金属型凝固的控制因素。同时还对比说明了相对计算的意义。 相似文献
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文中设计了模铸实验并采用喷水冷却方式来模拟AZ31镁合金半连铸一冷区传热过程,得到了用于反求界面换热系数的温度变化曲线。采用反热传导法求解了不同冷却水量下熔体-模具间的界面换热系数,并分析了冷却水量对界面换热系数的影响。结果表明,随着冷却水量的增加,界面换热系数峰值与冷却水量呈正相关,冷却水量由20 L/min提高到60 L/min时,换热系数峰值从1 425.8 W/(m2·K)增加到2 727.5 W/(m2·K),且高冷却水量的换热系数峰值出现在低的温度;随着冷却水量的增加,从铸坯边部到中心的凝固组织均匀性明显提高。 相似文献
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铝带坯双辊铸轧过程瞬态传热数学模型 总被引:1,自引:1,他引:1
采用拉格朗日随体坐标建立了铝双辊铸轧过程瞬态传热数学模型。在数学模型中考虑了金属凝固动力学条件和采用试验测定的辊/铝带坯界面接触换热系数边界条件,用有限差分方法对控制方程进行了数值求解,并由现场测试数据验证了传热数学模型的正确性。 相似文献
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Based on the heat transfer theory and liquid solidification theory, the heat transfer during the rapid solidification process of amorphous ribbons prepared by melt spinning was approximately modeled by one-dimensional heat conduction equation. Besides, integration with the temperature gradient, the relationship between the ribbon thickness and solidification time was derived according to the boundary conditions of ribbon-copper wheel. A simply theoretical model was obtained to calculate the cooling rates of aluminum amorphous ribbons. According to the above theoretical model, the critical cooling rate of aluminum amorphous ribbons by melt spinning is above 10^6 K/s, which proves that the aluminum based alloys belong to the marginal glass forming ability of alloys. The calculated results are in good agreement with other estimated values reported previously. 相似文献
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1 INTRODUCTIONHighintensitylasersurfaceprocessinghasbecomeoneoftheimportanttechnologiesforthefabricationofnewmaterialsandtheimpr 相似文献
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Segregation of iron atoms during refining of aluminum using the fractional solidification technique has been analyzed. The
redistribution of the solute atoms was influenced by the solidification and solid/liquid interface tangential velocities.
Aluminum purity increased with decreasing solidification velocity and increasing tangential velocity. The diffusion boundary
thickness was inversely proportional to the square root of the tangential velocity in the cylindrical rotating system. Effects
of the tangential and solidification velocities on the effective redistribution coefficient were investigated. The calculated
refining curves were in good agreement with measured values. 相似文献
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赵九洲 《中国有色金属学会会刊》2002,12(3):366-369
A model has been developed for the calculation of the microstructural evolution in a rapidly directionally solidified immiscible alloy.Numerical solutions have been performed for Al-Pb immiscible alloys.The results demonstrate that at a higher solidfication velocity a constituteional supercooling region appears in front of the solid/liquid interface and the liquid-liquid decomposition takes place in this region.A higher solidification velocity leads to a higher nucleation rate and ,therefore,a higher number density of the minority phase droplets.A s a result,the average radius of droplets in the melt at the solid/liquid interface decreases with the solidification velcity. 相似文献
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Heat transfer at the metal-die interface has a great influence on the solidification process and casting structure. As thin-wall components are extensively produced by high pressure die casting process(HPDC), the B390 alloy finger-plate casting was cast against an H13 steel die on a cold-chamber HPDC machine. The interfacial heat transfer behavior at different positions of the die was carefully studied using an inverse approach based on the temperature measurements inside the die. Furthermore, the filling process and the solidification rate in different finger-plates were also given to explain the distribution of interfacial heat flux(q) and interfacial heat transfer coefficient(h). Measurement results at the side of sprue indicates that qmax and hmax could reach 9.2 MW·m~(-2) and 64.3 kW ·m~(-2)·K~(-1), respectively. The simulation of melt flow in the die reveals that the thinnest(T_1) finger plate could accelerate the melt flow from 50 m·s~(-1) to 110 m·s~(-1). Due to this high velocity, the interfacial heat flux at the end of T_1 could firstly reach a highest value 7.92 MW·m~(-2) among the ends of T_n(n=2,3,4,5). In addition, the q_(max) and h_(max) values of T_2, T_4 and T_5 finger-plates increase with the increasing thickness of the finger plate. Finally, at the rapid decreasing stage of interfacial heat transfer coefficient(h), the decreasing rate of h has an exponential relationship with the increasing rate of solid fraction(f). 相似文献
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将结晶器移出感应加热器,使连续定向凝固时固液界面控制在结晶器出口;结合传热边界条件,求解连续定向凝固熔体区、液/固界面、空冷区和水冷区的一维稳态温度场方程,得出线坯最大稳态拉坯速度随熔体温度、结晶器长度、冷却距离和冷却水流量的变化规律;并基于直径为6 mm的Cu-12%Al(质量分数)线材制备的工艺条件,对理论解进行实验验证和讨论.结果表明:Cu-12%Al线材的最大稳态拉坯速度随熔体温度升高而降低,且降低速率逐渐减小,其中在1 150~1 300 ℃范围内降低37.3%;最大稳态拉坯速度随结晶器长度增加而增加,且增加速率逐渐减小,其中在20~40 mm范围内增加28.5%;最大稳态拉坯速度随冷却距离增加而降低,且降低速率逐渐减小,其中在4~12 mm范围内降低68.8%;冷却水流量在100~400 L/h范围内最大稳态拉坯速度变化不明显.当固液界面前沿温度梯度小于2.02 ℃/mm时,实际拉坯速度无法达到理论最大稳态拉坯速度;当固液界面前沿温度梯度大于4.17 ℃/mm时,最大稳态拉坯速度实验值和理论值吻合较好. 相似文献
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对矩形冷坩埚定向凝固钛铝合金熔体流场开展数值模拟研究。结合实验结果,建立熔体流场的3-D有限元模型,研究不同电源参数下熔池内流动特性。计算结果表明:熔池内存在着复杂的循环流动,在固液界面前端存在着较为强烈的径向对流,并在中部合流。熔体流动随着电流强度的增强而增强,但是宏观流动形貌并没有改变。当电流为1000A时,熔池内最大流速为4mm/s,固—液界面前端达到3mm/s。当频率从10kHz变化到100kHz时,熔池流动形貌发生明显改变,分析其影响机制。对于冷坩埚定向凝固,存在着一个最佳频率。 相似文献