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针对单晶锗微切削热传导问题,采用移动热源法分别建立了在剪切滑移面热源和前刀面摩擦热源作用下单晶锗的微切削温升理论模型,计算了单晶锗三种切削速度下的最高切削温度,同时以同类硬脆性材料单晶硅的切削温度对此模型进行了验证。通过单点金刚石车削实验,利用红外热像仪对单晶锗微切削过程中的温度进行了在线测量。实验测量结果与模型计算结果对比发现,不同切削速度下,单晶锗的最高切削温度变化趋势一致,切削速度越大温度越高,其相对误差在2.56%~6.64%之间;单晶硅的最高切削温度相对误差为3.84%。模型能够对单晶锗及同类硬脆性材料的温度场进行较准确的预测,为研究其热效应提供进一步理论支持。 相似文献
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采用多模式微波谐振法,开展了定压气体折射率基准测温系统中谐振腔材料电解精炼韧铜(Cu-ETP)线性热膨胀系数的高精度原位实验测量及其不确定度分析研究,温度范围为4.3~299 K.针对不同的温度区间,采用了降温法(5~299 K)和控温法(4.3~26 K)两种实验测量方案,通过降温法测得的线性热膨胀系数标准不确定度优于2.2×10-7 K-1,其中,重复性是其测量不确定度的主要来源;通过控温法测得的线性热膨胀系数标准不确定度优于2.9×10-9 K-1,微波模式一致性和重复性是其测量不确定度的两大主要来源.由于控温稳定性高、微波测量噪声低,控温法所获得的线性热膨胀系数结果更为精确.最后,按照温区范围进一步发展了该系统内Cu-ETP材料线性热膨胀系数的计算方程,实现了实验数据与温度的高精度关联. 相似文献
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建立了电渣重熔轴对称瞬态耦合模型,研究了电极更换对电渣重熔过程中电磁场、流场、温度场、热平衡和电极端部熔渣凝固行为的影响。结合旋转矢量法和谐波法对电磁场求解,采用动态网格技术描述铸锭生长,建立渣池与电极间的瞬态导热模型,准确预测电极熔化速率。结果表明,原电极脱离后,0~100 s,渣池表面热损失最多增加了2.1倍,热平衡改变,渣池温度从1 933.3 K降低到1 720.3 K,熔池轮廓向内缩紧,且外侧变化更明显。在新电极加热阶段,电极端部形成一层固态渣壳,热源恢复,渣池温度从1 720.3 K增加到1 901.2 K,渣壳由外侧向内熔化。结合响应面分析法,重熔电流、电极预热温度均与固态渣熔化时间呈正相关,原电极脱离时间呈负相关,其中重熔电流影响最为明显。 相似文献
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根据电子束焊接焊缝形貌特征及其深宽比大等特点,选用复合热源作为热源模型.通过线性插值等方式估计材料热力学参数随温度变化,模拟Ti基非晶合金电子束焊接温度场.模拟结果与实际焊缝取得良好的吻合,验证了热源模型的准确性.获得一定变量参数下电子束焊接钛基非晶合金温度场及热循环曲线.在温度场的基础上再进行焊接应力场的模拟,获得残余应力分布曲线.实验验证整个焊件没有晶化相析出,验证了该焊接工艺的可行性. 相似文献
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以烧结机烟气低温余热的有机朗肯循环发电为研究对象,选用R245fa, R113以及R600a三种适合低温热源的干工质,分析了蒸发温度、冷凝温度、热源温度、热源质量流量等操作参数对低温余热循环发电系统的输出功率和?效率的影响.该研究内容同样适用于其他低温热源的有机朗肯循环发电热力学性能分析. 相似文献
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为了合成居里温度在室温附近的钙钛矿磁致冷材料,用简单的无机原料,采用水热合成法合成了La0.65Ca0.18Sr0.17MnO3钙钛矿材料.用粉末X射线衍射表征材料的相组成,用扫描电镜(SEM)观测样品形貌,用直接法测量材料的绝热温变.通过研究水热合成条件如碱度、水热温度、水热时间等对其样品磁热效应的影响,确定水热合成的最佳条件为碱度4 mol·L-1、水热温度240 ℃、水热时间80 h.该条件下合成的样品为单一钙钛矿相,由能谱图知不同形貌的晶体具有相同的成分.此材料的居里温度为323 K,最大绝热磁温变为0.29 K. 相似文献
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Ag/La2NiO4基电触头使用中温度场的有限元分析和实验研究 总被引:2,自引:2,他引:0
通过对电触头使用过程中闭合电弧→接触电阻焦耳热→分断电弧→自然冷却过程的分析, 建立了一个可描述电触头使用过程中, 瞬态温度场的统一计算模型.通过对Ag/La2NiO4基电触头的电接触实验机和相关实验的测试、分析和计算, 得到进行该电触头使用中瞬态温度场计算所需的基本参数.在此基础上, 采用有限元方法进行了计算, 得到了该电触头的瞬态温度场的分布和演化特点.通过将计算结果与相关的实验测量结果进行分析和比较, 可以发现瞬态温度场对于Ag/La2NiO4基电触头材料的侵蚀机制、使用寿命的研究具有重要参考价值. 相似文献
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一、前言在工业生产和科学研究中,经常需要准确地测量高温气流的温度。采用热电偶直接和高温气流接触使之热交换达到平衡进行温度测量,由于测量方法十分简单,得到了广泛的应用。但是这种平衡法由于热电偶材料的限制,不能测量较高的气流温度, 相似文献
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根据稳定态下多层平壁炉衬传热原理,介绍了炉衬各层间温度及热流密度的计算方法。利用VB编程环境中的可视化编程,建立各种耐火材料的热传导系数数据库,有利于平壁层数及材质种类等参数的选取,输入热面温度及各层平壁厚度,计算出炉衬相应的各种参数。在实际应用中,该程序性能稳定,界面美观。 相似文献
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摘要:高炉炉缸内衬表面形成稳定的凝铁层将延长高炉寿命。采用自制的凝铁层模拟实验装置,在中温高压条件下利用锡与焦炭制备凝铁层模拟样品;通过三维数码显微镜观察统计不同凝铁层模拟样品对应的金属与焦炭的面积比,采用瞬态平面热源法测定导热系数,探究其对凝铁层导热系数的影响。结果表明,凝铁层模拟样品(凝锡层)的导热系数范围是23.58~40.39W/(m·K);凝铁层样品的导热系数范围为28.05~48.19W/(m·K);还原凝铁层真实导热系数后,可以确定高炉炉缸区域传热模型中的气隙厚度为0.5~1.0mm。 相似文献
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C. C. Aydiner E. Ü:Ustü:UndaG J. C. Hanan 《Metallurgical and Materials Transactions A》2001,32(11):2709-2715
The viscoelastic nature of bulk metallic glasses (BMGs), their low thermal conductivity, and the fast cooling used in their
processing subject them to thermal tempering. This process leads to a residual stress state in which compression on the surface is balanced by tension in the interior.
For the first time, we have calculated such stresses in metallic glasses by adapting an analytical instant-freezing model
previously developed for silicate glasses. This model has been demonstrated to be reasonably accurate in predicting the final
residual stresses, although, due to its very nature, it neglects transient effects. For an infinite plate geometry and employing
processing parameters often used for metallic glasses, we predict that significant residual stresses can be generated in these
materials during thermal tempering. Preliminary measurements conducted using the layer-removal method yield compressive residual
stress values close to model predictions. 相似文献
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The thermal and energy performance of buildings depends on the thermal characteristics of the building envelope, and particularly on the thermal resistance of the insulation material used. The performance of the thermal insulation material is mainly determined by its thermal conductivity, which describes the ability of heat to flow across the material in the presence of a differential temperature. The value of the thermal conductivity of a particular material is subject to variation, due to changes in both moisture content and temperature. In reality, thermal insulation in buildings is exposed to significant and continuous temperature variations, due to varying outdoor air temperature and solar radiation. However, when calculating cooling loads or performing energy analyses for buildings, most designers, if not all, use published or manufacturer-supplied values of thermal conductivity, which are normally evaluated at 24°C according to the ASTM standards. Currently, many types of insulation materials are produced in Saudi Arabia, but not enough information is available to evaluate their performance under the prevailing climatic conditions. The objective of this paper is to present the results of a study that investigates the relationship between the temperature and thermal conductivity of various types of locally produced insulation materials. Additionally, the impact of thermal conductivity variation with temperature on the envelope-induced cooling load for a theoretically modeled building is quantified and discussed. Results are expected to clarify the issue of thermal conductivity dependence on temperature and lead to a more accurate assessment of the thermal and energy performance of buildings. 相似文献
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L. J. B. Smith S. F. Corbin R. L. Hexemer Jr. I. W. Donaldson Donald Paul Bishop 《Metallurgical and Materials Transactions A》2014,45(2):980-989
The objective of this research was to design aluminum powder metallurgy (PM) alloys and processing strategies that yielded sintered products with thermal properties that rivaled those of the cast and wrought aluminum alloys traditionally employed in heat sink manufacturing. Research has emphasized PM alloys within the Al-Mg-Sn system. In one sub-theme of research, the general processing response of each PM alloy was investigated through a combination of sintering trials, sintered density measurements, and microstructural assessments. In the second, the thermal properties of sintered products were studied in detail. Thermal conductivity was first determined using a calculated approach through discrete measurements of specific heat capacity, thermal diffusivity, and density and subsequently verified using a transient plane source technique on larger specimens. Experimental PM alloys achieved >99 pct theoretical density and exhibited thermal conductivity that ranged from 179 to 225 W/m K. Thermal performance was largely dominated by the amount of magnesium present within the aluminum grains and, in turn, bulk alloy chemistry. Data confirmed that the novel PM alloys were highly competitive with even the most advanced heat sink materials such as wrought 6063 and 6061. 相似文献
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以Cu基预合金粉为基体,加入SiC、Si_3N_4、B4C多元陶瓷作为颗粒增强相,利用粉末冶金法通过真空热压烧结工艺制备了SiC、Si_3N_4、B4C多元陶瓷/Cu基复合材料,并用激光脉冲法测试其室温条件下的导热性能。研究发现,随着SiC、Si_3N_4、B4C多元陶瓷含量的增加,复合材料的热导率逐渐减小,特别是当SiC、Si_3N_4、B4C多元陶瓷总质量分数大于15.0%以后,热导率急剧下降。复合材料内部的孔隙以及晶界、晶格畸变、位错等缺陷是影响热导率的主要因素。要获得导热性能良好的复合材料,应严格控制SiC、Si_3N_4、B4C多元陶瓷的质量分数在15.0%以内,并且可以考虑通过退火以及二次挤压等方法进一步提高致密度,减少烧结体内的位错、孔隙等缺陷,从而提高导热性能。 相似文献
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