Regularization Method to the Parameter Identification of Interfacial Heat Transfer Coefficient and Properties during Casting Solidification

The accurate material physical properties, initial and boundary conditions are indispensable to the numerical simulation in the casting process, and they are related to the simulation accuracy directly. The inverse heat conduction method can be used to identify the mentioned above parameters based on the temperature measurement data. This paper presented a new inverse method according to Tikhonov regularization theory. A regularization functional was established and the regularization parameter was deduced, the Newton-Raphson iteration method was used to solve the equations. One detailed case was solved to identify the thermal conductivity and specific heat of sand mold and interfacial heat transfer coefficient (IHTC) at the meantime. This indicates that the regularization method is very efficient in decreasing the sensitivity to the temperature measurement data, overcoming the ill-posedness of the inverse heat conduction problem (IHCP) and improving the stability and accuracy of the results. As a general inverse method, it can be used to identify not only the material physical properties but also the initial and boundary conditions' parameters.

A Numerical Method on Inverse Determination of Heat Transfer Coefficient Based on Thermographic Temperature Measurement

The heat transfer coefficient in a multidimensional heat conduction problem is obtained from the solution of the inverse heat conduction problem based on the thermographic temperature measurement. The modified one-dimensional correction method （MODCM）, along with the finite volume method, is employed for both two- and three-dimensional inverse problems. A series of numerical experiments are conducted in order to verify the effectiveness of the method. In addition, the effect of the temperature measurement error, the ending criterion of the iteration, etc. on the result of the inverse problem is investigated. It is proved that the method is a simple, stable and accurate one that can solve successfully the inverse heat conduction problem.

Regularized determination of interfacial heat transfer coefficient during ZL102 solidification process

The interfacial heat transfer coefficient(IHTC)between the casting and the mould is essential to the numerical simulation as one of boundary conditions.A new inverse method was presented according to the Tikhonov regularization theory.A regularized functional was established and the regularization parameter was deduced.The functional was solved to determine the interfacial heat transfer coefficient by using the sensitivity coefficient and Newton-Raphson iteration method.The temperature measurement experiment was done to ZL102 sand mold casting,and the appropriate mathematical model of the IHTC was established.Moreover, the regularization method was used to determinate the IHTC.The results indicate that the regularization method is very efficient in overcoming the ill-posedness of the inverse heat conduction problem(IHCP),and ensuring the accuracy and stability of the solutions.

Calculation and experimental study on heating temperature field of super-high strength aluminum alloy thick plate

Stepped heating treatment has been applied to aluminum alloy thick plate to improve the mechanical performance and corrosion resistance.Accurate temperature control of the plate is the difficulty in engineering application.The heating process,the calculation of surface heat transfer coefficient and the accurate temperature control method were studied based on measured heating temperature for the large-size thick plate.The results show that,the temperature difference between the surface and center of the thick plate is small.Based on the temperature uniformity,the surface heat transfer coefficient was calculated,and it is constant below300°C,but grows greatly over300°C.Consequently,a lumped parameter method(LPM)was developed to predict the plate temperature.A stepped solution treatment was designed by using LPM,and verified by finite element method(FEM)and experiments.Temperature curves calculated by LPM and FEM agree well with the experimental data,and the LPM is more convenient in engineering application.

多层套管式换热器的传热过程分析计算

在传统套管式换热器的基础上,为了增加换热面积、扩大流量和强化传热,提出一种新型结构的多层套管式换热器,且对其结构、原理和特点进行概述;其次对这种换热器的传热过程进行分析简化,建立物理模型,确定传热过程的关系式;结合工程实际应用,选择冷热流体、结构参数和运行工况进行液-液和气-液换热计算,确定换热器的基本结构和应用场合。最后通过正交试验的方法,对套管表面加装直肋和螺旋翅片进一步结构优化,得到最佳的翅片的厚度、高度和间距,同时比较了在最优结构参数下换热器与传统管壳式换热器的传热特性,可供工程应用提供参考。

Grain Size Distribution and Interfacial Heat Transfer Coefficient during Solidification of Magnesium Alloys Using High Pressure Die Casting Process

The objective of this study is to predict grain size and heat transfer coefficient at the metal-die interface during high pressure die casting process and solidification of the magnesium alloy AM60. Multiple runs of the commercial casting simulation package, ProCASTTM, were used to model the mold filling and solidification events employing a range of interfacial heat transfer coefficient values. The simulation results were used to estimate the centerline cooling curve at various locations through the casting. The centerline cooling curves, together with the die temperature and the thermodynamic properties of the alloy, were then used as inputs to compute the solution to the Stefan problem of a moving phase boundary, thereby providing the through-thickness cooling curves at each chosen location of the casting, Finally, the local cooling rate was used to calculate the resulting grain size via previously established relationships. The effects of die temperature, filling time and heat transfer coefficient on the grain structure in skin region and core region were quantitatively characterized. It was observed that the grain size of skin region strongly depends on above three factors whereas the grain size of core region shows dependence on the interracial heat transfer coefficient and thickness of the samples. The grain size distribution from surface to center was estimated from the relationship between grain size and the predicted cooling rate. The prediction of grain size matches well with experimental results. A comparison of the predicted and experimentally determined grain size profiles enables the determination of the apparent interracial heat transfer coefficient for different locations.

含有机玻璃中间层的双中空玻璃物理性能试验研究

为研究间隔材料为高透明低密度有机玻璃的中空玻璃是否具有优越的热工性能,制作了几种尺寸不同、间隔材料不同、材料厚度不同的双中空玻璃进行热工性能、光学性能试验研究并对比了相关参数,探究不同检测环境下光热参数结果是否相近。结果表明:现场环境下测试结果与实验室测试结果基本相符;含有机玻璃中间层的双中空玻璃有较低的紫外线透过率,有机玻璃越厚,传热系数和遮阳系数越低;在基本不增加中空玻璃重量的基础上,含有机玻璃中间层的双中空玻璃可实现低传热系数和高可见光透过率,相较于一般双中空玻璃保温隔热性能更好,更适合用在冬寒夏热地区的阳光房或建筑采光顶中。研究结果可为该种新型双中空玻璃的广泛运用提供物理性能方面的评价依据。

基于表面及迎风面改性的锯齿翅片强化传热研究

为了在提高锯齿型翅片散热器换热性能的同时尽量控制压降损失的增大,本文采用数值模拟的方法对锯齿型翅片性能进行研究,分析了不同翅片表面、迎风面结构及尺寸参数对传热Nu、流动压降损失Δp以及综合性能η的影响规律。结果表明:无论翅片表面设置何种形状凹槽和凸起对传热的影响差异较小,但圆形凹槽和凸起对压降损失的增加最少,综合性能最优。在翅片表面设置圆形凹槽和凸起的基础上继续将翅片两端迎风面改为圆形,可使传热提高的同时减小压降损失,综合性能最多提高12.2%。圆形凹槽和凸起尺寸R=0.15 mm时,传热和压降损失的平衡达到最佳,与传统锯齿型翅片相比,平均压降损失基本不变,传热和综合性能平均提高均为8.7%。

连接件材质对保温结构一体化系统热工性能的影响分析

以石墨改性模塑聚苯板为保温芯材制作点连式保温结构一体化复合剪力墙,保温层厚度100~400 mm;连接件分为碳钢、不锈钢和玻纤3种材质,碳钢和不锈钢连接件分别进行了不同程度的塑料包裹加工。测试了不同保温层厚度及不同连接件实验墙的实际平均传热系数。结果表明:对于碳钢连接件,部分塑料包裹可以明显改善其对围护结构热阻带来的不利影响,全塑料包裹相比部分塑料包裹略有改善。不锈钢连接件塑料包裹处理后,对热阻的不利影响也随部分和全部包裹处理略有改善。保温层厚度相同时,保温材料导热系数的修正系数排序为:碳钢连接件体系>不锈钢连接件体系>玻纤连接件体系。

卫星稳态热模型参数修正方法研究

为了研究卫星稳态热模型参数的修正方法,应用Thermal Desktop和Sinda/Fluint软件对一卫星热分析模型的表面涂层热光学性质和接触换热系数进行了参数修正。研究结果显示,在对上述两种参数进行同时修正时,尽管采用多种方法,但所得出的修正结果精度都不高。针对上述问题,提出了对不确定参数进行分层修正的方法,即先修正对设备温度影响较大、与设备温度相关性较高的全局关键参数,在此基础上再进一步修正局部关键参数。分析结果表明,采用分层修正时,参数修正值与真值之间最大相对误差为3.33%,设备温度计算值与真值之间的最大误差为2.60%,和常规修正的方法相比,分层修正的修正精度大大提高。

烟气余热回收装置的参数优化分析

针对我国电站锅炉排烟温度普遍偏高的情况,提出采用烟气深度冷却器以回收烟气余热,分析了其实施的可行性.通过建立热力计算分析模型,选取影响传热效果和投资成本的结构参数和运行参数作为分析对象,并以传热系数和折算成本作为设计参考,对烟气深度冷却器的设计参数进行优化.结果表明:选取合理的结构参数和运行参数可以有效地改善传热效果,降低设备投资成本和投资回收年限,保证节能改造的技术经济性.

高温表面喷雾冷却传热系数的理论分析

以池内膜态沸腾为基础 ,将喷雾颗粒的冲击作为一种扰动 ,对喷雾冷却过程进行了建模 ,分析了水流密度、高温表面温度、雾滴尺寸、雾滴冲击速度对喷雾冷却换热系数的影响。并以一种全锥喷嘴为例 ,利用该模型进行了计算、分析 ,结果证实该模型对实际应用具有一定的指导作用。

基于正交法的直通篦齿封严齿形几何参数对换热特性影响的试验研究

为研究航空发动机空气系统中封严篦齿的换热情况,针对齿宽、封严间隙、齿高、齿距、前倾角和后倾角等6个影响直通篦齿换热特性的主要几何参数,依据正交原理设计25个不同的直通篦齿试验件,试验研究其对换热特性的影响。结果表明:在试验参数范围内,上述几何参数对对流传热系数的影响趋势有明显的区别,其影响程度由主到次的顺序为:封严间隙→齿距→齿高→齿宽→前倾角→后倾角。封严间隙和齿间距影响非常显著,齿高影响显著,齿宽有一般影响,倾角影响不显著,根据试验结果推断,对流传热系数最小的齿形结构是齿宽为0.1 mm、封严间隙为0.2 mm、齿高为5 mm、齿距为6 mm、前倾角为8°、后倾角为15°。研究结果为高性能封严系统优化设计提供了技术参考。

采用正交设计优化单晶合金定向凝固数值模拟参数(英文)

采用正交设计方法研究单晶高温合金定向凝固过程数值模拟所需参数对温度场和冷却曲线的影响。结果表明:单晶高温合金凝固曲线对模拟参数十分敏感,特别敏感于铸件与铸型之间的界面换热系数。通过正交设计获得边界条件参数使模拟结果与试验结果吻合良好。确定符合DD6单晶高温合金凝固过程的数值模拟边界条件。

电子设备液冷散热的冷却液热学性能分析

从3个方面对液冷散热器中冷却液的热学性能进行分析对比,包括不同温度下的热物理参数变化、不同流态下的热传导系数和相同功耗下的冷却液温升。以65#冷却液和PAO冷却液为例,对比分析表明在-20～70℃区间内65#冷却液在热学性能上较PAO更强,但物理参数的稳定性较PAO差。在同一电子设备系统的液冷散热器中使用这两种不同冷却液介质后,通过实验测量电子设备内各芯片的平衡温度,结果表明,65#冷却液较PAO具有更好的散热效果,芯片温升约可降低10℃。

气体绝缘输电线路温升数值计算及相关因素分析

气体绝缘输电线路(GILs)的温升计算对于其可靠性设计与运行状态监测具有重要意义。为了提高GIL温升计算的精度,建立了包含外部空气在内的GIL电磁场、流体场以及温度场耦合计算的有限元模型。迭代计算了与温度相关的焦耳热损耗,并将其按照单元映射方式耦合至温度场进行温升计算。采用多组分传输理论将SF6气体与空气的物性参数进行线性组合,实现了单一模型中存在不同流体时的换热分析。利用该模型研究了运行电流与环境温度对GIL温升的影响。对比了是否考虑气体非线性热物性参数以及变化表面对流换热系数时的温升计算结果。通过实验验证了有限元计算结果的正确性,该模型与结论为GIL设计与导体运行温度监测提供了可靠的理论依据。

汽轮机转子表面换热系数计算公式修正

以某亚临界300 MW机组汽轮机转子为例，将基于CFD＆Fluent软件采用耦合数值计算的转子换热系数作为理论值，与采用西屋及前苏联经验公式的计算结果进行比较，提出了基于西屋公式的汽轮机转子表面换热系数修正公式.利用该公式对亚临界300 MW机组和超临界600 MW机组汽轮机转子表面换热系数进行修正.研究结果表明：西屋及前苏联经验公式的计算结果与理论值的相对误差较大，且前苏联公式计算结果偏差更明显；按照本文修正公式对西屋公式的计算结果进行修正后，与理论值的相对误差降至2．4％～27％；对于同一转子可采用相同的修正系数，且能保证较快的计算速度.

超重机中的气液直接传热性能

采用热空气-水体系,在转速为200～1400 r/min、水流量为40～140 L/h、热空气范围为3～15 m3/h的实验条件下,研究了热空气-水在超重机中的传热性能。实验结果表明:总传热系数随着转速的升高而增大,随着水流量的增加而增大,但增幅减小,随着热空气流量的增加而增加。对传热单元高度的计算和分析也验证了传热效果的增强。最后推导出传热系数关联式,且进行了统计检验,所得关联式与实验数据拟合较好。

直接接触式冰浆生成器参数分析及设计要点

为了提高冰浆生成器的传热性能,采用求偏导的方法对影响冰浆生成器性能的各参数进行理论分析.根据圆断面射流理论,得到换热效率与液柱高度的关系式,结果表明:当液柱高度为喷嘴直径的50倍时,换热效率≥0.9.进一步推导体积传热系数的公式,给出冰浆生成器的设计要点:冰浆生成器高度应为喷嘴直径的100倍,冰浆生成器直径应小于喷嘴直径的14倍以避免径向传热.最后对分析结果进行了实验验证,实验与理论分析结果一致:随着气体质量流量和气体比定压热容的增加以及气体进口温度的降低、制冰溶液体积的减少,体积传热系数增加.

动物体被稳态过程热物性参数测试平台的构建

借鉴国外相关方面的研究经验以及国内覆盖材料传热性能测试技术,构建了动物体表覆盖物热物性参数测试平台,阐述了测试平台的原理、系统结构及其功能。在利用平台测试有机玻璃板的传热系数在常规范围内的检验后,初步将平台应用于黄鼬东北亚种(Mustela sibirica manchurica Brass)夏季与冬季毛被传热系数的测定。测试数据显示:夏季毛被传热系数高于冬季毛被传热系数,且存在极显著差异(P<0.01)。