Thermal Analysis Simulation of Germanium Zone Refining Process Assuming a Constant Radio-Frequency Heating Source

Three-dimensional thermal a nalysis simulation of a horizontal zone refining system is conducted for germanimn semiconductor materials. The considered geometry includes a g＇ral）hite boat filled with germanium placed in a cylindrical quartz tube. A flow of Ar and H2 gas mixture is purged througll the tube. A narrow section of the, boat is assmned to be exposed to a constant heat rate produced b v an rf coil located outside the quartz tube. The results of this analysis provide essential information about various parameters such as the shape of tile molten zone, required power and temperature gradient in the system.

First-principles investigation of the effects of strain on elastic thermal, and optical properties of CuGaTe2

Based on the density functional theory, the influences of strain on structural, elastic, thermal and optical properties of CuGaTe2 are discussed in detail. It is found that the tensile strain on CuGaTe2 is beneficial to the decrease of lattice thermal conductivity by reducing the mean sound velocity and Debye temperature. Moreover, all strained and unstrained CuGaTe2 exhibit rather similar optical characters. But the tensile strain improves the ability to absorb sunlight in the visible range.These research findings can give hints for designing thermoelectric and photovoltaic devices.

The patterns of high-degree thermal free convection and its features in a spherical shell

A high-degree (degree l = 6 and order m = 0, 1, 2, [midline ellipsis] , l. High-order model for short) and steady thermal free convective motion of an infinite Prandtl number and Boussinesq fluid in a spherical shell is calculated by a Galerkin method. Convection is driven by an imposed temperature drop across top rigid and bottom stress-free isothermal boundaries only heated from below of the shell. In this paper, the scalar poloidal and fluctuating temperature fields are expanded into associated Legendre polynomials with degree l = 6 and order m = 0, 1, 2, [midline ellipsis] , l. Compared with zero-order model (degree l = 6 and order m = 0), from which 2-D longitudinal (r-θ) profiles can be obtained, high-order model can provide a series of southerly (r-θ), easterly (r-φ) and radial (θ-φ) velocity profiles, which probably reveal more detail features of mass motion in the mantle. It is found that Rayleigh number has great effects on the patterns and velocities of thermal free convection and controls the relative ratio of hot and cold plume in the shell. Probably, the present results mainly reveal the mass motion in the lower mantle, while the striking differences of convection patterns from velocities at different positions have important geodynamical significances.

Dynamic thermal modeling and parameter identification for a monolithic laser diode module

We improved the thermal equivalent-circuit model of the laser diode module（LDM） to evaluate its thermal dynamic properties and calculate the junction temperature of the laser diode with a high accuracy.The thermal parameters and the transient junction temperature of the LDM are modeled and obtained according to the temperature of the thermistor integrated in the module.Our improved thermal model is verified indirectly by monitoring the emission wavelength of the laser diode against gas absorption lines,and several thermal parameters are obtained with the temperature uncertainty of 0.01 K in the thermal dynamic process.

Calculation of thermal physical parameters of dissociated air by the dissociation degree method

The high temperature gas occurs behind shock or near the wall surface of vehicle in the hypersonic flight. As the temperature exceeds 2 000 K, 4 000 K, respectively, O2 and N2 molecules are successively dissociated. Because of variable components at dif- ferent temperatures and pressures, the dissociated air is no longer a perfect gas, In this paper, a new method is developed to calculate accurate thermal physical parameters with the dissociation degree providing the thermochemical equilibrium procedure. Based on the dissociation degree, it is concluded that few numbers of equations and the solutions are easily obtained. In addition, a set of formulas relating the parameter to the dissociation degree are set up four-species, O2 molecule The thermodynamic properties of dissociated air containing and N2 molecule, O atom and N atom, are studied with the new method, and the results are consistent with those with the traditional equilibrium constant method. It is shown that this method is reliable for solving thermal physical parameters easily and directly.

Determination of Catalytic Rate Constants towards Polymeric Conversion to Synthetic Oils: Bridging the Gap between Kinetics and Thermodynamics

Coal fly ash is being utilized as a recycling material for catalysis due to its aluminosilicate content. Catalytic conversion of polymeric wastes into synthetic gasoline and diesel through pyrolysis requires application of kinetic and thermodynamic principles. This study aimed to identify the catalytic rate constant necessary for rate law involved in reaction mechanisms and activation energy reduction needed for heat transfer rate. Stoichiometric application for balanced total series of elementary reactions is solved for the concentration determination of reactants and products. Unsteady-state in three dimensional directions of thermodynamics is derived for the determination of heat transfer rate, temperatures at any position in a sphere using Gurney and Lurie chart and center temperature in a sphere by Heisler chart. Application principles of rate law and Arrhenius equation can result to thermal conductivity as a function of activation energy leading to synthetic fuel production.

Study of Thermally Induced Vibration of Non-Homogeneous Trapezoidal Plate with Parabolically Thickness Variation in Both Directions

The present analysis demonstrates the thermal effect on vibrations of a symmetric, non-homoge- neous trapezoidal plate with parabolically varying thickness in both directions. The variation in Young’s modulus and mass density is the main cause for the occurrence of non-homogeneity in plate’s material. In this consideration, density varies linearly in one direction. The governing differential equations have been derived by Rayleigh-Ritz method in order to attain fundamental frequencies. With C-S-C-S boundary condition, a two term deflection function has been considered. The effect of structural parameters such as taper constants, thermal gradient, aspect ratio and non-homogeneity constant has been investigated for first two modes of vibration. The obtained numerical results have been presented in tabular and graphical form.

Study of Temperature Behaviour on Thermally Induced Vibration of Non-Homogeneous Trapezoidal Plate with Bi-Linearly Varying Thickness

The main aim of the present work is to study the linear temperature behaviour of a non-homogeneous trapezoidal plate whose thickness varies linearly in both directions. The temperature behaviour considered linear along the length of the plate. Non-homogeneity in plate arises due to variation in density along the length of the plate. The two-term deflection function with clamped-simply supported-clamped-simply supported boundary condition is taken into consideration. The effect of structural parameters such as taper constants, thermal gradient, non-homogeneity constant and aspect ratio has been studied. Rayleigh-Ritz method is used to solve the governing differential equations and to obtain the fundamental frequencies for the first two modes of vibration. Results are presented in graphical form.

基于恒热流法和恒温法的岩土热物性试验分析研究

目前岩土热物性测试仪采用的方法包括两种:恒热流法和恒温法,通过介绍两种测试方法的区别及模型算法,以北京市某公建项目岩土热物性测试结果为基准,利用TRNSYS软件分别模拟了恒热流法和恒温法的测试工况,针对模拟结果展开分析研究。经对比,试验时间至48 h时,两种测试方法利用软件模拟出的延米换热量与现场测试结果的误差在10%以内,表明若已知项目周边的地层热物性参数如地层的导热系数、热扩散率等,可将软件模拟结果作为前期地埋管系统设计的依据,并作为后续热物性勘察结果验证的参考数据。此外,根据模拟结果,由于夏季地埋管流体在设计工况下与土壤的温差值较大,为了使流体尽快达到设计工况点,恒温法测试时应选用较大的功率,否则48 h内的测试值结果与实际值偏差较大。

Effect of trace calcium on melting behavior of Ag-Cu-Zn brazing alloy by thermal analysis kinetics

The purity of the brazing alloys applied is necessary to be improved with the increasing cleanness of steel. Calcium is easily brought into the widely ased brazing alloy, Ag-Cu-Zn, during the producing process. This paper aims at revealing the effect of calcium on the melting behavior of the brazing alloy. The thermal analysis kinetics of silver alloy with trace calcium was studied by using differential scanning calorimetry （ DSC ） , and the enthalpy peaks were analyzed by differential methods. The rate constant of phase transformation in the probable brazing temperature range goes up with increasing calcium content, according to the values of the apparent activation energy, E, and the frequeney constant, A. It is concluded that the calcium addition could improve the melting performance of Ag-Cu-Zn brazing alloy.

膨胀型防火涂层“新-老”涂层体系的热阻

在既有老化涂层上涂覆新涂层形成“新-老”复合涂层体系,复合涂层的热阻并非既有涂层热阻与补涂涂层热阻的简单叠加.基于隔热性能试验的温度测量结果,计算复合涂层体系的等效热阻常数,通过对不同试件等效热阻常数的对比分析,考察补涂涂层对既有涂层和复合涂层热阻的影响规律.结果表明:既有涂层热阻随补涂涂层厚度增加而降低,当补涂涂层厚度大于1.0 mm时,既有涂层热阻的贡献率不超过20%,计算复合涂层热阻时可忽略不计;当补涂涂层厚度较薄(0.5 mm)且既有涂层老化时间较短(≤21循环),或既有涂层有面漆时,建议考虑既有涂层热阻的贡献(贡献率>20%).当补涂涂层与既有涂层类型不同时,复合涂层体系的热阻更大,隔热性能更好.

辉绿岩沥青混合料微波热诱导愈合性能研究

开展了辉绿岩沥青混合料微波热诱导愈合技术的应用研究。从矿料的化学组成、电磁参数上分析辉绿岩沥青混合料微波热诱导性能成因;制备了GAC-13、SMA-13、OGFC-133种级配辉绿岩沥青混合料,并采用热常数仪、微波炉对混合料的微波热诱导升温速率展开研究;通过半圆弯曲(SCB)试验研究混合料的自愈合特性。结果表明:辉绿岩沥青混合料具有一定的微波热诱导性能,辉绿岩沥青混合料应用在密级配GAC-13上的热导率和热扩散率分别为1.610 W/(m·K)、0.8483 mm^(2)/s,在断级配SMA-13中则为1.649 W/(m·K)、0.8785 mm^(2)/s,二者的抗裂性能愈合率最高可达78.3%、79.4%,在微波热诱导和传热性能上表现更优越,有利于自行愈合。

基于热网络分区等效策略的Si/SiC混合器件耦合热参数辨识方法

由硅(Si)绝缘栅双极型晶体管(IGBT)与碳化硅(SiC)金属氧化物半导体场效应晶体管(MOSFET)并联构成的混合器件可打破单一Si基器件和SiC基器件的局限性,实现损耗和成本间的有效均衡。结温估计对于Si/SiC混合器件的可靠运行至关重要,然而,目前针对热监测的研究往往需满足热稳态平衡和功率损耗可测两大条件,在实际变流器中实用性较低。基于此,该文以零输入响应法为切入点,首先,对Si/SiC混合器件热结构特性进行分析,详细阐述零输入响应法直接应用于混合器件时所带来的高阶热约束条件难以表征的问题;其次,通过对SiIGBT与SiC MOSFET进行热网络分区处理实现模型的降阶,构建出壳温降温曲线时间常数与热参数之间的约束关系,提出了基于热网络分区等效思想的混合器件耦合热参数辨识方法,所提方法简化了功率损耗测量步骤与热平衡态条件,在并联器件耦合热参数辨识研究中具有简单、通用、流程化高的应用优势;最后,通过实验验证了该文所提方法的准确性和有效性。

碳热还原氮化法制备UN粉末机理研究

氮化铀(Uranium nitride)燃料具有金属铀密度高、热导率高、热膨胀系数低及与液态金属相容性好等优点,是未来先进反应堆设计选用燃料之一。高相纯度、高活性UN粉末是制备高密度UN芯块的前提。采用碳热还原氮化法制备UN粉末,研究了工艺参数对UN粉末反应动力学、相结构、晶格常数及氮铀比的作用机制和影响规律。结果表明:UN粉末相结构与原料C/UO_(2)物质的量比及合成温度有关,当原料C/UO_(2)物质的量比为2.7、合成气氛为N_(2)-5%H_(2)(0.1~0.15 MPa)、合成温度为1700℃时,可制备得到高相纯度UN粉末;中间反应产物U_(2)N_(3)在1200℃以下、真空环境、大于2 h可分解为UN粉末;UN晶格常数与粉末中相成分有关,当N/U比接近1时,其晶格常数为0.48882 nm;合成的UN粉末经转速600 r/min、球磨时间4 h、球料比5∶1的工艺参数球磨,可制备得到粒度为0.96μm的UN细粉末。

高温热处理对环氧聚合物介电松弛的影响

为了揭示热处理对环氧树脂介电松弛的影响,本文制备了环氧树脂试样,对其进行210℃/48 h的热处理,并研究热处理前后环氧树脂化学结构、玻璃化转变温度、热分解参数、体积电阻率与介电松弛的变化。结果表明:热处理并未改变环氧树脂的化学结构与热分解温度,但使其玻璃化转变温度由134℃下降至108℃。同时,热处理后试样的介电常数变大,其中高频(106 Hz)介电常数增幅较小,而低频(10^(-1) Hz)介电常数增幅明显。

基于恒定功率的热式流量计设计与测试

针对热式流量计的温度漂移问题,提出了一种恒定功率模式下的热式流量计结构,并对其数字校准方法进行了研究。与传统热式流量计相比,增加了环境探头,该探头内嵌于流体管道壁。各传感器之间采用隔热措施,利用环境探头和感温探头测量得到的电压信号进行实时数字校准。采用音速喷嘴法燃气表检验装置对流量计进行检测。检测结果显示:流量在0.016~0.25 m^(3)/h范围内误差率小于0.5%,流量在0.25~6 m^(3)/h范围内误差率小于1.0%,温度漂移现象有效改善。

板翅式换热器传递函数动态模型及参数确定方法

飞机综合环控/热管理系统迫切需要建立快捷高效的换热器动态仿真模型,以满足先进控制系统设计需求。基于此,针对板翅式换热器动态模型,提出一种包含2个延迟环节和4个一阶惯性环节的传递函数矩阵形式,并从换热器机理模型出发,利用拉普拉斯变换推导模型中4个时间常数的计算公式,提出基于换热器效率的传热热阻计算关系式的辨识方法,解决了主要模型参数设置难题。以板翅式换热器为研究对象,在Simulink仿真平台搭建其传递函数动态模型,并与AMESim仿真平台搭建的机理模型进行对比分析,结果显示:2种模型所得空气和冷却水出口温度分别随入口温度和质量流量阶跃变化的动态响应曲线吻合很好,其中,4种工况空气和冷却水出口温度最大稳态偏差分别为0.034℃和0.029℃,当冷却水入口质量流量阶跃变化时,空气出口温度动态响应相对偏差最大,为9.27%,当空气入口质量流量阶跃变化时,冷却水出口温度动态响应相对偏差最大,为7.03%。

BF-PT-BZT三元系高温压电陶瓷的介电压电温度稳定性

采用传统固相反应法制备0.54BiFeO_(3)-0.33PbTiO_(3)-0.13Ba(Zr_(x)Ti_(1-x))O_(3)(BF-0.33PT-0.13Ba(Zr_(x)Ti_(1-x)),0.4≤x≤0.8)三元系压电陶瓷,研究了Zr含量(x)对陶瓷的微观结构以及介电、铁电和压电性能的影响。X线衍射(XRD)结果表明,BF-0.33PT-0.13Ba(Zr_(x)Ti_(1-x))三元系陶瓷为单一钙钛矿结构,当0.4≤x≤0.7时,陶瓷相结构为三方-四方相共存;当x=0.8时,陶瓷为三方相结构。扫描电子显微镜(SEM)结果表明,随着Zr含量的增加,陶瓷晶粒尺寸逐渐增加。在25~400℃时,陶瓷的压电常数d 33的波动小于±6%。当x=0.7时,BF-0.33PT-0.13Ba(Zr_(x)Ti_(1-x))具有最优异的综合性能,其介电常数εr、居里温度T_(C)、压电常数d_(33)分别为1194(1 kHz)、438℃和330 pC/N,在25~300℃时,陶瓷的电容温度系数和压电常数变化率分别为16%和8%。结果表明,BF-0.33PT-0.13Ba(Zr_(0.7)Ti_(0.3))陶瓷在高温压电器件中具有较广的应用前景。

负性光敏聚酰亚胺的种类及研究进展

由于优异的综合性能,负性光敏聚酰亚胺已成为微电子领域不可或缺的材料,根据负性光敏聚酰亚胺结构和合成工艺的不同,总结了其主要种类和研究进展。随着微电子技术的高度集成化和扇出型晶圆级封装技术的发展,对负性光敏聚酰亚胺材料提出了更高的要求,如更低的介电常数、更低的热膨胀系数和更低的固化温度等。本文进一步介绍了负性光敏聚酰亚胺材料的不同改性方法及其微观作用机制,并对比分析了各类改性方法的优缺点,为高性能负性光敏聚酰亚胺材料的设计开发提供理论基础。

不同年龄段老年人格里菲斯常数的研究

为探究夏季室内热环境中不同年龄段老年人热敏感性的差异性,拓宽传统格里菲斯常数对不同年龄段老年人的适用性,选取保定市某养老院44名60岁及以上老年人为受试者进行了现场测试,获取了3 666组主观及客观指标数据。首先,将老年人划分为3个年龄段(60~74岁、75~88岁、≥89岁),根据不同年龄段老年人的热感觉投票和平均皮肤温度的相关性计算了老年人的热中性皮肤温度;其次,分析了不同年龄段老年人在不同环境温度下的热感觉投票分布特征,得出了不同年龄段老年人的热中性温度;最后,在传统格里菲斯常数(0.5℃^(-1))的基础上作了改进和补充,提出了分年龄段主观格里菲斯常数和客观格里菲斯常数。结果表明:3个年龄段老年人的热中性皮肤温度分别为35.4、35.7、36.2℃,皮肤温度舒适区间分别为34.8~35.9、34.9~36.4、35.1~37.4℃;3个年龄段老年人的热中性温度分别为27.8、27.9、28.5℃,温度舒适区间分别为24.5~31.1、24.1~31.8、24.3~32.7℃;3个年龄段老年人主观格里菲斯常数逐渐减小,分别为0.60、0.43、0.35℃^(-1),客观格里菲斯常数也逐渐减小,分别为0.54、0.38、0.14。本文可为老年人热舒适研究和环境差异控制提供理论依据。