钢坯加热的数值模拟

借助CFD仿真手段,模拟蓄热式加热炉内钢坯加热的实际状况,研究了钢坯长度、宽度方向上下表面和中心温度的温度分布,提出钢坯存在上下温差、四角边缘温度高和靠近出钢口钢坯温度低等问题。同时,研究了炉内不同厚度钢坯与加热时间的基本关系,比较了仿真计算结果与实际炉内加热时间,通过数值拟合,得出钢坯厚度与加热时间的拟合公式,可在生产实际中使用。上述研究结果可为加热炉钢坯加热制度的制定和优化提供依据。     

LOCA条件下包壳材料感应和电阻加热温升行为的对比研究

目的使有限元模拟技术成为一种切实有效的研究方法,进而为高性能反应堆包壳材料的设计以及可能发生的LOCA(Loss of Coolant Accident)事故下的应急措施等提供理论依据。方法基于COMSOL软件模拟分析典型锆合金核材料在LOCA条件下分别经感应加热和电阻加热后的温升行为。结果感应加热条件下,锆材的体积内最高温度、体积平均温度与表面中心点温度的差值随着温度上升逐渐增大,在1200℃瞬时温度下,温度差值最高,约为41℃。电阻加热条件下,锆材的体积内最高温度、体积内中心温度与表面中心点温度在加热的整个阶段近乎重合,最大差值约为3℃;锆材的体积平均温度、表面平均温度与表面中心点温度的差值出现负值,最大差值约为30℃。结论电阻加热和感应加热虽均适用于堆外研究反应堆失水事故下包壳材料所面临的超高温度及超快升温速率的工况模拟,但限于实际工况下电阻加热速率的滞后性,推荐使用感应加热进行后续的模拟研究工作。相关结果可为高性能反应堆包壳材料的设计提供必要的理论依据。     

应用于电池热管理的均温板的温度特性研究

本文以一款内部具有流道以及相变工质R1233zd的均温板为研究对象,将均温板置于冷源与热源之间,对其温度场进行了理论分析和仿真模拟,并通过搭建实验台,对均温板的温度特性进行了实验研究。实验结果表明:均温板表面温度分布与冷源表面温度分布具有良好的一致性。均温板表面温度分布受热源功率和冷源温度的影响:当热源功率由345 W升至690 W,而冷源温度保持0℃不变时,均温板表面平均温度由13. 20℃升至25. 84℃,表面温差由11. 10℃升至25. 70℃;当冷源温度由0℃降为-5℃,而热源功率保持690 W不变时,均温板表面平均温度由25. 84℃降至18. 15℃,表面温差由25. 70℃降至16. 60℃。在不同工况下,均温板热阻约为0. 03 K/W,具有良好的导热性能。     

碳化硅合成过程的测试技术及模拟研究

利用CFD软件对碳化硅合成炉内的温度场、压力场及速度场进行模拟,并建立传热-变形-应力耦合模型对电极通电过程的温度及应力进行分析。同时实验室通过自主设计的测温装置和集气装置对合成炉内炉芯附近温度及气体流速变化进行监测。研究表明模拟结果与实验数据基本吻合,随着合成时间的延长,炉内热量呈辐射状向外扩散,8h炉芯温度可达2600℃,炉芯周围碳化硅开始分解,此时电极最高温度处约为423℃,可在电极与空气接触的表面喷涂一层隔绝空气的耐高温涂层防止电极高温氧化,炉内8h左右反应生成的气体达到峰值,对应此时炉内压力也达到最大,生产时可在出现高压之前降低供电功率,同时加入少量木屑增加炉底透气性来改善因压力过高所造成的喷炉事故。     

玻璃钢化加热过程的初步分析

为加深对玻璃钢化过程的认识,提高工艺参数调控的合理性,建立了钢化炉加热段中玻璃板加热升温过程的数学模型,并用数值方法进行了求解分析.玻璃厚度、表面辐射率、加热方式对玻璃板加热过程有重要影响.计算得到的不同厚度的玻璃板加热到既定温度所需时间与工厂生产实践的数据基本吻合.结果表明,加热Low-E玻璃宜采用对流辐射加热模式,对流传热系数应控制在50W/(m2·℃)左右.加热初期,玻璃板内的温差可达82℃(对6mm厚玻璃),采用双室式加热是合理的.     

毛细管辐射吊顶表面温度的动态变化特性

毛细管网在结构层内换热是一个三维传热过程,吊顶表面温度的动态变化特性非常复杂。采用CFD数值模拟,得到毛细管吊顶表面温度随供水温度及时间变化的动态曲线。     

基于双蒸发器压缩制冷系统的激光器散热方案设计及实验研究北大核心CSCD

设计用于高功率激光器泵浦源散热的双蒸发器压缩制冷系统,通过优化设计两相流冷板内部流道,保证换热能力的同时,得到极小的板面温差。利用第二蒸发器以及压缩机待机运作产生的制冷量减小激光器芯片在变工况启动时的温度升降,避免温度剧烈波动。实验结果表明,在4组环境温度(15℃、25℃、35℃、40℃)以及3组散热工况(2 kW、3 kW、4 kW)下,通过设置合理的压缩机转速与膨胀阀的开度,可以控制表面温度处于20—30℃之间,且监控点最大温差低于1℃,系统能效比处于2.5—9区间。在变工况运行试验中,控制制冷系统直接启动,发现监控点温度剧烈波动,温度最高可达49.75℃,同一时刻监控点间最大温差达9.72℃;利用第二蒸发器实现系统待机启动,监控点温度缓慢升高至稳定区间,升温过程中温度波动极小,表明利用本系统可以实现对高功率器件的稳定散热。     

热金属气压成型电磁感应加热有限元模拟

应用感应加热理论,利用麦克斯韦方程组和温度微分方程,建立了电磁场与温度场耦合的有限元数学模型,使用有限元分析软件ANSYS对热金属气压成型工艺中的电磁感应加热过程进行了模拟与分析。模拟结果表明:随着电磁感应线圈电流频率的提高,在相等的加热时间内,金属钢管的升温速度不断增加,且最终达到的温度也进一步升高。随着电磁感应线圈电流密度的增加,在相等的加热时间内、相同的电磁感应线圈电流频率下,金属钢管的升温速度不断增加,加热效率得到有效提高,且最终达到的温度也逐步升高。随着金属钢管与线圈的间隔增加,金属钢管内、外表面的温度均逐渐降低;外表面温度的降低趋势越来越平缓,而内表面温度的降低趋势则不断加剧。     

TC4薄壁件热处理过程形状尺寸变化数值预报

建立了钛合金薄壁件加热冷却过程中温度场和应力场的数学模型,利用ANSYS软件实现了对钛合金筒形件加热冷却过程中形状尺寸变化及残余应力的预报.结果表明:钛合金筒形件随炉升温至1 050℃,保温700 s后淬火至25℃,直径方向最大相对变形为 1.057%;上下边缘处单元应力状态为张应力,此处的残余应力为389 MPa;淬火过程中工件心部和外表面最大温差为150℃.     

复合材料固化工艺的直热模具温度场均匀性分析

针对复合材料固化成型工艺的直热模具温度场均匀性进行了研究。建立模具温度场和复合材料固化反应温度场的耦合传热学模型,并对该模型进行有限元建模仿真分析。针对影响模具表面温度均匀性的主要因素,即电加热管的间距和功率,设计正交试验优化,优化后模具表面最大温差为3.5℃,达到行业标准。此外,对影响温度场均匀性的其他因素,即加热管与模具的接触热阻、复合材料层合板厚度进行了探讨,接触热阻的存在使得模具表面最大温差达到7.24℃,模具加热到指定温度多用时800 s,降低了效率。研究层合板对模具温度均匀性的影响时发现未加入复合材料时模具表面最大温差为4.44℃,加入层合板耦合后最大温差为3.5℃;厚度为毫米级时,层合板对直热模具表面温度均匀性影响不大。      

A cylindrical furnace for absorption spectral studies

A cylindrical furnace with three heating zones, capable of providing a temperature of 1100°C, has been fabricated to enable recording of absorption spectra of high temperature species. The temperature of the furnace can be controlled to ± 1°C of the set temperature. The salient feature of this furnace is that the material being heated can be prevented from depositing on the windows of the absorption cell by maintaining a higher temperature at both the ends of the absorption cell.     

Multizone Furnace for Analysis of Fixed-Point Realizations in the Range from 1,000°C to 1,700°C

In this article, the development of a laboratory furnace specially designed for analysis of fixed-point plateau realizations in the range from 1,000 °C to 1,700 °C that enables control of various temperature distribution settings along the heating zone length is presented. A total of 13 thermocouples are built into the furnace tube wall to control the temperature as well as to measure the temperature distribution. The furnace is divided into seven independently controlled heating zones. Each heating zone comprises a MoSi₂ heating element and its dedicated DC power supply module. The furnace temperature is controlled by manipulating the output voltage of each power supply to control the temperature of each heating element, as estimated from its electrical resistance. The heating power and temperature measurement are fully controlled by a computer using an application written in Lab VIEW, allowing very flexible furnace control. The furnace can be used in air as well as in an inert atmosphere. Measurements of the temperature distribution of the furnace during a melting-point realization are presented.     

Effect of heating rate on porous TiAl-based intermetallics synthesized by thermal explosion

TiAl-based porous materials were synthesized by a novel process of thermal explosion (TE) reaction. The effects of heating rate on the expansion behavior of powder assemblies, phase compositions, and pore structures were investigated. Results showed that the actual temperature of specimen increased rapidly from 655 to 661°C (furnace temperature) to 1018–1136°C (combustion temperature) in a short time interval of 25–55?s, indicating that an obvious TE reaction occurred at different heating rates (1, 2, 5, and 10°C min^?1). TE reaction in Ti/Al powder assemblies resulted in the formation of open-celled TiAl-based intermetallics. When the heating rate was set at 5°C min^?1, the maximum open porosity of 59% was obtained in Ti-Al bodies, which experienced the highest combustion temperature (1136°C) and underwent maximum volume expansion (48%). The pore size distribution was uniform and pores were interconnected in TE products.     

Durability of cementitious binder derived from industrial wastes

The durability of cementitious binder hydrated at 27°C and 50°C under high humidity was examined by alternate wetting and drying, as well as heating and cooling, cycles at temperatures ranging from 27°C to 60°C and by performance in water. The results show that cementitious binder hardened at 50°C possesses higher water resistance and lower porosity than the binder hardened at 27°C. A decrease in the strength of the cementitious binder was observed with an increase in temperature and in the wetting and drying and heating and cooling cycles. The maximum decrease in strength occurred at 60°C. The cementitious binder cured at 27°C showed a much smaller decrease in strength with a rise in temperature and in weathering cycles. The changes in strength of the cementitious binder were monitored by differential thermal analysis and microscopy.     

相变材料用于可拆卸护臂热防护服的实验研究

针对传统降温服降温效果差、续航时间低、能耗高、噪声大等问题,本文通过应用相变恒温材料Na2SO4·10H2O在高温时发生相变吸收热量的特性,设计了一种应用于夏季高温环境的人体作业可拆卸护臂的热防护服,并在此基础上进行了热水模拟热源实验和真人实验。结果表明：在热水模拟实验中,防护服在30、41、45 ℃的工况下,前胸、侧腹、后背、腹部4测点温度在60 min升至最高,4测点平均温度最终能降至约26 ℃,其中在30 ℃工况下防护服降温性能较好,在45 ℃工况下降温性能较差。在真人实验中,防护服在37.1、39、41 ℃工况下,3 h内4测点平均温度最终能降至约26 ℃;在60 ℃高温极限工况下,3 h内4测点平均温度最终能降至约31 ℃,防护服护臂内外侧平均温度最终均能降至约32 ℃,低于人体的灼痛临界温度45 ℃。因此该防护服有良好的降温效果,能满足夏季户外工作者的热舒适性要求。     

An experimental technique to evaluate the effective thermal conductivity of Y2O3 stabilized ZrO2 coatings

An experimental device was set up to determine thermal resistance and conductivity of 8% yttria-stabilized zirconia deposited by plasma spray method on cylindrical specimen. In this experimental setup, coated surface of the sample was exposed to a high temperature environment and inner metal surface was cooled by flowing air, simulating actual gas turbine applications. Overall heat resistance at the outside surface of thermal barrier coating was adopted to assess thermal advantage due to the thermal barrier coating deposited on air-cooled cylindrical specimen. 28% less heat was extracted at 1000°C by applying 1.2 mm thick thermal barrier coating. Temperatures of the outside surface of the coated samples increased with increasing coating thickness with respect to the same furnace temperature since the sample with thicker coating was less thermally conductive and retarded heat transfer. The overall heat resistances of samples between the outside surface of sample and the flowing air inside the sample assembly were estimated. Then, the thermal conductivity of coating could be determined from the difference of overall thermal resistances of two selected samples with varying coating thickness.     

Comparison of Oxidation and Thermal Shock Performance of Thermal Barrier Coatings

Operating temperatures in gas turbine engines have reached to 1200°C with the latest developments in coating technology. Thermal shock and furnace oxidation tests are widely used to determine thermal barrier coating (TBC) performance and its durability in aircraft applications. This paper presents the results of thermal shock and furnace oxidation tests, carried out with regard to the microstructure and TGO (thermally grown oxide) growth behavior of TBC systems. Isothermal oxidation behavior of TBCs was evaluated through examination of microstructure, formation, and growth behavior of TGO layers at 1200°C for different time periods in furnace oxidation tests. On the other hand, thermal shock behavior of TBC was evaluated through examination of its durability at 1200°C with thermal shock test, which was carried out until the coating failure became visible. The relationship between the TGO growth and oxidation behavior was discussed using furnace oxidation test results.     

Synthesis of bioactive β-TCP coatings with tailored physico-chemical properties on zirconia bioceramics

The objective of this work was to develop a synthesis procedure for the deposition of β-TCP coatings with tailored physico-chemical properties on zirconia bioceramics. The synthesis procedure involved two steps: (i) a rapid wet-chemical deposition of a biomimetic CaP coating and (ii) a subsequent post-deposition processing of the biomimetic CaP coating, which included a heat treatment between 800 and 1200 °C, followed by a short sonication in a water bath. By regulating the heating temperature the topography of the β-TCP coatings could be controlled. The average surface roughness (R_a) ranged from 42 nm for the coating that was heated at 900 °C (TCP-900) to 630 nm for the TCP-1200 coating. Moreover, the heating temperature also affected the dissolution rate of the coatings in a physiological solution, their protein-adsorption capacity and their bioactivity in a simulated body fluid.     

Thermal and crystallization behavior of zirconia precursor used in the solution precursor plasma spray process

Yttria stabilized zirconia (7YSZ) solution precursor has been successfully used in the deposition of high durability thermal barrier coatings. In this paper, the thermal and crystallization behaviors of 7YSZ precursor were investigated by TG-DTA, FTIR and XRD. The results show that the precursor decomposition and crystallization temperatures greatly depend on heating rate e. g. 74°C for the crystallization temperature when tripping the heating rate. With a 10 °C/min heating rate, the weight loss due to precursor pyrolysis occurs predominantly at temperatures below 500 °C. A small weight loss due to the oxidation of residual carbon is detected from 800 °C to 950 °C. The complete crystallization of the tetragonal phase was determined to be around 500 °C by DTA and XRD analyses with a 10 °C/min heating rate. The crystallization kinetics and the activation energy of amorphous 7YSZ precursor were investigated by variable heating rate DTA. The calculated activation energy is 66.2 kJ/mol. The Avrami parameter value was determined to be 2.68, which indicates that crystallization nucleation and growth is diffusion-controlled. The crystalline phase of 7YSZ coatings deposited by the Solution Precursor Plasma Spray process was identified by XRD and Raman spectrum. The average YSZ grain size in the SPPS coating was determined to be 61 nm.     

Effect of laser glazing on the thermo-mechanical properties of plasma-sprayed LaTi2Al9O19 thermal barrier coatings

Conventional duplex (DL) and functionally graded (FG) LaTi₂Al₉O₁₉ (LTA) coatings were deposited over C263 nickel alloy by air plasma spray (APS) and compared with subsequent laser glazing processes. The effect of laser glazing on adhesion strength and thermal barrier performance was investigated. The thermal barrier effect was measured using the temperature difference technique involving infrared (IR) rapid heater and the adhesion strength was measured using the scratch tester. The surface morphology and microstructure were analyzed by optical microscopy (OM), Scanning Electron Microscope (SEM) and 3D profilometer. Based on the experimental results, the laser glazing showed a remarkable temperature drop after IR rapid heating. The changes in porosity and grain refinement make more contributions to the temperature drop of the laser-glazed coatings than that of as-sprayed coatings. The temperature drop is about 110°C for laser-glazed LTA FG coating after 100?s of IR flash, while the drop in DL as-sprayed coating is 60°C compared to the base material.