Virtual internal thermal work evaluation in the multifield variational statements for the analysis of multilayered structures

The principle of virtual displacements(PVDs)extended to elasto-thermo-electric problems includes virtual internal elastic,thermal and electric works.The governing equations have displacement vector,temperature and electric potential as primary variables of the problem,and the elasto-thermal,elasto-electric and pure elastic problems are obtained as particular cases by deleting the appropriate contributions in the general elasto-thermo-electric variational statement.The most sensitive issue is given by thermal coupling because the thermo-elastic and thermo-electric effects change depending on the type of load and analysis considered(mechanical load,temperature or electric potential imposed and free vibration analysis).This feature means that the form of the virtual internal thermal work in such variational statements changes depending on the analysis performed and the load applied.Results about multilayered plates and shells suggest the appropriate extension of the variational statement for each analysis,and they give an exhaustive explanation for several forms of the PVD proposed.

Influence of Different Surface Treatments of H13 Hot Work Die Steel on Its Thermal Fatigue Behaviors

Thermal fatigue checking is the general failure of hot work die steels, which is relative with the structures and properties of the steels and the stress alternated during the employment. The Uddeholm test method on thermal fatigue is used to compare the behaviors of different samples, which are treated with plasma nitriding、plasma sulfur carbon nitriding、boronizing or not treated. The results show that the nitriding improves the thermal fatigue property of the tool steel, while the plasma sulfur carbon nitriding and the boronizing impair the property. The mechanisms are induced as follows. By increasing the hardness and changing the stress distribution in the surface layer, surface treatment can decrease the plastic deformation and the tensile stress during the cycling. Therefore, the generation and growth of the cracks are restrained. On the other hand, as results of surface treating, in the surface layer the toughness declines and the expanding coefficient ascendes; the latter change caused the strengthening of the tensile and compressive stress during the cycling. Thus the resistance to thermal fatigue is weakened. Whether or not the surface treatment is favor to thermal fatigue of tool steels relies on which factor is dominant.

Thermal stability of cold worked microstructure of MP159 alloy

In order to know the longest permissible thermal exposure time during which the cold worked (CW) microstructure would remain unchanged, the effect of the thermal exposure at temperatures ranging from 910?℃ to 1?070?℃ on the microstructure was investigated for MP159 alloy by optical microscopy and transmission electron microscopy (TEM). Such a study can provide guidance for determining reasonable hot forging parameters of fasteners. The results indicate that the intersecting network of fine platelets in CW microstructure are thermal stable when thermal exposure temperature does not exceed 920?℃. When thermal exposure temperature exceed 920?℃, the intersecting network of fine platelets will dissolve, but the thermal exposure temperature has the longest permissible thermal exposure time during which the intersecting network of fine platelets will not dissolve.

Thermal Behaviors of Work Roll in Finishing Trains of Hot Rolling

In order to analyze the thermal field and thermal contour of work roll in finishing trains of hot rolling in rolling process, a quasi two-dimension implicit finite difference model is developed. To improve the calculating speed and precision, some special solutions are introduced, including the development of this model, the simplification of boundary conditions and the computation of heat transfer coefficients. The results show that these solutions of thermal behaviors of work roll are very much efficient and the model can be used as an on-line profile and fatness control model of large industrial mills.

Preparation and Property of Chromium Carbide Thermal Diffusion Coating on Cold Working Die Materials

Thermal diffusion （TD） salt bath chromizing of cold working dies was studied. Firstly, it obtained an ideal salt bath formula by comparing with a variety of formulas, and then obtained the influence rule of coating thickness based on studying of some process parameters. The microstructure morphologies and phase structures of the TD chromizing coating were investigated by X-ray diffraction （XRD）, energy-dispersive spectrometry （EDS） and other modern analysis methods. Meanwhile, it carried out a system of testing and analysis of coating, such as hardness, wear resistance, etc.

Variable Thermal Comfort Index for Indoor Work Space in Office Buildings: A Study in Germany

International standards state the thermal comfort requirements that office spaces must comply with. These are based on a model developed by Prof. Paul Ole Fanger of the Centre for Indoor Environment and Energy, Denmark. Today, forty-year research shows an evolution in these experiences. The work presented here is to develop a tool to evaluate the thermal comfort of working environments of office buildings. A methodology is devised on the basis of on-site measurements and questionnaire responses. For measurements, a mobile unit equipped with sensors is used, whereas the questionnaire obtains user responses on thermal quality of the work space. The thermal conditions of thirty office buildings presenting different acclimatization systems have been surveyed. The correlation between objective and subjective data allows developing a formula that shows the thermal comfort level for a given environment as a function of local aspects. For the surveyed buildings, the resulting comfortable temperature was 23.3℃, and the minimum percentage of user individuals experiencing discomfort with such temperature was 7%.

Role of entropy generation minimization in thermal optimization

Thermal optimization is very important for improving the performances of thermal systems. In engineering, the entropy generation minimization （EGM） has been widely used to optimize and evaluate the performances of thermal systems. However, the consistency between the EGM and the optimization objective should be specified when the EGM is used. In this paper, we discuss the view angle of irreversibility of entropy generation, and show that entropy generation directly reflects the exergy destruction or the ability loss of doing work. As the design objective in a thermal system is not often consistent with the view angle of irreversibility of entropy generation, the EGM may not lead to the optimal value of the design objective. In heat transfer and heat-work conversion, the inconsistence between the design objectives and the EGM is shown with some examples, and the applicability of the EGM is found to be conditional. The “entropy generation paradox” in heat exchanger analyses is also discussed, and it is shown that there is no direct monotonic relation between the minimum entropy generation rate and the best heat transfer performance of heat exchangers.

Effects of Y_2O_3 on Thermal Shock of Al_2O_3/TiCN Composites

Thermal shock resistance of Al2O3-TiCN(30%)-Y2O3(0.2%) composite was studied by hot pressing(HP) method at different temperatures. The study shows that thermal shock resistance of the material is determined by its microstructure and reinforced mechanism. According to SEM and calculation of thermal shock, the fractured surface of Al2O3-30%TiCN-0.2%Y2O3 composite is undulate. The residual strength of Al2O3-30%TiCN-0.2%Y2O3 is higher than Al2O3-30%TiCN at 200～800 ℃ after thermal shock. Cracks initiation resistance (R′)and cracks propagation resistance (R″″)of Al2O3-30%TiCN-0.2%Y2O3 composite increases 12% and 5% respectively compared with that of Al2O3-30%TiCN. It matches with experimental results. The addition of Y2O3 forms YAG that inhibits crystal growth, and increases fracture stress, fracture toughness, cracks initiation resistance and cracks propagation resistance. Therefore, thermal shock resistance increases. The fracture work of Al2O3-30%TiCN and Al2O3-30%TiCN-0.2%Y2O3 composites are 132 and 148 J·m-2 respectively.

Wear and Thermal Stress Analysis of Side Dam for Twin Roll Strip Casting

The simulation of the work roll temperature field was carried out by means of ANSYS software, and the thermal crown of the roll along its axis was obtained. The thermal-structural coupled element and contact element were introduced. In the simulation of work roll temperature field, the convert boundary condition and the transient thermal contact between the roll and strip were studied. Besides, the dynamic variation of the work roll temperature and the transient temperature distribution of the work roll during hot rolling were investigated. The calculated results were in good agreement with the measured data.

Effect of Rare Earth Composite Modification on Microstructure and Properties of a New Cast Hot-Work Die Steel

The effects of RE modification on structure and the properties of a new cast hot work die (CHD) steel were investigated. The grains of the CHD steel are refined by RE modification. With the increase of RE addition, both grain size and inclusion amount are reduced. Appropriate amount of RE results in decrease in inclusion amount and formation of spheroidal inclusions uniformly-distributed in steel, so that the morphology and distribution of inclusions are improved. RE composite modification favors the formation of bainite, austenite and fine lath martensite with dense dislocation. When the residual RE content reaches 0.02%, no obvious changes in strength and hardness are found, while fracture toughness and threshold of fatigue crack growth are increased. The impact toughness, elongation and reduction of cross sectional area are increased by a factor of two, and thermal fatigue resistance is also improved.

Experimental Studies on Thermal Performance of a Pulsating Heat Pipe with Methanol/DI Water

The effect of working fluid on the start-up and thermal performance in terms of thermal resistance and heat transfer coefficient of a pulsating heat pipe have been studied in the present paper. Methanol and de-ionized water has been selected as the working fluid. The minimum startup power for DI water was obtained at 50% filling ratio and for methanol at 40%. The optimum filling ratio in terms of minimum startup power and minimum thermal resistance was 50% for DI water and 40% for methanol. The minimum thermal resistances for DI water and methanol were observed at vertical orientation. The evaporator side heat transfer coefficient for water was slightly more, while the condenser side heat transfer coefficient was appreciably more than that of methanol. Studies were also conducted for start-up time and temperature at different orientations and it was found that the PHP charged with methanol worked efficiently at all orientations.

Development and application of a new hot-work die steel for hot stamping

A new hot-work die steel for hot stamping was developed, and used the die for mass production. The produced die showed good performance owing to its high heat conductivity and wear-resistant characteristics. Two different benchmarking hot-work die steels were investigated, and then compared in terms of their impact ductility, temper characteristics ,heat conductivity, and thermal stability. The result of the high-temperature friction wear test indicated that oxidative wear was the main mode in high temperature. On the basis of the comparison and test results, the alloying composition of the new hot-work die steel was especially designed. The new die steel showed good performance with good wear-resistant quality, as well as temper hardness and heat conductivity of HRC 50 and 34.3 W/（ m ~ K）, respectively. Furthermore, without surface plasma nitriding, the die made of the new steel had no obvious galling with 6 142 strokes. After surface plasma nitriding, the die completed 40 000 strokes with good surface. The die life is expected to exceed 200 000 strokes.

Study on Microstructures and Properties of Several Kinds of Hot Working Die Steel

This paper deals with the microstructures and properties of AISI H13(4Cr5MoSiV1), UHB QRO 90M and 4Cr3Mo2V steels, and then discusses the means of improving the service life of hot working die. The results show that increase of quenching temperature improves the resistance to thermal fatigue and tempering stability. Fine heat treatment process can produce fine dispersed carbides. Shot peening and cryogenic treatments can raise the compressive stresses at surface as well as the resistance of tempering greatly. Under the condition that a compound layer is not engendered, ionnitriding process can restrain the initiation and propagation of fatigue crack and enhance the resistance to thermal fatigue. Vapor surface treatment provides the ways to protect and lubricate the die by the porous films of Fe 3O 4, which are formed on the die surface. Electrical spark surface strengthening process forms compounds with high melting point and high stability on the die surface and thus enhances the properties of die's resistance to oxidation efficaciously. Besides, QRO 90M and 4Cr3Mo2V steels, because of the superiority in designing of composition, have better tempering stability and softening resistance than 4Cr5MoSiV1 steel.

APPLICATION OF RARE EARTH IN SURFACE HEAT TREATMENT OF HOT-WORKING DIE STEELS

This paper studies a compound treatment. i. e. liquid S , N,C co-diffusing with rare earth (RE) and then oxidization , for hot-working die steels , and the effect of RE on thermal fatigue behavior of the diffused layer. XRD and SEM energy spectrum prove that trace RE element actually penetrates into the surface layer of steels. The result shows that RE can reduce the gradient of change of hardness in diffused layer, improve the morphology and distribution of compounds , and reduce the degree of surface alligator crack for thermal fatigue. The behavior of thermal fatigue of hot-working die steels is raised by 70% or so after the application of RE. The effect of RE is analysed according to the theory.

5A发射电流空心阴极热特性模拟分析

采用有限元分析方法,建立了国产5 A空心阴极的热仿真模型,并进行了模型校验和典型工况下的温度场分析。结果显示:模型能够较好地反映空心阴极内部的能量传动过程,温度的仿真结果与试验比对误差小于5%;加热电流是造成空心阴极温度差异的主要原因;环境温度主要影响着空心阴极的外部部件温度,并且在太阳辐照影响时的高温环境更有利于推力器的启动;空心阴极加热且处于自持放电状态时,发射体温度在环境温度0℃和94℃下分别达到2 122℃和2 126℃,已接近发射体材料的耐温极限,因此空心阴极必须避免此极端使用工况。

18CrNiMo7-6齿轮钢的热压缩变形行为及显微组织演变

采用热模拟方法研究了18CrNiMo7-6齿轮钢在变形温度900~1150℃、应变速率0.01~5 s-1条件下的热压缩变形行为;建立了基于Arrhenius模型的全应变本构方程,采用该方程对流变应力曲线进行预测;根据动态材料模型绘制热加工图,并结合热加工图系统地研究显微组织演变特征。结果表明:试验钢的峰值应力随应变速率的增加或变形温度的降低而增大,动态回复和动态再结晶是热变形过程中的主要软化机制;采用建立的全应变本构方程预测得到流变应力曲线与试验结果基本吻合,预测真应力与试验结果的相对误差小于4.715%,说明该模型可以精确地模拟18CrNiMo7-6齿轮钢的热压缩变形行为。试验钢的适合热加工工艺参数为变形温度1050~1150℃、应变速率0.1~1 s^(-1),此时组织为均匀细小的再结晶晶粒,晶粒尺寸在5~15μm。随着变形温度的升高或应变速率的降低,原始奥氏体晶粒不断被动态再结晶晶粒取代,且动态再结晶程度和再结晶晶粒尺寸增大。

Numerical study of n-heptane/benzene separation by thermal diffusion column

In this article,numerical simulations are performed to investigate the performance of the thermal diffusion column for the separation of n-heptane/benzene mixture.The present work tried to optimize column by analyzing significant parameters such as feed flow rate,temperature and cut.In order to obtain the hydrodynamic and temperature and mass distribution inside thermal diffusion column,computational fluid dynamic(CFD) method is applied to solve the Navier-Stocks equations.Numerical simulations are conducted to study the main parameters in both stationary and time-dependent conditions.By using the separation work unit as a function of cut,the optimal cut for maximum SWU occurs within a limited range of 0.47-0.5 for feed rate between 0.5 and 4 g min^-1.Our findings reveal that the optimum feed rate in the range of optimum cut is about 1 g min^-1.In transient study,results show that the best cut for reaching to steady-state condition is θ=0.5.

液态金属在电子热控中的应用进展与挑战

液态金属作为当下科学和工业前沿的璀璨明珠,不仅是实际应用中不可或缺的重要组成部分,更是一个充满未知奇迹的探索领域。其独特的物理性质使得它在电子热控方面备受瞩目。文中剖析了热控应用中至关重要的典型液态金属的物理参数和性能,深入挖掘了液态金属在电子热控中的应用场景,介绍了它作为热界面材料、相变储能材料和循环工质的现状和研究进展,并进一步阐述了液态金属在电子热控应用中面临的主要技术挑战,提出了应对这些技术挑战的技术途径,指出了液态金属未来的研究方向。

Zr-2.5Nb合金高温流变行为及热加工图研究

在应变速率0.01~10 s^(-1),变形温度750~880℃(中高(α+β)相区)的条件下,对Zr-2.5Nb合金进行了热变形行为研究,以掌握高温流变行为及热加工稳定性,为Zr-2.5Nb合金锻造和挤压提供依据。

一体集成小型化YIG调谐带阻滤波器组件热仿真分析

通过Ansys Workbench对一体集成小型化YIG调谐带阻滤波器组件进行热仿真分析,得出在自然散热条件下,组件中部分发热元件的温度为170℃以上,超过了元件允许工作温度125℃,组件可靠性无法得到保证。为此,在组件底部增加散热板以增大散热面积,改善散热条件。仿真结果表明,各发热部件的温度大幅下降,组件中发热元件的最高温度是PTC热敏电阻,为118℃,线圈、控制驱动、大功率三极管温度分别为99℃、104℃、116℃,均低于元件允许工作温度,满足设计要求,保证组件全温度环境下可靠工作。在一体集成小型化组件的设计中,合适的元器件布局和散热方式是组件的可靠性的重要设计因素,且利用热仿真分析,可以降低组件的实物试制成本和验证成本,缩短研发周期,提高研发效率。