A parametric study of the heat absorption capacity of metallic moulds-fundamental patterns of its time variation

The capacity of a metallic mould to absorb heat from the solidifying casting plays a key role in controlling the metallurgical, technological and mechanical properties of the casting. Therefore, the main objective of the present paper is to reveal the nature of the mould cooling capacity-time history and to establish a map for the fundamental patterns of this relationship. The extent of the mutual interactions among the principal variables is also examined. The analysis of the present work is confined to a spherical mould of uniform wall thickness to simulate a unidirectional heat flow. The solution of the problem is obtained through finite element approximation. An approximate analytical solution, based on the heat balance integral method, is developed to extend the fundamental solution obtained in this study to the case of transient boundary condition. Application of this analytical development is demonstrated using experimental data. Analysis of the results indicated that the time variation of the mould cooling capacity follows one of two distinctive patterns depending on the combination of govering variables. An unexpected behaviour has been observed; the negative effect of Biot modulus under conditions of no preheat. The effects of various governing variables on the mould cooling capacity have been discussed and summarised.     

FE numerical simulation of mould temperature field during the continuous casting of steel

In this paper, the three-dimensional transient model of the mould temperature is established and the temperature variation is analyzed when the thickness of the mould wall and the cooling rates are different. For the numerical computation, a corresponding finite element method (FEM) program is developed with FORTRAN language, and six-face and eight-node isoparameter elements are applied; the Newton method is used to solve the heat equations. The experimental data have been used to validate the model. It is shown that the appropriate mould wall thickness is 10 mm and the different parts of the mould should correspond with cooling water of different rates.     

Effect of thermal radiation on convection heat transfer in cooling channel of photovoltaic thermal system

The effect of thermal radiation on convection heat transfer in flat-box type cooling channel of photovoltaic thermal system with tilt angle of 30 degree was studied by 3D numerical simulation under constant heat flux boundary condition. The temperature contours and velocity fields of fluid near the outlet were obtained. The variations of wall temperature and convection Nusselt number along flow direction for all the separate walls composing the cooling channel were compared and analyzed. The results show that due to thermal radiation, the deflection of the maximum velocity region to heated top wall, together with the asymmetry of temperature field is weakened. For natural convection, radiation promotes the formation of multi-vortices. For mixed convection, heat transfer on all the cooling channel walls is enhanced under the condition of lower heat flux while heat transfer on heated top wall is deteriorated when the heat flux is relative high. Also, pressure re-rising is promoted by thermal radiation.     

盘式制动器热-结构耦合的数值建模与分析

在充分考虑移动热源且速度可变效应影响、盘与片摩擦界面间热流耦合的基础上,根据制动盘与摩擦片的实际几何尺哌寸,建立一个紧急制动工况下三维瞬态热-结构耦合的计算模型,运用大型有限元软件ANSYS中的非线性有限元多物理场方法,数值模拟盘式制动器的制动过程.揭示制动过程中制动盘瞬态温度场/应力场的分布规律,发现二者之间存在着耦合关系,二者随制动时间明显地呈现周期性变化,这些周期波动是由移动热源产生的热流冲击和对流换热影响的交替作用所引起的,且其变化周期随制动时间的延长而增大.并初步探讨制动盘产生径向裂纹的原因.     

A new parameter for assessment of the cooling rate of metallic moulds—Concept and practical implications

The cooling (or heating) rate of the metallic mould is of fundamental importance as it controls the rate of extraction of the latent heat of solidification, and consequently the morphology and the properties of the casting. Its evaluation is, however, difficult because it is both position-and time-dependent. In this study, a new parameter has been developed to assess the cooling (or heating) rate of the mould as an entity. This physically meaningful parameter, which is based on Kondratyev's regular regime theory, is characterised by its universality (as it can be calculated or measured for moulds of various geometric forms) and its constancy (as it is both position- and time-independent over a period of the transient process). In the present paper, Kondratyev's theory is extended to the case in which the change in the enthalphy of the body and the combined convective and radiative heat losses are not necessarily equal in magnitude. An approximate closed-form solution for the relationship between this “mould cooling rate constant” and the process variables is developed for a spherical mould of a uniform wall thickness, using the heat balance integral method. Available experimental data were used to confirm the validity of the concept of the mould cooling rate constant and to demonstrate its practical implications.     

聚合物反应成型模具加热系统热源强度反演与试验研究

反应成型模具加热系统热源强度的求解是一个典型的热传导反问题,即在给定的温度场解的条件下,求解热管的加载工况。根据反应成型模具加热系统的传热特性,结合线性热传导叠加原理,推导出模具加热系统热传导多源项反演算法,针对反演问题的不适定性,通过选择平方范数来提高反演稳定性和精度。设计单型腔反应固化成型模具,开发温度控制系统,搭建温度场测试试验平台。试验结果证明基于线性热传导叠加原理的多源项反演算法,在解决工程问题上是有效的、可靠的。     

螺旋锥齿轮磨齿温度场研究与应用分析

根据螺旋锥齿轮的数控磨削原理,采用热传导和矩形移动热源理论及有限元分析方法,建立了磨齿温度场有限元分析3D模型和磨齿瞬态温度场。对热和结构两个物理场进行耦合,仿真分析了磨齿瞬态热应力和热变形。实例和试验分析表明:磨齿瞬态最高温度远高于磨齿稳态温度,且位于磨削弧中心;其他各点的瞬态温度,随位置、时间以及其他影响因素的不同,呈现不同的变化规律。磨齿瞬态热应力、热变形与磨齿瞬态温度密切相关,同时还受结构、材料特性和磨削条件等因素的影响,磨齿瞬态最大热应力与热变形位于磨齿瞬态最高温度附近。在其他条件相同时,采用油基磨削液的瞬态最高温度、热应力与热变形均比采用水基磨削液时要大。     

基于温度场的磨齿热特性研究

根据七轴五联动螺旋锥齿轮磨齿机的结构模型和数控磨削原理,采用热传导和矩形移动热源理论及有限元分析方法,建立了磨齿温度场有限元分析3D模型和磨齿瞬态温度场。由此,对热和结构两个物理场进行耦合,仿真分析了磨齿瞬态热特性。实例分析表明,磨齿瞬态最高温度远高于磨齿稳态温度,且位于磨削弧中心;其它各点的瞬态温度,随位置、时间以及其它影响因素的不同,呈现不同的变化规律。磨齿瞬态热应力、热变形与磨齿瞬态温度密切相关,同时还受结构、材料特性和磨削条件等因素影响,磨齿瞬态最大热应力与热变形位于磨齿瞬态最高温度附近。在其它条件相同时,采用油基磨削液的瞬态最高温度、热应力与热变形均比采用水基磨削液时要大。这些研究为控制螺旋锥齿轮磨削质量以及磨齿热变形的修形提供了依据。     

承压热冲击瞬态下反应堆压力容器下降环腔内三维热工水力分析

以压水堆核电厂承压热冲击分析评定技术研究(PTS确定性分析方法研究项目)为背景,针对核电厂PTS瞬态下RPV下降环腔内热工水力分析问题,基于通用计算流体动力学软件Fluent,采用合适的对流换热分析和湍流模型,建立了RPV下降环腔内的三维热工流场分析模型,模拟分析RPV下降环腔内的三维流动与换热情况。重点模拟得到了RPV下降环腔内的三维流场分布和RPV内壁面的温度分布,并且在某些瞬态时刻得到了典型的热工水力现象即羽流(Plume)现象。得到的RPV下降环腔内详细的热工流场数据和羽流现象,为PTS下RPV应力分析和完整性提供了热工数据。     

基于格子Boltzmann方法的动压气体轴承黏性热耗散研究

箔片气体轴承微间隙内的流场常处于滑移区,甚至过渡区,会出现一些微观效应,其热特性的研究采用宏观方法已不再合适。为研究不同工况下动压气体轴承间隙热特性变化规律,基于格子Boltzmann方法建立包含黏性热耗散项的径向轴承间隙传热数值模型;采用总能形式的双分布函数热模型,通过有限差分离散将其应用到贴体网格中,同时引入速度滑移和温度阶跃边界条件,通过数值计算得到不同参数下的轴承间隙气膜温度分布,并分析了不同埃克特数（Ec）、偏心率和转速条件以及温度阶跃对黏性热耗散的影响。结果表明,当Ec数、偏心率和转速增大时,气膜最高温度增加,两侧的温度阶跃增加;温度阶跃效应的忽略均会导致黏性热耗散量不同程度的低估。     

Thermal displacement error compensation in temperature domain

Thermal displacement errors are becoming more and more important in the precision engineering field where the specifications are ever increasing. This paper proposes a novel technique to compensate in-plane thermal displacement errors in a thin plate under a moving disturbance heat load. The displacement error is evaluated at the point of the moving heat load. The technique utilizes Thermal Modal Analysis (TMA) as a means to analyze the transient temperature distribution in the plate and estimate the thermal displacement field resulting from that temperature field. The temperature field is controlled by applying additional heat loads to the plate to control and eliminate some of the modes in the temperature domain which have the largest influence to the thermal displacement error. The theory of thermal modal analysis and the developed technique of controlling modes in the temperature domain are explained. The experimental setup and results are shown to validate the control of the thermal modes.     

金属铸造界面传热系数的试验研究及其确定

金属铸造凝固过程中,在接触界面间会产生热阻.热阻的大小随空间和时间变化,常常主导着热传导的过程,通常将热阻的影响表示为界面传热系数,在温度场数值模拟中,铸件与铸型间的界面传热系数是关键的参数.利用有限元分析软件ANSYS结合试验数据,模拟了铸造凝固过程的温度场,分别考虑了不同界面传热系数对模拟结果的影响,并将模拟数据与试验结果进行了比较,发现了金属型铸造界面传热系数随时间变化的规律,以及铸件与铸型的接触位置对界面传热系数的影响.     

小型铣削中心主轴-轴承系统的热态特性分析

对主轴建模,计算出与主轴实际工作条件相适应的热边界条件:轴承发热量和传热系数,确定主轴的约束条件,用COSMOS有限元分析软件对小型铣削中心主轴-轴承系统的热态特性进行分析,得到主轴稳态温度场分布、瞬态温升和主轴热变形情况,为主轴的进一步优化设计提供理论依据.     

无纬带绑扎机带式制动器摩擦热效应分析

根据无纬带绑扎机带式制动器的摩擦力学与热力学模型,进行了制动器稳态与瞬态热效应分析,确定了摩擦热与摩擦功率之间的关系.探讨了摩擦热量在摩擦副材料中的分配状况,研究并得到了摩擦副平衡温度和摩擦副可长期连续工作的条件.建立了基于ANSYS的制动器热效应分析模型,得到不同时间摩擦副温度场分布状况和温度随时间变化的状况.     

制动鼓的热-结构耦合分析

以有限单元法与结构力学、热分析理论为基础,利用ANSYS对制动鼓在几种典型制动工况下进行瞬态热分析,根据制动鼓的受力情况和热分析结果对紧急制动工况下进行静态热-结构间接耦合分析。较准确地反映了制动过程中制动鼓的温度场和制动结束时应力分布情况,为制动鼓的材料选择、尺寸设计提供了一定的理论依据。     

橡胶注射机模具加热系统温度场数值模拟与实验研究

橡胶注射机模具温度场的均匀性直接影响橡胶硫化,而模具温度场的均匀性主要取决于热板的加热效果.由于没有科学依据,热板中热管的功率以及热电偶位置都是凭借经验进行选择,导致模具加热不均匀和温控精度低,直接影响橡胶注射机的使用性能,也是目前橡胶注射机企业碰到的最大难题.采用有限元法,对加热系统进行瞬态温度场模拟仿真,得到了合理的热管排布方式与热电偶位置,并通过实验,验证了分析结果切实可行.     

Thermoelectrically controlled micronozzle — A novel application for thermoelements

This paper introduces and assesses the concept of the recently invented thermoelectrically controlled micronozzle (TECMN). A generalized quasi-one-dimensional model for gas flow, which is influenced by area variation and by wall heat transfer, is considered. In order to assess the merits of wall temperature control in micronozzles, the flow in the micronozzle is solved numerically for cases of convergent wall heating, divergent wall cooling, and a combination of both. Thermal efficiency and specific impulse are affected by heat exchange through the side wall of the micronozzle. By cooling the divergent section, kinetic energy increases, thus improving thermal efficiency. The mass flow rate is decreased in all cases that include convergent section heating, thereby enhancing specific impulse. The combination of convergent section heating with divergent part cooling results in significant performance enhancement in terms of thermal efficiency and specific impulse. To determine the TECMN wall temperature profile, we developed a one-dimensional general energy model for a thermoelement (TE) subject to an electric field as well as for heat convection on the lateral surface. The energy equation is analytically solved for constant properties and for Joule heating equivalent to heat convection. The temperature profile is then imposed on the quasi-one-dimensional flow model, which is solved numerically for various mass flow rates and exit wall temperature (cold junction). As the exit section wall temperature and mass flow rate decrease, the utilization of TEs to control the temperature of micronozzle walls considerably increases the Mach number at exit.     

可降解秸秆花盆压制模具瞬态热分析

针对某型号花盆实验压制模具加热需要较长时间,模芯周围温度分布不均匀等问题,本文运用三维建模软件UG对模具进行实体建模,并运用ANSYS对花盆模具加热过程进行瞬态热分析,得出模具加热到正常工作温度所需时间和正常工作时花盆模具的温度分布云图,为缩短花盆模具的加热时间及模具电热管分布等问题提供了参考依据。     

小型精密CVD金刚石热沉片的制备研究

CVD金刚石具有优异的导热性能,在微电子热沉应用方面有着广阔的应用前景。利用ICP工艺制造了硅模具,利用有限元对CVD系统中硅模具的温度场和流场进行了研究,在硅模具内制备了小型精密CVD金刚石热沉片。试验结果表明模具法能够获得表面品质好、形状和尺寸精度很高的小型金刚石热沉片。     

城市轨道交通车辆踏面制动热应力仿真分析

分析了城轨列车在踏面制动方式下车轮踏面热疲劳裂纹产生的机理,并建立了车轮制动过程瞬态温度场三维有限元模型,采用整体输入热流和对流换热的简化模式为基础的传统理论的热应力计算方法,计算车轮在连续两次紧急制动工况下的热温度场及热应力场,为确定城轨列车制动方式及列车制动距离等技术规范提供计算依据。